EMEP/CCC-Report 5/98 - NILU
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Pilot measurements of nitrogen containing species in air
Arne Semb, Alena Bartonova, Jan Schaug, Anke Lükewille and Kjetil Tørseth
|NILU |: |EMEP/CCC-Report 5/98 |
|REFERENCE |: |O-8852 |
|DATE |: |AUGUST 1998 |
| | | |
EMEP Co-operative Programme for Monitoring and Evaluation of the Long-range Transmission of Air Pollutants
in Europe
Pilot measurements of nitrogen containing species in air
Arne Semb, Alena Bartonova, Jan Schaug, Anke Lükewille and Kjetil Tørseth
Contents
Page
1. Introduction 5
2. Measurements and data collection 7
2.1 Measurement programme 7
2.2 Measurement sites 7
2.3 Sampling and chemical analysis 7
2.4 Data collection 9
3. Results and discussion 11
3.1 Average concentrations 11
3.2 Daily variations in measured concentrations during the four periods 15
3.3 Dissociation equilibria for ammonium nitrate 26
3.4 Temperature and humidity during the four measurement periods 32
3.5 Comparison between measurements with denuders and impregnated filters 33
4. Summary and conclusions 39
5. References 40
Appendix 1 Data statistics and summaries 43
Appendix 2 Denuder and filter summaries 49
Pilot measurements of nitrogen containing species in air
1 Introduction
At ambient temperatures and concentration levels, gaseous nitric acid and hydrochloric acid may form ammonium nitrate and ammonium chloride by reaction with ammonia gas. These ammonia salts are in a state of chemical equilibrium with their gaseous precursors, increasing temperatures cause the salts to dissociate, while decreasing temperature and increasing relative humidity increases the concentrations of the ammonia salts relative to concentrations of their gaseous precursors (Tang, 1980; Stelson and Seinfeld, 1982(a,b); Pio and Harrison, 1987).
While ammonia is mainly emitted from animal husbandry and agricultural activities (e.g. Asman, 1992; ECETOC, 1994), nitric acid is the atmospheric oxidation product of nitrogen oxides emitted from motor vehicles and combustion processes, much in the same way as sulphur dioxide is oxidized to sulphuric acid. Both sulphuric acid and nitric acid will combine with ammonia to form the respective ammonium salts, but formation of ammonium sulphate and nitric acid is thermodynamically more favourable than the formation of ammonium nitrate and sulphuric acid.
These reactions are of considerable importance for the atmospheric transport and deposition of both oxidized and reduced nitrogen. Reported dry deposition velocities for gaseous nitric acid (Dollard et al., 1987; Meixner et al., 1987) are very high , while ammonium nitrate in the form of submicron particles have much lower deposition rates. The deposition velocity for ammonia is also higher than the deposition velocities for ammonium sulphate and ammonium nitrate.
Field measurements (e.g. Ferm, 1986; Allen et al., 1989) have generally confirmed the chemical dissociation equilibria for ammonium nitrate and ammonium chloride, and their dependence on temperature and relative humidity. However, since concentrations and conditions may vary considerably during the sampling period, measured average concentration products tend to exceed the equilibrium dissociation products. Also, ammonium nitrate is not the only nitrate-containing aerosol component, since nitric acid may react also with alkaline aerosol particles and with sea-salt aerosols (Hillamo et al., 1992; Geernaert et al., 1996).
Ambient concentrations and climatic conditions vary widely across Europe, and this also influences the proportions of gaseous HNO3 and NH3 in relation to the particle-bound nitrate and ammonium concentrations. Ferm (1986) has found that the gaseous nitric acid concentrations correspond typically to only 10-25% of the concentrations of particulate nitrate at the Swedish west coast. The low partial pressures of ammonia and nitric acid suggest that nitrates were often present as sodium nitrate rather than as ammonium nitrate. Similar conclusion were arrived at by Hillamo et al. (1992) from cascade impactor samples collected in Southern Norway. Low concentrations of nitrates were generally associated with sodium and chloride in the size range 2-8 µm, but higher concentrations of nitrate occurred also in association with ammonium in the submicron particle size range. Ottley and Harrison (1992) also found that, over the North Sea, concentrations of ammonia and nitric acid were too low to sustain the existence of NH4NO3, and that the dissociation of NH4NO3 and the further oxidation of NO2 led to the formation of nitrate on the surface of marine aerosol droplets.
Mehlmann and Warneck (1995) also found nitrate associated with sea-salt sodium in “clean air” samples at Deuselbach. However, in continental areas, ammonium nitrate is the major nitrate-containing aerosol salt. The products of the measured concentrations of ammonia and nitric acid are therefore generally consistent with the dissociation equilibrium values for ammonium nitrate, higher values are mostly explainable in terms of variable conditions and concentrations during the sampling period (Allen et al., 1989).
It is generally accepted that the concentrations of gaseous nitric acid and ammonia can only be appropriately measured using diffusion denuders (Ferm, 1979, 1982, 1986; Allegrini et al., 1987). Filter-pack sampling, where ammonium nitrate is collected on an aerosol filter previous to the absorption of nitric acid and ammonia on successive impregnated filters will generally result in overestimation of the nitric acid and ammonia component because of volatilization of ammonium nitrate from the aerosol filter during the sampling period and during storage prior to analysis. Because of this effect, filter-pack sampling is only reliable for the sum of gaseous and particulate nitric acid and ammonia. In some cases, however, acceptable results may be obtained (Harrison and Kitto, 1990; Pio, 1992).
Within the EMEP measurement programme, the requirements are that nitrate and nitric acid and ammonium and ammonia are to be measured, preferably by denuder sampling. Alternatively, filter-pack sampling, which only allow quantification of the sums of the gaseous and particulate components, may also be used. Very few denuder sampling results have been reported to the CCC.
Knowledge of the partitioning of these species between the gaseous and the particle-bound phases is essential for comparison with model estimates and estimation of deposition velocities. Because of the importance of this issue, and in order to improve the measurement methods, the 1992 EMEP Workshop on Measurements of Nitrogen-Containing Compounds, at Les Diablerets in Switzerland, recommended that a pilot programme of measurements should be carried out at 12 stations during 4 periods of minimum 2 weeks, in December 1992, and March, June and September 1993. The recommendation from the workshop was endorsed by the Steering Body of EMEP in September 1992.
This report focus on the measurements of nitric acid, ammonia, and nitrates and ammonium in airborne particles with denuders and filter packs. Components like nitrogen dioxide and PAN were also made available from a few sites and these results can be found in the data listing at the end of the report.
2 Measurements and data collection
1 Measurement programme
The pilot measurements consisted of separate measurements by denuder technique of nitric acid (HNO3) and nitrate (NO3-) in aerosols, and ammonia (NH3) and ammonium (NH4-) in aerosols. Additionally, total nitrate and total ammonium in aerosols measured by impregnated filter methods, nitrogen dioxide and PAN concentrations when available, ammonium and nitrate in precipitation, records of temperature and relative humidity, were to be forwarded to the CCC.
The measurements should be carried out during 4 periods of minimum 2 weeks, in December 1992, and March, June and September 1993.
2 Measurement sites
Ten sites took part in the pilot measurements as follows:
DK33 Lille Valby
DE7 Neuglobsow
CH2 Payerne
FI9 Uto
IT4 Ispra
HU2 K-Puszta
NO1 Birkenes
RU14 Pushkinskie Gory
SE2 Rorvik
SE12 Aspvreten
The Danish site, Lille Valby, is not a regular EMEP site. It is located in horizontally homogeneous agricultural fields, 6 km NNE of Roskilde (40,000 inhabitants), and 35 km W of Copenhagen (850,000 inhabitants), one to two km W of the site is the Roskilde Fiord. In NS direction, a highway with approx. 6,000 cars/day runs along the coast. The geographical co-ordinates are 5541'N, 1207'E and the elevation is 15 m above sea level.
3 Sampling and chemical analysis
Four sites specified in detail the sampling and analysis methods they have used.
Payerne (CH2)
Two denuder monitoring units with airflow about 2 l/min. were used. The coating solution for HNO3 was 0.2% NaCl in methanol, for NH3 1.5% oxalic acid in methanol. Filters (cellulose nitrate filters Sartorius, 25 mm diameter, 1.4 µm pore size) were coated for HNO3 by 1% NaCl solution in water and for NH3 by 1% oxalic acid in water. Exposed filters were extracted in 8 ml pure water and the sample was frozen prior to analysis.
HNO3 is measured as NO3- by ion chromatography, and ammonia as NH4+ by the indophenol method.
Neuglobsow (DE7)
NO2 was measured by Saltzman method with spectrophotometric analysis.
HNO3/NO3- was measured by NaOH impregnated filters with ion chromatography.
NH3/NH4+ was measured by oxalic acid impregnated filters, with flow injection analysis. NO3- in precipitation was measured by daily bulk collectors with ion chromatography.
NH4+ in precipitation was measured by daily bulk collectors, with flow injection analysis.
Lille Valby (DK33)
Single denuder measurements were performed.
The NH3 denuders were coated with 1.5% oxalic acid solution in ethanol. The NH4+ filters were also coated by 1.5% oxalic acid in ethanol. The flow was 3 l/min. for December 92, March 93 and April 93 sampling, and was reduced to 2 l/min. in June 93. The filters were analysed by the indophenol method. Detection limits were 0.01 µg/m3 for NH3 and 0.11 µg/m3 for NH4+.
The HNO3 denuders were coated with 1.5% solution of NaCl in ethanol. The NO3- filters were coated with 1.5% solution of NaF in deionized water. The flow was 1 l/min. The species were analysed by ion chromatography with UV detection (216 nm). Detection limits were 0.09 µg/m3 for HNO3 and 0.45 µg/m3 for NO3-.
Filter pack measurements with teflon filters were used for comparison measurements of NH3- (HNO3), NH4+ and NO3-. The packs consisted of a Teflon Gelman TF-1000 filter (pore diameter 1 µm), two filters impregnated with sodium carbonate (1.5% solution in ethanol/water), and a filter impregnated with 1.5% oxalic acid. The flow was 40 l/min. NH3 and NH4+ were analysed by the indophenol method, other ions by ion chromatography. Detection limits were 0.04 µg/m3 for NH3, 0.02 µg/m3 for NH4+, 0.002 µg/m3 for HNO3 and 0.01 µg/m3 for NO3-.
Uto (FI9)
Sampling of HNO3 and NO3 was by denuder technique, analysis by ion chromatography with detection limit for gaseous and particulate components 0.031 µg N/m3. Gaseous NH3 and particulate NH4+ was analysed by ion chromatography, with detection limits for gaseous and particulate components 0.006 µg N/m3.
Total NH4 was sampled by one-staged filtration method for gases and aerosols (NH3 + NH4+), analysis was done by spectrophotometric indophenol method with detection limit 0.01 µg N/m3. Total NO3+ was sampled by two-staged filtration method for gases and aerosols (HNO3 + NO3-), samples were analysed by ion chromatography with detection limit 0.01 µg N/m3.
The precipitation samples were taken into summer bulk collector NILU RS1. Sampling time was 24 hours. The ions were analysed by ion chromatography, with detection limit for NO3- 0.01 mg N/l and for NH4+ 0.002 mg N/l.
NO2 was sampled by NaI impregnated sinter method, as 12 hours samples. Analysis method was spectrophotometric, with detection limit 0.03 µg N/m3.
Pushkinskie Gory (RU14)
Nitrogen dioxide was measured using two methods:
1. NO2 samples were collected on glass sorption tubes, filled with glass beads, wetted by a non-drying solution of potassium iodide and sodium arsenate. Nitrogen dioxide was determined with the Griss technique.
2. Same sampler as Aspvreten, NO2 determined by reaction with NEDA and sulphanilamide.
The results provided by the two methods are in a good agreement: the correlation coefficient is 0.87, linear regression of method 1 on method 2 gives slope 0.94 with std.error 0.13, i.e., not significantly different from zero, intercept -0.02, std.error 0.14, i.e. not significantly different from 0. Since more data were available measured by method 2, these were included in the database, while measurement results from method 1 were dropped.
4 Data collection
The four measurement periods were:
Period I: 30.11-20.12.1992, period II: 12.4-2.5.1993, period III: 1.6-21.6.1993, and period IV: 6.9-25.9.1993. However, several countries have measured also during other periods (see Table 1).
All denuder samples were taken as daily samples, except at RU14, where sampling for the first three periods was done twice a week. In case of the daily samples, occasionally the sampling period of the daily sampling was one to two hours shorter than 24 hrs.
Nitrogen dioxide, temperature and relative humidity when measured more often than daily were converted into daily means corresponding to the hours when the daily sample was taken.
For site DE7, the units of measurement of the nitrogen species did not specify, whether the results are given in µg/m3 or in µg N/m3. For this site, and in all other such cases (often for NO2), it was assumed, that the values were in µg N/m3. Site Lille Valby (DK33) provided all the denuder data in ppt. These were recalculated into µg/m3 using pressure of 1 atmosphere and temperature of 20 C.
Table 1: Overview of the measuring periods.
|Site |Period I |Period II |Period III |Period IV |Other periods |
| |(1992) |(1993) |(1993) |(1993) | |
|DK33 |1.12-20.12 |4.12.-2.5. |1.6.-21.6. | |1.3.-4.12. |
|DE7 |- |12.4.-2.5. |1.6.-21.6. |6.9.-25.9. |- |
|CH2 |- |4.12.-2.5. |17.5.-21.6. |- |29.12.-19.12.93 |
|FI 9 |- |13.4.-5.2. |- |1.9. - 29.9. |- |
|IT4 |1.12-20.12. |- |7.6 - 26.6. |30.8. - 18.9. |11.3. - 30.3. |
|HU1 * |30.11-20.12. |4.12.- 2.5. |1.6. - 21.6. |6.9. - 25.9. |* |
|NO1 |30.11-20.12. |12.4. - 2.5. |1.6. - 21.6. |6.9. - 26.9. |15.2. - 7.3. |
|RU14 |24.12-10.1.93 |12.4. - 30.4. |1.6. - 19.6. |6.9. - 25.9. |- |
|SE2 |30.11-21.12. |11.4.- 3.5. |31.5. - 21.6. |1.9. - 30.9. |- |
|SE12 |- |4.12. - 2.5. |31.5. - 21.6. |7.9. - 24.9. |15.2. - 7.3. |
*HU1: Denuder measurements are a standard measurement method. Only the intensive measuring periods are included in this report.
Overview of which compounds or meteorological data are available for individual sites and measuring periods are given in Table 2.
Table 2: Overview of data availability for the measuring periods.
|Species |CH2 |DE7 |DK33 |FI9 |HU1 |IT4 |NO1 |RU14 |SE2 |SE12 |
|HNO3D |II, III* | |I, II, |II, IV |I-IV |I-IV |I-IV* |I-IV |I-IV |II-IV* |
| | | |III* | | | | | | | |
|NO3D |II, III* | |I, II, |II, IV |I-IV |I-IV |I-IV* |I-IV |I-IV |II-IV* |
| | | |III* | | | | | | | |
|NH3D |II, III* | |I, II, |II, IV |I-IV |I-IV |I-IV* |I-IV |I-IV |II-IV* |
| | | |III* | | | | | | | |
|NH4D |II, III* | |I, II, |II, IV |I-IV |I-IV |I-IV* |I-IV |I-IV |II-IV* |
| | | |III* | | | | | | | |
|HNO3/NO3 | |II, III, IV| | | | | | | | |
|NH3/NH4 | |II, III, IV| | | | | | | | |
|NO3F |II, III* | |a |II, IV | | | | |I-IV | |
|NO4F |II, III* | |a |II, IV | | | | |I-IV | |
|NO3P |II, III* |II, III, IV| |II, IV | |I-IV | | |I-IV | |
|NO4P |II, III* |II, III, IV| |II, IV | |I-IV | | |I-IV | |
|NO2 |II, III* |II, III, IV| |II, IV | |I-IV | |I-IV | |II-IV* |
|PAN |II, III* | | | | |I-IV | | | | |
|RH | | | |II |I-IV |I-IV | |I-III |I-IV |II-IV* |
|TEMP | | | |II |I-IV |I-IV | |I-III |I-IV |II-IV* |
D: Denuder sampling
F: Independent filter pack
P: Precipitation
HNO3/NO3 resp. NH3/NH4: Total amount obtained from denuder sampling, when no individual values are available.
RH: Relative humidity
Temp: Temperature
Measuring periods: I, II, III, IV - see Table 1, *.. other periods, see Table 1.
a Evaluation of agreement between denuder and filter pack is provided.
3 Results and discussion
1 Average concentrations
The average concentrations of ammonia and nitric acid, and the corresponding particle-bound ammonium and nitrate are presented for the various periods in Table 3,and together with other simple statistics in Appendix 1.
As indicated in the table, sampling periods at the individual sites do not always coincide. Not all participants were able to start their measurements in December 1992, and several countries have added a fifth sampling period. The main objective of the measurements were separate measurements of nitric acid and nitrate in aerosol particles, and ammonia gas and ammonium in particles, respectively. In addition, measurements of nitrogen dioxide and PAN were reported from some of the sites. Because of the importance of non-seasalt sulphate in the formation of ammonium aerosol salts, the concurrent concentrations of this component in the aerosol is also listed. These data are taken from the routinely reported EMEP measurement data, when available.
Table 3 shows that there are considerable differences in the concentration levels from site to site, and also on a seasonal basis. Concentrations are generally higher at the continental sites, including the Danish site (DK33). Also, the concentrations at all sites tended to be higher in the spring period, although the concentrations at the most northerly sites were clearly more influenced by meteorological conditions.
The concentrations of ammonium ion was also always slightly less than the amount required to form the ammonium salts of sulphate and nitrate, confirming that ammonium is the most important cation in the atmospheric aerosol, but also that sulphate and particularly nitrate must also be present as other salts, in association with sea-salt components or alkaline particles.
Relatively high concentrations of ammonia gas were found at IT4, CH2, DK33 and at RU14, while low concentrations were found at SE12, and at FI9.
The concentrations of nitric acid gas were low at all sites, and much lower than the concentrations of particulate nitrate, except at the Hungarian site (HU2, K-puzsta)
Table 3: Average concentrations at the sites during the measurement campaigns.
Unit: (g/m3, as N or S, respectively.
|SE12, Aspvreten: |HNO3-N |NO3--N |NH3-N |NH4+-N |SO4---S |
|930215-939215 |0.10 |0.09 |0.04 |0.67 |1.24 |
|930413-930502 |0.09 |0.13 |0.07 |0.81 |0.99 |
|930601-930621 |0.06 |0.06 |0.06 |0.28 |0.49 |
|930907-930924 |0.05 |0.15 |0.02 |0.40 |0.41 |
|NO1, Birkenes: | | | | | |
|921130-921220 |0.03 |0.23 |0.11 |0.32 |0.55 |
|930215-930307 |0.04 |0.18 |0.16 |0.25 |0.29 |
|930412-930502 |0.14 |0.60 |0.21 |1.26 |1.32 |
|930601-930621 |0.07 |0.20 |0.32 |0.39 |0.49 |
|930906-930926 |0.03 |0.25 |0.26 |0.43 |0.46 |
|IT4, Ispra | | | | | |
|921201-921220 |0.11 |1.37 |2.68 |2.22 |1.65 |
|920311-930330 |0.55 |1.89 |2.14 |3.23 |2.01 |
|920607-930626 |0.45 |0.58 |3.52 |2.07 |1.72 |
|930830-930918 |0.28 |0.42 |3.53 |1.55 |1.37 |
|HU2, K-puzsta | | | | | |
|921130-921220 |0.49 |0.72 |0.86 |2.15 |n.a. |
|930412-930502 |0.48 |0.26 |1.34 |1.00 |1.27 |
|930601-930621 |0.45 |0.23 |1.40 |1.22 |1.30 |
|930906-930925 |0.32 |0.32 |0.88 |1.04 |0.84 |
|DK33, Lille Valby: | | | | | |
|921201-921220 |0.16 |1.05 |n.a. |n.a. |n.a. |
|930301-930325 |0.13 |3.23 |0.93 |5.35 |n.a. |
|930412-930502 |0.25 |1.40 |1.49 |3.45 |n.a. |
|930601-930620 |0.20 |0.85 |1.39 |3.35 |n.a. |
|CH2, Payerne: | | | | | |
|930407-930502 |0.15 |0.86 |1.93 |1.86 |1.15 |
|939608-930621 |0.16 |0.25 |2.15 |1.02 |1.19 |
|931129-931219 |0.04 |1.08 |2.03 |1.76 |0.98 |
|RU14; Pushkinskie Gory: | | | | |
|921130-921221 |0.03 |0.17 |0.09 |0.48 |1.08 |
|930411-930503 |0.10 |0.09 |1.20 |0.69 |0.97 |
|930531-930621 |0.04 |0.03 |1.46 |0.13 |0.69 |
|930906-930927 |n.a. |0.09 |n.a. |2.06 |n.a. |
|SE2, Rörvik | | | | | |
|921130-921221 |0.12 |0.59 |0.13 |0.95 |0.58 |
|930411-930503 |0.14 |0.78 |0.45 |1.09 |1.55 |
|930531-930621 |0.16 |0.30 |0.16 |0.70 |0.90 |
|930906-930927 |0.08 |0.27 |0.13 |0.76 |0.78 |
|FI9, Utö | | | | | |
|930413-930502 |0.20 |0.41 |0.03 |0.53 |0.97 |
|930901-930930 |0.02 |0.03 |0.04 |0.19 |0.53 |
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Figure 1: November–December. Low concentrations of gaseous HNO3 at all sites except HU2. Ammonia concentrations are low at RU14, NO1 and SE2. DK33 does not have NH3 or NH4+ data for this period. Relatively high ammonia concentrations at HU2 and IT4.
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Figure 2: February–March. Three sites have reported data for this period, which is not within the original time schedule. SE12 and NO1 report low concentrations of NH3 and HNO3. High concentrations of ammonium nitrate and high ammonia concentrations occurred at DK33.
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Figure 3: April–May. Ammonia concentrations were low at FI9, SE12, and NO2, moderate at SE2, and high at DK33, CH2, HU2 and IT4. High concentrations of ammonia also occurred at RU14. HNO3 concentrations were also generally low, but increase with decreasing latitude. SE12 and RU14 reported low NO3- concentrations, but nitrate concentrations at the other sites are generally higher than in November–December.
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Figure 4: June. Low HNO3 concentrations, but increasing with decreasing latitude. Generally low NO3- concentrations, except at DK33. High concentrations of ammonia at RU12, DK33, CH2, HU2 and IT4.
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Figure 5: Generally low concentrations, particularly with respect to nitric acid, nitrate and ammonia. CH2 had relatively high nitrate and high ammonia concentrations, while HU2 had moderate and IT4 had high ammonia concentrations. Both these sites had low to moderate nitrate concentrations.
2 Daily variations in measured concentrations during the four periods
Results from the individual measurements are presented in Figures 6-15, which show the measured average concentrations of gaseous nitric acid, particulate nitrate, gaseous ammonia, and particulate ammonium, on a daily basis. The concentrations of sulphate aerosol are also given when available. Statistics and summaries of the results from the four measurement periods are given in Appendix 1.
The measured concentrations of gaseous nitric acid were generally much lower than the concentrations of particulate nitrate. At the sites IT4, CH2 and DK33, relatively high concentrations of gaseous ammonia are effective in converting nitric acid to ammonium nitrate and suppressing ammonium nitrate dissociation. The relative amount of gaseous nitric acid to nitrate in particles increase during the summer months at these sites. Relatively high concentrations of gaseous ammonia are also measured at HU2, but here the measured concentrations of nitric acid are comparable to the concentration of nitrate particles.
Concentrations of ammonia are low, but still measurable at SE2 and NO1. However, the concentrations of gaseous nitric acid relative to the concentrations of particulate nitrate at these sites were on average only 21 and 16%.
At SE12 and FI9, concentrations of ammonia were very low. Nitric acid and nitrate concentrations were also low, however. This is also the case for RU14.
Particulate ammonium is usually associated with particulate sulphate as ammonium sulphate. Ammonium nitrate and gaseous ammonia can only occur when sulphate particles are fully neutralized (as (NH4)2SO4). Comparison of the concentrations of particulate sulphate, particulate ammonium and particulate nitrate can therefore be used to test if the particulate nitrate is in the form of ammonium nitrate or as other salts.
It is seen that there is generally good correlation between particulate ammonium and particulate sulphate. At IT4 the measurements indicate that ammonium nitrate is an important ammonium compound, but the excess of ammonium over the amount corresponding to ammonium sulphate is often too low to explain the particulate nitrate concentrations. As there is also an excess of ammonia, chemical absorption of nitric acid onto alkaline aerosol particles is the most likely explanation. The same conclusion may to some extent apply to the results from CH2. At HU2 the ammonium concentrations relative to the sulphate concentrations are lower than corresponding to ammonium sulphate. This appears also to be the case at DE7. Sulphate concentration data are not available from the Danish station Lille Valby, but it would appear likely that ammonium nitrate is a major component, together with ammonium sulphate.
At SE2 and NO1, the highest nitrate concentrations seem to be ammonium nitrate, but low and moderate concentrations of nitrate appear to be associated with other cations. This is in accordance with previous observations, which show that nitrate is often associated with sea-salt particles.
The low concentrations at SE12 and FI9 makes it difficult to draw firm conclusions, but it appears that ammonia/ammonium concentrations levels are insufficient in relation to the formation of ammonium sulphate, and that any nitrates present may be connected with other cations than ammonium. The relative high fraction of gaseous nitric acid at FI9 supports this observation. Ammonia concentrations at RU14 are higher than at the sites adjacent to the Bothnian Sea, but both nitrate and nitric acid concentrations are very low compared to the sulphate concentrations.
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Figure 6: Measurement results from Lille Valby (DK33).
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Figure 7: Measurement results from Rörvik (SE 2).
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Figure 8: Measurement results from Aspvreten (SE 12).
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Figure 9: Measurement results from Birkenes (NO1).
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Figure 10: Measurement results from Utö (FI 9).
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Figure 11: Measurement results from Pushkinskie Gory (RU 14).
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Figure 12: Measurement results from Neuglobsow (DE 7).
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Figure 13: Measurement results from K-puszta (HU 2).
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Figure 14: Measurement results from Payerne (CH 2).
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Figure 15: Measurement results from Ispra (IT4).
3 Dissociation equilibria for ammonium nitrate
Bassett and Seinfeld (1983) formulated an atmospheric equilibrium model of sulphate and nitrate aerosols and made calculations for different scenarios for NH3, HNO3 and H2SO4 concentrations The results show that when there is an ammonia deficiency, the ammonia will react with sulphuric acid and only traces of nitrate will be present in airborne particles as pH decreases. The formation of ammonium nitrate is thus determined by the amounts of components available, as well as by the thermodynamic stability of the compound under different conditions of temperature and relative humidity.
In Figures 16-19 the products of the measured NH3 and HNO3 concentrations have been plotted against the inverse absolute temperature. The temperatures were taken from the measured average temperatures during the sampling period. Conversion of the concentrations in µg/m3 to partial pressures in ppb were made assuming that volume concentrations refer to 20 (C and 1 atm.
When ammonium nitrate is present in particles, they will coexist together with nitric acid and ammonia gases in air at equilibrium. Expressions for predicting the dissociation constant for ammonium nitrate as a function of temperature and humidity have been derived from thermodynamics by Stelson and Seinfeld (1982a). The Figures 16-19 present calculations of the dissociation constant (Kp) as a function of inverse temperature at different relative humidities. At high relative humidity the ammonium nitrate particles will be in a liquid state. The relations between Kp and inverse temperature are presented at 99, 95 and 75 per cent relative humidities for liquid particles, and the correspond relation (upper line) for solid particles is also given.
These diagrams are useful in relating the measured concentrations of ammonia and nitric acid to the expected concentrations, assuming thermodynamic equilibrium with solid or deliquescent ammonium nitrate.
At ambient concentrations and equilibrium, points should not be seen above the (upper) line for solid particles in the Figures. When the measurements are daily averages, however, temperature and humidity may vary appreciably during day and night. Most of the measured concentration product are well below the estimated equilibrium value for solid ammonium nitrate, and in the high range of expected relative humidities, this is more pronounced in the Nordic countries in Figures 16 and 17 than in the central and southern parts of the Continent in Figure 18. Also, many of the samples do not represent a situation with ammonium nitrate present, since nitrate often occur as sodium nitrate. At HU2 and CH2 (Figure 18), the concentration products are generally within the expected range for the higher temperatures, but are sometimes appreciably higher at the low temperature and low concentration end of the diagram which may be explained by changing conditions during the sampling period. In agricultural areas, ambient ammonia concentrations are typically 5-10 ppb, or 200-400 nmol/m3. This is not sufficient to suppress the dissociation of ammonium nitrate in the daytime under summer conditions, but ammonium nitrate will usually form during the night when the temperature drops and the relative humidity increases. In addition, ambient ammonia concentrations at ground level are also generally higher within the inversion layer during the night than at daytime. Significant concentrations of both ammonia and nitric acid cannot be present at the same time, but sampling over an extended time period with denuders may detect both species when the composition of the air changes during the sampling period. Figure 19 illustrates the diurnal variation of the concentrations showing hourly calculations of the Kp during 24 hours at Birkenes three days (open symbols) assuming equilibrium between ammonia, nitric acid and ammonium nitrate particles. The corresponding 24 hour measured averages are given as solid symbols. When day and night temperatures are very different, as they are 10 June, the diurnal variation in the ambient concentrations can be several factors of ten. This also corresponds well with observations made by Parrish et al. (1993). They documented that the NOy levels and its partitioning were strongly influenced by the diurnal evolution of the nocturnal and convective boundary layers at flatland sites.
[pic]
Figure 16: Product of measured concentrations of ammonia and nitric acid as a function of inverse daily average temperature. Solid lines represent calculations of Kp for NH3 and HNO3 with liquid particles at 75, 95, and 99% relative humidity, and with solid particles. Utö (FI9, *) and Aspvreten (SE12, 0).
[pic]
Figure 17: Product of measured concentrations of ammonia and nitric acid as a function of inverse daily average temperature. Solid lines represent calculations of Kp for NH3 and HNO3 with liquid particles at 75, 95, and 99% relative humidity, and with solid particles. Lille Valby (DK33, +), Birkenes (NO1, ), and Rörvik (SE2, ().
[pic]
Figure 18: Product of measured concentrations of ammonia and nitric acid as a function of inverse daily average temperature. Solid lines represent calculations of Kp for NH3 and HNO3 with liquid particles at 75, 95, and 99% relative humidity, and with solid particles. Payerne (CH2, (), K-puszta (HU2, *), and Ispra (IT4, ).
[pic]
Figure 19: Diurnal variation of Kp for NH3 and HNO3 concentrations at Birkenes three days (open symbols). The corresponding 24 hour measured averages are given as solid symbols.
4 Temperature and humidity during the four measurement periods
Table 4 presents air temperature and relative humidity during the individual measurement campaigns at the sites, where these measurements are available. Site RU14 has performed measurements twice a week during the first three intensive measuring periods, and the values are three to four day averages.
Table 4: Overview of atmospheric conditions.
| | | |Relative humidity (%) | | | |Relative humidity (%) | | |
|Sampling |Site |No. of |Mean value |Min. |Max. |No. of | |Min. |Max. |
|period | |samples | | | |samples | | | |
|1st period |HU2 |20 |89.95 |75.0 |99.0 |20 |2.66 |-2.0 |7.6 |
| |IT4 |20 |84.85 |30.0 |93.0 |20 |3.03 |-.5 |9.0 |
| |RU14 |2 |78.50 |65.0 |92.0 |2 |-4.25 |-6.0 |-2.5 |
| |SE2 |22 |91.11 |71.5 |99.4 |22 |3.21 |-5.8 |6.6 |
| | | | | | | | | | |
|2nd period |FI9 |20 |76.51 |57.5 |90.3 |20 |4.44 |.8 |9.1 |
| |HU2 | 19 |63.68 |49.0 |93.0 |19 |13.41 |6.6 |17.4 |
| |SE2 |21 |66.71 |47.7 |91.9 |21 | 8.70 |1.4 |17.3 |
| |SE12 |18 |72.66 |58.0 |85.1 |18 | 6.24 |-.6 |12.9 |
| | | | | | | | | | |
|3rd period |HU2 | 21 |52.33 |34.0 |72.0 |21 |20.90 |16.4 |24.6 |
| |IT4 |20 |71.40 |54.0 |90.0 |20 |18.99 |15.6 |22.0 |
| |RU14 | 6 |76.33 |62.0 |88.0 |6 |11.52 |8.4 |14.5 |
| |SE2 |22 |73.88 |57.5 |86.1 |22 |12.45 |8.9 |19.5 |
| |SE12 |18 |75.27 |57.1 |92.2 |19 |11.69 |7.2 |17.2 |
| | | | | | | | | | |
|4th period |HU2 |18 |70.50 |62.0 |87.0 |18 |16.24 |12.8 |22.7 |
| |IT4 |20 |76.75 |54.0 |98.0 |20 |15.77 |13.5 |17.7 |
| |SE2 |21 |81.42 |62.8 |92.8 |21 | 8.76 |4.9 |12.3 |
| |SE12 |18 |82.51 |62.2 |93.7 |18 | 8.13 |4.4 |12.4 |
| | | | | | | | | | |
|5th period | | | | | | | | | |
| | | | | | | | | | |
|6th period |CH2 |21 |77.88 |6.3 |93.7 |21 | 4.09 |-3.2 |9.2 |
| | | | | | | | | | |
|7th period |IT4 |20 |62.80 |21.0 |95.0 |20 | 7.40 |3.0 |12.8 |
| |SE2 |1 |34.45 |34.5 |34.5 |1 |2.58 |2.6 |2.6 |
During the first intensive period (December 1992), average daily temperature was between -4.3 and +3.2 C, with daily minimum at RU14 of -6.0 C and daily maximum at IT4 of 9.0 C. Daily average of relative humidity ranged between 78% and 91%, with lowest daily average at IT4 (30%) and highest at SE2 (99%).
During the second intensive period (April 1993), daily average temperature ranged between 4.4 and 13.4 C, with lowest daily average of -0.6 C at SE12, and highest of 17.4 at HU2. Relative humidity ranged between 52 and 73%, with highest daily average at HU2 (34%) and highest daily average at SE12 (92%).
During the third intensive period (June 1993), average temperature ranged between 8.1 and 16.2 C, with lowest daily average of 4.4 observed at SE12 and highest daily average of 22.7 observed at HU2. Average relative humidity for the period ranged between 52 and 76%, with lowest observed daily average at HU2 (34%) and highest observed daily average at SE12 (92%).
During the fourth intensive period (September 1993), average temperatures were between 8.1 and 16.2 C, with lowest measured 4.4 at SE12 and highest 22.7 at HU2. Relative humidity in the period was between 70 and 83%, with lowest and highest daily average at IT4 (54% and 98%).
Outside the intensive measurement periods, less data are available. Periods 5 and 7 cover mid-February to mid-April, period 6 December 1993.
Figure 20 shows the relation between temperature and relative humidity at deliquescence for ammonium nitrate particles. In the lower triangle of the Figure the particles will be solid, and liquid in the upper part. The relation between temperature and relative humidity is given by Stelson and Seinfeld (1982b). The presence of sea salts in the particles seems to give a liquid phase at lower relative humidity than indicated.
[pic]
Figure 20: Deliquescence for pure ammonium nitrate particles.
5 Comparison between measurements with denuders and impregnated filters
Denuder measurements and filter pack measurements of both HNO3/NO3- and NH3/NH4+ were made available from CH2, FI9, NO1 and SE2, and of NH3/NH4+ alone from DK33. Appendix 2 gives summaries of the denuder and filter measurements. Figures 21-29 give the scatter plots of the results from the various sites.
Results of linear regression calculations between respectively total NO3- and NH4+ from denuders and filters are presented in Table 5 with the regression coefficients and their standard error. The calculations were based on all available data:
Denuder concentration = intercept + slope * filter concentration.
The spread in the data tend to be larger for the HNO3/NO3- results than for the reduced nitrogen components, which can be seen both from the standard deviation of the slope and from the correlation coefficient. The agreement between denuder and filter measurements for both HNO3/NO3- and NH3/NH4+ is generally good, with slopes mostly not significantly different from one and intercepts not different from zero.
Table 5: Comparison between denuder and filter results.
|Site |Compound |Intercept |Slope |No. of cases |Correlation |
| | | | | |coefficient |
|CH2 |NH3/NH4 |0.07 (0.20) |0.924 (0.050) |33 |0.96 |
|CH2 |HNO3/NO3 |-0.06 (0.09) |0.933 (0.099) |33 |0.86 |
|DK33 |NH3/NH4 |-0.30 (0.13) |0.978 (0.021) |58 |0.98 |
|FI9 |NH3/NH4 |-0.02 (0.03) |1.161 (0.048) |50 |0.96 |
|FI9 |HNO3/NO3 |-0.09 (0.04) |1.094 (0.084) |47 |0.89 |
|NO1 |NH3/NH4 |0.14 (0.03) |1.039 (0.029) |102 |0.96 |
|NO1 |HNO3/NO3 |0.04 (0.02) |1.292 (0.049) |102 |0.93 |
|SE2 |NH3/NH4 |0.36 (0.12) |0.593 (0.069) |87 |0.68 |
|SE2 |HNO3/NO3 |0.07 (.06) |0.917 (0.070) |86 |0.82 |
There are some exceptions from this in Table 5; the slope for NH3/NH4+ at FI9 is slightly too high, and the slopes for the HNO3/NO3 measurements at NO1 and for the NH3/NH4 measurements at SE2 are respectively too high and too low. The intercepts for NH3/NH4 at NO1 and SE2 are also both slightly too high. The slightly higher denuder results for NH3/NH4+ from FI9 are clearly seen in
Figure 26.
The apparent low denuder results at SE2 compared with the filter results in
Table 5 is not significant, as seen from the large spread in the data in Figure 28.
Figure 29 compares the NO1 denuder sum of HNO3 and NO3 results with the corresponding filter results. The spread in the data is very low, but the slope is clearly higher than 1, as also calculated from the regression. Since the nitrate size distribution (in contrast to the sulphate distribution) is bimodal and thought to contains a fraction larger than 1 containing sodium nitrate and other nitrates from reactions with sea salt and soil particles, this could explanation larger denuder concentrations. In this case the correspondence between the two methods would be different from one site to another, as it is here, pending upon the availability of
[pic]
Figure 21: Comparison of filterpack and denuder measurements of the sums of ammonium and ammonia concentrations at Payerne (CH2).
[pic]
Figure 22: Comparison of filterpack and denuder measurements of the sums of nitrate and nitric acid concentrations at Payerne (CH2).
[pic]
Figure 23: Comparison of filterpack and denuder measurements of the sums of ammonium and ammonia concentrations at Lille Valby (DK33).
[pic]
Figure 24: Comparison of filterpack and denuder measurements of the sums of ammonium and ammonia concentrations at Utö (FI9).
[pic]
Figure 25: Comparison of filterpack and denuder measurements of the sums of nitrate and nitric acid concentrations at Utö (FI9).
[pic]
Figure 26: Comparison of filterpack and denuder measurements of the sums of ammonium and ammonia concentrations at Birkenes (NO1).
[pic]
Figure 27: Comparison of filterpack and denuder measurements of the sums of nitrate and nitric acid concentrations at Birkenes (NO1).
[pic]
Figure 28: Comparison of filterpack and denuder measurements of the sums of ammonium and ammonia concentrations at Rörvik (SE2).
[pic]
Figure 29: Comparison of filterpack and denuder measurements of the sums of nitrate and nitric acid concentrations at Rörvik (SE2).
salts and soil particles. This may at least to some extent be investigated by inspecting the concentrations in the different parts of the denuder system, but would require shorter sampling times than the one presently used due to the diurnal variation in the concentrations.
A few of the single results from the denuders were clearly wrong, and it is evident that accurate denuder measurements require good training and experience. Of this reason one may suspect that some of the inconsistencies between filters and denuders could be due to measurement errors.
4 Summary and conclusions
When inspecting averages over the individual measurement periods it is seen that the sum of the NO3- + SO42- concentrations always was less than the NH4+ concentrations during the periods when all three species were determined. This is due to the presence of other cations e.g. sodium, magnesium, and calcium from soil and sea-spray as well as small contributions from hydroniumions and other cations. The results also show sulphate on average almost without exceptions have larger concentrations than nitrate and that sulphuric acid still gives larger contribution to the acidification than nitric acid. Particulate ammonium is usually associated with particulate sulphate as ammonium sulphate. Ammonium nitrate and gaseous ammonia can only occur when sulphate particles are fully neutralized (as (NH4)2SO4).
On average, the gas concentrations of ammonia and nitric acid are generally lower than the concentrations of ammonium and nitrate in particles. During spring and summer periods, however, the ammonia concentrations are so high at some sites that they exceed the concentrations of sulphuric and nitric acids.
When comparing the nitric acid, ammonia, and ammonium nitrate measured concentrations with thermodynamic calculations of the dissociation constant, the measurement apparently are too high. This is due to highly different concentrations of ammonia and nitric acid during night and day, and that high concentrations of ammonia often occur when the nitric acid concentrations are low (night), and vice versa. The results here indicate that this is more pronounced on the Continent than in the Nordic countries. Calculations of the diurnal variation of Kp show that the variation in ambient concentrations of ammonia and nitric acid can be several factors of ten.
Comparisons of the denuder method for separate measurement of nitric acid, nitrates, ammonia, and ammonium with the impregnated filter method for the sum of nitric acid and nitrates , and ammonia and ammonium, show mostly a good 1:1 correspondence. Some of the sites have more nitric acid/nitrates collected with the denuder than the filter method; this is most pronounced for the measurements at NO1. This may be due to a larger intake velocity in the denuder than in the filter-pack used at this site, causing a more efficient sampling of the larger particle fraction by the denuder. It is known that the nitrate size distribution (in contrast to the sulphate distribution) is bimodal and contains a fraction larger than 1 µm besides the submicron fraction. The larger fraction consists of sodium nitrate and other nitrates from reactions between nitric acid and sea salt and soil particles. A few of the denuder results were clearly wrong and one could also suspect that some of the differences between denuders and filters are due to errors. It is evident that accurate denuder measurements require good training and experience.
One conclusion from the results in this pilot study is that future measurements should focus more on the chemical composition, and include speciation of nitrates other than ammonium nitrate. Size-segregated sampling of aerosols may be used to separate ammonium nitrate from sea-salt and alkaline particles. At some sites shorter sampling periods than 24 hours should be carried out, e.g. separate measurements of gaseous ammonia and nitric acid during day and night, or even shorter sampling time. Continuous measurements would also appear to be useful.
It should also be noted that measured ground-level concentrations of nitric acid and nitrate concentrations are generally much lower than model estimates, while concentrations of nitrate in precipitation are about the same. This apparent inconsistency has yet to be explained.
5 References
Allegrini, I., de Santis, F., di Paolo, V., Febo, A., Perrino, C. and Pazzanzini, M. (1987) Annular denuder method for sampling reactive gases and aerosols in the atmosphere. Sci. Tot. Environ., 67, 1-16.
Allen, A.G., Harrison, R.M. and Erisman, J.-W. (1989) Field measurements of the dissociation of ammonium nitrate and ammonium chloride aerosols. Atmos. Environ., 23, 1591-1599.
Asman, W.A.H. (1992) Ammonia emission in Europe: Updated emission and emission variations. Bilthoven, National Institute of Public Health and Environmental Protection (RIVM Report No. 228471008).
Bassett, M. and Seinfeld, J.H. (1983) Atmospheric Equilibrium Model of Sulfate and Nitrate Aerosols. Atmos. Environ., 17, 2237-2252.
Dollard, G.J., Atkins, D.H.F., Davies, T.J. and Healy, C. (1987) Concentrations and Dry Deposition Velocities of Nitric Acid. Nature, 326, 481-483.
Ferm, M. (1979) Method for determination of atmospheric ammonia. Atmos. Environ., 13, 1385-1393.
Ferm, M. (1982) Method for the determination of gaseous nitric acid and particulate nitrate in the atmosphere. EMEP Expert meeting on chemical matters, Geneva, 10-12 March.
Ferm, M. (1986) A Na2CO3 -coated denuder and filter for determination of gaseous HNO3 and particulate NO3 in the atmosphere. Atmos. Environ., 20, 1193-1201.
Ferm, M. (1986) Concentration measurements and equilibrium studies of ammonium, nitrate and sulphur species in air and precipitation. Dissertation, Department of inorganic chemistry, Göteborg, Sweden.
Geernaert, L.L.S., Vignati, E., de Leeuw, G., Schulz, M., Plate, E. and Højstrup, J. (1996) Influence of sea spray on HNO3 fluxes. J. Aerosol Sci., 27, S97-S98.
Granby, K. (1994) Pers. comm. Ministry of the Environment, Roskilde, Denmark.
Harrison, R.M. and Kitto, A.-M.N. (1990) Field intercomparison of filter pack and denuder sampling methods for reactive gaseous and particulate pollutants. Atmos. Environ., 24A, 2633-2640.
Hillamo, R.E., Pacyna, J.M., Semb, A. and Hanssen, J.E. (1992) Size distributions of inorganic ions in atmospheric aerosol in Norway. Development of analytical techniques for atmospheric pollutants. In: Air Pollution Research Report 41. Brussels, Commission of European Communities, pp 51-65.
Mehlmann, A. and Warneck, P. (1995) Atmospheric gaseous HNO3, particulate nitrate and aerosol size distributions of major ionic species at a rural site in western Germany. Atmos. Environ., 29, 2359-2373.
Meixner, F.X., Franken, H.H., Duijszer, J.H. and van Aalst, R.M. (1987) Dry deposition of HNO3 to a pine forest. In: Proceedings of the 16th International Technical Meeting on Air Pollution Modelling and its Applications. NATO Committee on Challenges of Modern Society, Lindau, Germany.
Ottley, C.J. and Harrison, R.M. (1992) The spatial distribution and particle size of some inorganic nitrogen, sulphur and chlorine species over the North Sea. Atmos. Environ., 26A, 1689-1699.
Parrish, D. D., Buhr, M. P., Trainer, M., Norton, R.B., Shimshock, J.P., Fehsenfeld, F.C., Anlauf, K.G., Bottenheim, J.W., Tang, Y.Z., Wiebe, H.A., Roberts, J.M., Tanner, R.L., Newman, L., Bowersox, V.C., Olszyna, K.J., Bailey, E.M., Rodgers, M.O., Wang, T., Berresheim, H., Roychowdhury, U.K. and Demerjian, K.L. (1993) The total reactive oxidized nitrogen levels and the partitioning between the individual species at six rural sites in Eastern North America. J. Geophys. Res., 98, 2927-2939.
Pio, C.A. and Harrison, R.M. (1987) The equilibrium of ammonium chloride aerosol with gaseous hydrochloric acid and ammonia under tropospheric conditions. Atmos. Environ., 21, 1243-1246.
Stelson, A.W. and Seinfeld, J.H. (1982a) Relative humidity and temperature dependence of the ammonium nitrate dissociation constant. Atmos. Environ., 16, 983-992.
Stelson, A.W. and Seinfeld, J.H. (1982b) Relative humidity and pH dependence of the vapor pressure of ammonium nitrate-nitric acid solutions at 25 (C. Atmos. Environ., 16, 993-1000.
Stelson, A.W. and Seinfeld, J.H. (1982c) Thermodynamic prediction of the water activity, NH4NO3 dissociation constant, density and refractive index for the NH4NO3-(NH4)2SO4-H2O system at 25 (C. Atmos. Environ., 16, 2507-2514.
Tang, I.N. (1980) On the equilibrium partial pressures of nitric acid and ammonia in the atmosphere. Atmos. Environ., 14, 819-828.
Yoshizumi, K. and Hoshi, A. (1985) Size distribution of ammonium nitrate and sodium nitrate in atmospheric aerosols. Env. Sci. Technol., 19, 258-261.
Appendix 1
Data statistics and summaries
Table 1.1: Overview of measurement results, denuder.
|Sampling period |NH3-N |NH4-N |NO3-N |HNO3-N |
| |(µg/m3) |(µg/m3) |(µg/m3) |(µg/m3) |
|1st period | | | | |
|DK33 | | | | |
| No. samples | | | 14 |10 |
| Mean value | | |1.05 |.16 |
| Std.dev. | | |.5 |.1 |
| Minimum | | |.45 |.09 |
| Maximum | | |.2.12 |.26 |
|HU2 | | | | |
| No. samples |20 |9 |9 |9 |
| Mean value | .86 |2.15 |.72 |.49 |
| Std.dev. |7 |1.4 |.5 |.3 |
| Minimum |20 |.08 |.22 |.13 |
| Maximum |54 |4.44 |1.69 |1.13 |
|IT4 | | | | |
| No. samples |20 |20 |20 |20 |
| Mean value |2.68 |2.22 |1.37 |.11 |
| Std.dev. |.6 |1.6 |1.1 |.1 |
| Minimum |.88 |.20 |.09 |.01 |
| Maximum |6.85 |5.26 |3.71 |.54 |
|NO1 | | | | |
| No. samples |21 |21 |21 |21 |
| Mean value |.11 |.32 |.23 |.02 |
| Std.dev. |.1 |.4 |.3 |.0 |
| Minimum | .02 |.05 |.02 | |
| Maximum |.44 |1.46 |1.01 |.10 |
|RU14 | | | | |
| No. samples |4 |5 |6 |6 |
| Mean value | .09 |.48 |.17 |.03 |
| Std.dev. |0 |.3 |.2 |.0 |
| Minimum |.06 |.11 |.04 |.01 |
| Maximum |.12 |.91 |.46 |.05 |
|SE2 | | | | |
| No. samples |22 |22 |22 |22 |
| Mean value |.13 |.95 |.59 |.12 |
| Std.dev. |.2 |1.0 |.6 |.1 |
| Minimum |.02 |.07 |.02 | |
| Maximum |.86 |4.38 |2.19 |.42 |
| | | | | |
|2nd period | | | | |
|CH2 | | | | |
| No. samples |7 |7 |20 |16 |
| Mean value |1.93 |1.86 |.86 |.15 |
| Std.dev. |.7 |2.0 |.5 |.1 |
| Minimum |1.05 |.46 |.15 |.04 |
| Maximum |2.85 |6.16 |1.63 |.28 |
|DK33 | | | | |
| No. samples |21 |21 |17 |16 |
| Mean value |1.49 |3.45 |1.40 |.25 |
| Std.dev. |.7 |2.1 |.8 |.1 |
| Minimum |.33 |.34 |.52 |.12 |
| Maximum |.06 |8.26 |2.84 |.60 |
|FI9 | | | | |
| No. samples |20 |20 |20 |20 |
| Mean value |.03 |.75 |.41 |.20 |
| Std.dev. |.0 |.5 |.2 |.1 |
| Minimum |-.01 |.13 |-.03 |-.03 |
| Maximum |.15 |2.10 |.81 |.58 |
|HU2 | | | | |
| No. samples |19 |9 |9 |9 |
| Mean value |1.34 |1.00 |.26 |.48 |
| Std.dev. |.6 |.5 |.1 |.1 |
| Minimum |.43 |.16 |.14 |.33 |
| Maximum |2.39 |1.62 |.45 |.68 |
Table 1.1 contd.
|Sampling period |NH3-N |NH4-N |NO3-N |HNO3-N |
| |(µg/m3) |(µg/m3) |(µg/m3) |(µg/m3) |
|NO1 | | | | |
| No. samples |20 |20 |20 |20 |
| Mean value | .21 |1.26 |.60 |.14 |
| Std.dev. |.3 |1.0 |.6 |.1 |
| Minimum |.02 |.04 |.11 |.01 |
| Maximum |1.16 |3.01 |2.27 |.37 |
|RU14 | | | | |
| No. samples |6 |6 |6 |6 |
| Mean value |1.20 |.69 |.09 |.10 |
| Std.dev. |.8 |.2 |.0 |.1 |
| Minimum |.32 |.46 |.04 |.04 |
| Maximum |1.97 |1.08 |.14 |.17 |
|SE2 | | | | |
| No. samples |21 |21 |21 |21 |
| Mean value | .44 |1.15 |.80 |.15 |
| Std.dev. |3 |1.1 |.9 |.1 |
| Minimum |.13 |.06 |-.03 | |
| Maximum |.10 |4.27 |2.94 |.62 |
|SE12 | | | | |
| No. samples |17 |16 |17 |18 |
| Mean value | .06 |.81 |.13 |.09 |
| Std.dev. |1 |.6 |.1 |.1 |
| Minimum |.01 |.11 |.02 |.02 |
| Maximum |.28 |1.81 |.42 |.22 |
| | | | | |
|3rd period | | | | |
|CH2 | | | | |
| No. samples |33 |33 |21 |35 |
| Mean value |2.48 |1.16 |.33 |.17 |
| Std.dev. |.3 |.6 |.2 |.1 |
| Minimum |.47 |.17 |.05 |.03 |
| Maximum |5.32 |2.64 |.96 |.34 |
|DK33 | | | | |
| No. samples |20 |19 |17 |36 |
| Mean value |1.37 |1.51 |.88 |.20 |
| Std.dev. |.5 |.8 |.5 |.1 |
| Minimum |.69 |.19 |.49 |.09 |
| Maximum |2.36 |3.41 |2.65 |.43 |
|HU2 | | | | |
| No. samples |21 |9 |9 |9 |
| Mean value |1.40 |1.22 |.23 |.45 |
| Std.dev. |.6 |.8 |.1 |.2 |
| Minimum |.54 |.57 |.15 |.27 |
| Maximum |3.05 |3.16 |.38 |.79 |
|IT4 | | | | |
| No. samples |20 |20 |20 |20 |
| Mean value |3.52 |2.07 |.58 |.45 |
| Std.dev. |.2 |1.2 |.2 |.2 |
| Minimum |1.88 |.12 |.24 |.12 |
| Maximum |6.83 |4.30 |1.04 |.91 |
|NO1 | | | | |
| No. samples |21 |21 |21 |21 |
| Mean value | .32 |.39 |.20 |.07 |
| Std.dev. |.2 |.5 |.1 |.1 |
| Minimum |.08 |.05 |.08 |-.13 |
| Maximum |.74 |2.15 |.72 |.31 |
|RU14 | | | | |
| No. samples |6 |5 |5 |5 |
| Mean value |1.46 |.13 |.03 |.04 |
| Std.dev. |.3 |.1 |.0 |.0 |
| Minimum |.88 |.05 |.02 |.02 |
| Maximum |.86 |.31 |.06 |.05 |
Table 1.1 contd.
|Sampling period |NH3-N |NH4-N |NO3-N |HNO3-N |
| |(µg/m3) |(µg/m3) |(µg/m3) |(µg/m3) |
|SE2 | | | | |
| No. samples |21 |21 |22 |22 |
| Mean value | .16 |.70 |.30 |.16 |
| Std.dev. |.1 |.7 |.2 |.1 |
| Minimum |.05 |.12 |.04 |.04 |
| Maximum |.31 |2.61 |.69 |.50 |
|SE12 | | | | |
| No. samples |19 |19 |19 |19 |
| Mean value | .06 |.28 |.06 |.06 |
| Std.dev. |.0 |.2 |.0 |.0 |
| Minimum |.02 |.00 |.01 |.01 |
| Maximum |.13 |.88 |.16 |.19 |
| | | | | |
|4th period | | | | |
|FI9 | | | | |
| No. samples |30 |30 |28 |28 |
| Mean value | .04 |.19 |.03 |.02 |
| Std.dev. |.0 |.3 |.1 |.1 |
| Minimum |-.01 |-.01 |-.03 |-.03 |
| Maximum |.14 |1.36 |.23 |.16 |
|HU2 | | | | |
| No. samples |17 |9 |9 |9 |
| Mean value |.88 |1.04 |.32 |.32 |
| Std.dev. |.3 |.3 |.2 |.1 |
| Minimum |.33 |.43 |.08 |.17 |
| Maximum |1.49 |1.51 |.61 |.55 |
|IT4 | | | | |
| No. samples |20 |20 |20 |20 |
| Mean value |3.53 |1.55 |.42 |.27 |
| Std.dev. |.9 |.8 |.2 |.2 |
| Minimum |1.94 |.42 |.12 |.09 |
| Maximum |5.09 |2.99 |.84 |.72 |
|NO1 | | | | |
| No. samples |21 |21 |21 |21 |
| Mean value | .25 |.43 |.25 |.03 |
| Std.dev. |.2 |.4 |.2 |.0 |
| Minimum |.08 |.05 |.08 |-.09 |
| Maximum |.71 |1.72 |.95 |.12 |
|RU14 | | | | |
| No. samples | |20 |19 | |
| Mean value |. |2.06 |.09 |. |
| Std.dev. |. |7.7 |.1 |. |
| Minimum |. |.06 |.03 |. |
| Maximum |. |34.69 |.60 |. |
|SE2 | | | | |
| No. samples |21 |21 |21 |21 |
| Mean value | .13 |.76 |.27 |.08 |
| Std.dev. |.1 |.9 |.5 |.1 |
| Minimum | |.27 | | |
| Maximum |.37 |3.86 |1.83 |.36 |
|SE12 | | | | |
| No. samples |16 |15 |10 |17 |
| Mean value | .02 |.39 |.15 |.05 |
| Std.dev. | .0 |.5 |.2 |.0 |
| Minimum |-.01 |.12 |.02 |.01 |
| Maximum |.03 |1.99 |.63 |.14 |
| | | | | |
|5th period | | | | |
|DK33 | | | | |
| No. samples |6 |7 |4 |4 |
| Mean value |.51 |2.32 |.80 |.16 |
| Std.dev. |.4 |.8 |.4 |.1 |
| Minimum |.04 |1.22 |.48 |.11 |
| Maximum |1.03 |3.47 |1.39 |.22 |
Table 1.1 contd.
|Sampling period |NH3-N |NH4-N |NO3-N |HNO3-N |
| |(µg/m3) |(µg/m3) |(µg/m3) |(µg/m3) |
|NO1 | | | | |
| No. samples |21 |21 |21 |21 |
| Mean value | .16 |.25 |.18 |.04 |
| Std.dev. |.2 |.5 |.3 |.0 |
| Minimum |.02 |.04 |.02 |-.01 |
| Maximum | .65 |1.98 |1.27 |.12 |
|SE12 | | | | |
| No. samples |15 |8 |11 |13 |
| Mean value | .04 |.67 |.09 |.10 |
| Std.dev. |.1 |.4 |.1 |.1 |
| Minimum |.03 |.25 |-.06 |.02 |
| Maximum |.17 |1.22 |.27 |.30 |
| | | | | |
|6th period | | | | |
|CH2 | | | | |
| No. samples |21 |21 |21 |21 |
| Mean value |2.03 |1.76 |1.08 |.04 |
| Std.dev. |.6 |2.1 |1.2 |.0 |
| Minimum |.35 |.05 |.10 | |
| Maximum |5.57 |7.89 |4.02 |.11 |
| | | | | |
|7th period | | | | |
|DK33 | | | | |
| No. samples |17 |18 |23 |17 |
| Mean value |1.08 |6.52 |2.90 |.15 |
| Std.dev. |.5 |6.1 |3.1 |.1 |
| Minimum |.38 |.64 |.50 | |
| Maximum |1.85 |17.85 |10.25 |.44 |
|IT4 | | | | |
| No. samples |20 |20 |20 |20 |
| Mean value |2.14 |3.23 |1.89 |.45 |
| Std.dev. |.0 |2.0 |1.6 |.3 |
| Minimum |.78 |.29 |.15 |.06 |
| Maximum |.96 |6.38 |6.50 |.99 |
|SE2 | | | | |
| No. samples |1 |1 |1 |1 |
| Mean value | .44 |.16 |.05 | |
| Std.dev. |. |. |. |. |
| Minimum |.44 |.16 |.05 | |
| Maximum |.44 |.16 |.05 | |
Appendix 2
Denuder and filter summaries
Table 2.1: Overview of measurement results.
|Sampling period |NH3/NH4+ |HNO3/NO3 |NH4+NH3 (µg |NO3+HNO3 (µg |NH4 in |NO3 in |NO2-N |NH3/NH4 (µg |
| |(µg/m3) |(µg/m3) |N/m3), |N/m3), |precip. |precip. (mg |(µg N/m3) |N/m3) |
| | | |impreg. |impreg. |(mg N/l) |N/l) | | |
| | | |filter |filter | | | | |
|1st period | | | | | | | | |
|DK33 | | | | | | | | |
| No. samples | |8 | | | | | | |
| Mean value | |1.30 |. |. |. |. |. |. |
| Std.dev. | |.5 |. |. |. |. |. |. |
| Minimum | | .70 |. |. |. |. |. |. |
| Maximum | |2.29 |. |. |. |. |. |. |
|HU2 | | | | | | | | |
| No. samples |20 |10 | | |7 |7 | | |
| Mean value |1.82 |1.20 |. |. |.53 |.38 |. |. |
| Std.dev. |1.7 |.4 |. |. |.2 |.2 |. | |
| Minimum |.22 |.61 |. |. |.26 |.21 |. |. |
| Maximum |6.91 |1.82 |. |. |.87 |.79 |. |. |
|IT4 | | | | | | | | |
| No. samples |20 |20 | | | |6 |20 |15 |
| Mean value |4.90 |1.48 |. |. |. |3.06 |43.95 |.87 |
| Std.dev. |2.1 |1.2 |. |. |. |3.0 |22.2 |.5 |
| Minimum |2.12 |.11 |. |. |..80 |10.20 |.38 | |
| Maximum |10.18 |4.10 |. |. |.7.97 |99.40 |1.70 | |
|NO1 | | | | | | | | |
| No. samples |21 |21 | | | | | | |
| Mean value |.43 |.26 |. |. |. |. |. |. |
| Std.dev. |.4 |.3 |. |. |. |. |. |. |
| Minimum |.07 |.02 |. |. |. |. |. |. |
| Maximum |1.86 |1.09 |. |. |. |. |. |. |
|RU14 | | | | | | | | |
| No. samples |4 |6 | | | | | |6 |
| Mean value |.47 |.20 |. |. |. |. |1.39 |. |
| Std.dev. |.2 |.2 |. |. |. |. |.4 |. |
| Minimum |.17 |.07 |. |. |. |. |.75 |. |
| Maximum |.65 |.49 |. |. |. |. |1.95 |. |
|SE2 | | | | | | | | |
| No. samples |22 |22 |22 |21 |11 |11 |21 | |
| Mean value |1.07 |.72 |.99 |.68 |.49 |.82 |5.80 |. |
| Std.dev. |1.1 |.7 |.9 |.6 |.2 |.4 |3.0 |. |
| Minimum |.13 |.04 |.08 |.10 |.09 |.22 |2.30 |. |
| Maximum |4.43 |2.61 |3.97 |2.19 |.72 |1.31 |15.30 | |
| | | | | | | | | |
|2nd period | | | | | | | | |
|CH2 | | | | | | | | |
| No. samples |7 |16 |20 |21 |3 |3 |14 |21 |
| Mean value |3.79 |1.00 |5.73 |1.02 |1.41 |.81 |4.49 | |
| Std.dev. |2.4 |.5 |2.4 |.4 |.9 |.5 |1.8 |.0 |
| Minimum |1.51 |.25 |1.60 |.30 |.82 |.32 |1.20 | |
| Maximum |8.56 |1.84 |9.80 |2.00 |2.50 |1.33 |7.90 | |
|DE7 | | | | | | | | |
| No. samples |21 |19 | | |2 |2 |21 | |
| Mean value |.57 |1.07 |. |. |1.52 |4.19 |4.97 |. |
| Std. dev. |.3 |.8 |. |. |.5 |2.6 |1.6 |. |
| Minimum |.19 |.20 |. |. |1.14 |2.32 |2.60 |. |
| Maximum |1.21 |2.59 |. |. |1.90 |6.06 |10.10 |. |
|DK33 | | | | | | | | |
| No. samples |21 |13 | | | | | | |
| Mean value |4.94 |1.76 |. |. |. |. |. |. |
| Std.dev. |2.5 |.8 |. |. |. |. |. |. |
| Minimum |1.27 |.80 |. |. |. |. |. |. |
| Maximum |10.21 |3.01 |. |. |. |. |. |. |
|FI9 | | | | | | | | |
| No. samples |20 |20 |20 |19 |20 |20 |18 | |
| Mean value |.78 |.61 |.62 |.52 |.19 |.18 |1.44 |. |
| Std.dev. |.5 |.3 |.5 |.3 |.7 |.6 |.8 |. |
| Minimum |.15 |-.03 |.09 |.14 | | |.31 |. |
| Maximum |2.14 |1.09 |1.81 |1.09 |3.14 |2.78 |3.45 | |
Table 2.1 contd.
|Sampling period |NH3/NH4+ |HNO3/NO3 |NH4+NH3 (µg |NO3+HNO3 (µg |NH4 in |NO3 in |NO2-N |NH3/NH4 (µg |
| |(µg/m3) |(µg/m3) |N/m3), |N/m3), |precip. |precip. (mg |(µg N/m3) |N/m3) |
| | | |impreg. |impreg. |(mg N/l) |N/l) | | |
| | | |filter |filter | | | | |
|HU2 | | | | | | | | |
| No. samples |19 |9 | | |5 |5 | | |
| Mean value |1.81 |.73 |. |. |1.27 |.77 |. |. |
| Std.dev. |.8 |.1 |. |. |.8 |.6 |. |. |
| Minimum |.43 |.54 |. |. |.33 |.23 |. |. |
| Maximum |2.99 |.95 |. |. |2.17 |1.64 |. |. |
|NO1 | | | | | | | | |
| No. samples |20 |20 | | | | | | |
| Mean value |1.47 |.74 |. |. |. |. |. |. |
| Std.dev. |1.2 |.7 |. |. |. |. |. |. |
| Minimum |.09 |.12 |. |. |. |. |. |. |
| Maximum |4.17 |2.59 |. |. |. |. |. |. |
|RU14 | | | | | | | | |
| No. samples |6 |6 | | | | |6 | |
| Mean value |1.89 |.19 |. |. |. |. |.94 |. |
| Std.dev. |.9 |.1 |. |. |. |. |.3 |. |
| Minimum |.87 |.11 |. |. |. |. |.57 |. |
| Maximum |2.89 |.31 |. |. |. |. |1.23 |. |
|SE2 | | | | | | | | |
| No. samples |21 |21 |21 |20 |3 |4 |21 | |
| Mean value |1.59 |.96 |2.12 |.80 |2.97 |2.28 |6.64 | |
| Std.dev. |1.1 |1.0 |1.4 |.8 |2.1 |.3 |3.5 |. |
| Minimum |.25 |.02 |.35 |.13 |1.55 |1.99 |1.90 |. |
| Maximum |4.40 |3.06 |4.39 |3.08 |5.39 |2.67 |14.70 |. |
|SE12 | | | | | | | | |
| No. samples |15 |17 | | | | |17 | |
| Mean value |.85 |.21 |. |. |. |. |1.00 |. |
| Std.dev. |.7 |.1 |. |. |. |. |.3 |. |
| Minimum |.13 |.04 |. |. |. |. |.53 |. |
| Maximum |1.91 |.47 |. |. |. |. |1.63 |. |
| | | | | | | | | |
|3rd period | | | | | | | | |
|CH2 | | | | | | | | |
| No. samples |33 |21 |28 |28 |13 |12 |29 |35 |
| Mean value |3.63 |.49 |3.50 |.63 |.66 |.43 |3.62 |.03 |
| Std.dev. |1.7 |.3 |1.5 |.3 |.4 |.2 |1.2 |.0 |
| Minimum |.64 |.12 |1.00 |.20 |.20 |.17 |1.20 |.01 |
| Maximum |6.42 |1.17 |6.20 |1.20 |1.37 |.75 |6.40. |06 |
|DE7 | | | | | | | | |
| No. samples |21 |15 | | |4 |4 |21 | |
| Mean value |.52 |.53 |. |. |.88 |4.23 |4.19 |. |
| Std. dev. |.3 |.2 |. |. |.5 |3.0 |1.0 |. |
| Minimum |.01 |.22 |. |. |.33 |1.54 |3.10 |. |
| Maximum |1.44 |1.00 |. |. |1.37 |8.52 |6.60 |. |
|DK33 | | | | | | | | |
| No. samples |19 |17 | | | | | | |
| Mean value |2.90 |1.12 |. |. |. |. |. |. |
| Std.dev. |1.0 |.6 |. |. |. |. |. |. |
| Minimum |1.39 |.69 |. |. |. |. |. |. |
| Maximum |4.76 |2.88 |. |. |. |. |. |. |
|HU2 | | | | | | | | |
| No. samples |21 |9 | | |6 |6 | | |
| Mean value |1.92 |.68 |. |. |1.05 |.85 |. |. |
| Std.dev. |.9 |.2 |. |. |.8 |.3 |. |. |
| Minimum |.91 |.51 |. |. |.02 |.60 |. |. |
| Maximum |4.65 |.98 |. |. |1.98 |1.36 |. |. |
|IT4 | | | | | | | | |
| No. samples |20 |20 | | | |7 |20 | |
| Mean value |5.59 |1.03 |. |. |. |5.93 |22.03 |. |
| Std.dev. |1.9 |.4 |. |. |. |2.7 |3.3 |. |
| Minimum |2.95 |.36 |. |. |. |3.19 |16.40 |. |
| Maximum |11.04 |1.81 |. |. |. |10.90 |28.20 |. |
Table 2.1 contd.
|Sampling period |NH3/NH4+ |HNO3/NO3 |NH4+NH3 (µg |NO3+HNO3 (µg |NH4 in |NO3 in |NO2-N |NH3/NH4 (µg |
| |(µg/m3) |(µg/m3) |N/m3), |N/m3), |precip. |precip. (mg |(µg N/m3) |N/m3) |
| | | |impreg. |impreg. |(mg N/l) |N/l) | | |
| | | |filter |filter | | | | |
|NO1 | | | | | | | | |
| No. samples |21 |21 | | | | | | |
| Mean value |.71 |.28 |. |. |. |. |. |. |
| Std.dev. |.6 |.2 |. |. |. |. |. |. |
| Minimum |.25 |.10 |. |. |. |. |. |. |
| Maximum |2.62 |.78 |. |. |. |. |. |. |
|RU14 | | | | | | | | |
| No. samples |5 |4 | | | | |6 | |
| Mean value |1.56 |.07 |. |. |. |. |.63 |. |
| Std.dev. |.4 |.0 |. |. |. |. |.2 |. |
| Minimum |.95 |.06 |. |. |. |. |.43 |. |
| Maximum |2.01 |.08 |. |. |. |. |.88 |. |
|SE2 | | | | | | | | |
| No. samples |21 |22 |22 |22 |9 |9 |22 | |
| Mean value |.86 |.46 |.96 |.40 |1.30 |.89 |2.81 |. |
| Std.dev. |.7 |.3 |.7 |.2 |1.7 |.9 |1.3 |. |
| Minimum |.27 |.08 |.39 |.07 |.21 |.19 |1.26 |. |
| Maximum |2.66 |.97 |2.84 |.76 |5.75 |3.06 |6.15 | |
|SE12 | | | | | | | | |
| No. samples |19 |19 | | | | |19 | |
| Mean value |.34 |.11 |. |. |. |. |.59 |. |
| Std.dev. |.2 |.1 |. |. |. |. |.2 |. |
| Minimum |.02 |.02 |. |. |. |. |.33 |. |
| Maximum |.96 |.34 |. |. |. |. |.95 |. |
| | | | | | | | | |
|4th period | | | | | | | | |
|DE7 | | | | | | | | |
| No. samples |19 |13 | | |6 |6 |19 | |
| Mean value |.18 |.87 |. |. |1.17 |2.98 |5.28 |. |
| Std. dev. |.2 |.6 |. |. |1.1 |.7 |2.1 |. |
| Minimum |.01 |.23 |. |. |.19 |2.48 |1.70 |. |
| Maximum |.65 |2.22 |. |. |3.22 |4.31 |10.90 |. |
|FI9 | | | | | | | | |
| No. samples |30 |28 |30 |30 |6 |6 |30 | |
| Mean value |.24 |.08 |.27 |.21 |.06 |.22 |3.63 |. |
| Std.dev. |.3 |.1 |.3 |.1 |.1 |.1 |1.0 |. |
| Minimum |-.01 |-.03 |.07 |.05 |.00 |.02 |1.91 |. |
| Maximum |1.36 |.33 |1.25 |.76 |.17 |.43 |6.24 | |
|HU2 | | | | | | | | |
| No. samples |18 |9 | | |2 |2 | | |
| Mean value |1.35 |.64 |. |. |.67 |.43 |. |. |
| Std.dev. |.7 |.2 |. |. |.4 |.2 |. |. |
| Minimum |.49 |.27 |. |. |.36 |.28 |. |. |
| Maximum |2.59 |1.03 |. |. |.97 |.58 |. |. |
|IT4 | | | | | | | | |
| No. samples |20 |20 | | | |5 |20 |18 |
| Mean value |5.08 |.69 |. |. |. |9.02 |22.03 |.54 |
| Std.dev. |1.3 |.3 |. |. |. |5.5 |3.3 |.2 |
| Minimum |2.46 |.22 |. |. |. |2.70 |16.40 |.24 |
| Maximum |7.67 |1.33 |. |. |. |14.80 |28.20 |.85 |
|NO1 | | | | | | | | |
| No. samples |21 |21 | | | | | | |
| Mean value |.68 |.28 |. |. |. |. |. |. |
| Std.dev. |5 |.3 |. |. |. |. |. |. |
| Minimum |.23 |.09 |. |. |. |. |. |. |
| Maximum |2.20 |1.05 |. |. |. |. |. |. |
|RU14 | | | | | | | | |
| No. samples |16 |14 | | | | |20 | |
| Mean value |1.27 |.11 |. |. |. |. |.76 |. |
| Std.dev. |7 |.2 |. |. |. |. |.3 |. |
| Minimum |.55 |.01 |. |. |. |. |.30 |. |
| Maximum |2.61 |.63 |. |. |. |. |1.60 |. |
Table 2.1 contd.
|Sampling period |NH3/NH4+ |HNO3/NO3 |NH4+NH3 (µg |NO3+HNO3 (µg |NH4 in |NO3 in |NO2-N |NH3/NH4 (µg |
| |(µg/m3) |(µg/m3) |N/m3), |N/m3), |precip. |precip. (mg |(µg N/m3) |N/m3) |
| | | |impreg. |impreg. |(mg N/l) |N/l) | | |
| | | |filter |filter | | | | |
|SE2 | | | | | | | | |
| No. samples |21 |21 |21 |21 |7 |7 |20 | |
| Mean value |.88 |.35 |.93 |.39 |.78 |.65 |1.20 |. |
| Std.dev. |8 |.6 |1.1 |.5 |.9 |.5 |.7 |. |
| Minimum |.40 | |.22 |.04 |.02 |.13 |.48 |. |
| Maximum |3.91 |2.19 |4.72 |2.00 |2.14 |1.36 |2.62 | |
|SE12 | | | | | | | | |
| No. samples |13 |10 | | | | | | |
| Mean value |.45 |.20 |. |. |. |. |. |. |
| Std.dev. |6 |.2 |. |. |. |. |. |. |
| Minimum |.14 |.04 |. |. |. |. |. |. |
| Maximum |2.01 |.77 |. |. |. |. |. |. |
| | | | | | | | | |
|5th period | | | | | | | | |
|DK33 | | | | | | | | |
| No. samples |6 |2 | | | | | | |
| Mean value |2.64 |1.15 |. |. |. |. |. |. |
| Std.dev. |6 |.6 |. |. |. |. |. |. |
| Minimum |1.78 |.72 |. |. |. |. |. |. |
| Maximum |3.25 |1.59 |. |. |. |. |. |. |
|NO1 | | | | | | | | |
| No. samples |21 |21 | | | | | | |
| Mean value |.41 |.22 |. |. |. |. |. |. |
| Std.dev. |6 |.3 |. |. |. |. |. |. |
| Minimum |.06 |.02 |. |. |. |. |. |. |
| Maximum |2.04 |1.29 |. |. |. |. |. |. |
|SE12 | | | | | | | | |
| No. samples |6 |10 | | | | | | |
| Mean value |.77 |.21 |. |. |. |. |. |. |
| Std.dev. |4 |.2 |. |. |. |. |. |. |
| Minimum |.27 |.04 |. |. |. |. |. |. |
| Maximum |1.26 |.57 |. |. |. |. |. |. |
| | | | | | | | | |
|6th period | | | | | | | | |
|CH2 | | | | | | | | |
| No. samples |21 |21 | | | | | | |
| Mean value |3.79 |1.12 |. |. |. |. |. |. |
| Std.dev. |.4 |1.1 |. |. |. |. |. |. |
| Minimum |.54 |.14 |. |. |. |. |. |. |
| Maximum |12.16 |4.03 |. |. |. |. |. |. |
| | | | | | | | | |
|7th period | | | | | | | | |
|DK33 | | | | | | | | |
| No. samples |17 |11 | | | | | | |
| Mean value |7.19 |2.91 |. |. |. |. |. |. |
| Std.dev. |.3 |3.0 |. |. |. |. |. |. |
| Minimum |1.20 |.60 |. |. |. |. |. |. |
| Maximum |19.59 |10.25 |. |. |. |. |. |. |
|IT4 | | | | | | | | |
| No. samples |20 |20 | | | |2 |20 | |
| Mean value |5.37 |2.34 |. |. |. |14.03 |30.87 |. |
| Std.dev. |.3 |1.7 |. |. |. |12.1 |11.6 |. |
| Minimum |2.11 |.23 |. |. |. |5.45 |10.20 |. |
| Maximum |9.02 |7.49 |. |. |. |22.60 |47.60 |. |
|SE 02 | | | | | | | | |
| No. samples |1 |1 |1 |1 | | |1 | |
| Mean value |.60 |.05 |.91 |.08 |. |. |2.40 |. |
| Std.dev. |. |. |. |. |. |. |. |. |
| Minimum |.60 |.05 |.91 |.08 |. |. |2.40 |. |
| Maximum |.60 |.05 |.91 |.08 |. |. |2.40 |. |
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