Filter Pack Sampling Research Articles

Sampling artifacts in the determination of particulate sulfate and SO2(g) in the desert Southwest using filter pack samplers

Particles collected in the desert Southwest on Teflon filters using an annular denuder sampling system absorb SO 2 (g) in a subsequential exposure to SO 2 (g) in the laboratory if the concentration of fine particulate sulfate measured with a filter pack sampling system is greater than the concentration of sulfate measured with the annular denuder sampling system. If the concentrations of sulfate determined using the two sampling systems agreed, no absorption of SO 2 (g) by the denuder-collected particles occurs. These results show that SO 2 (g) may be collected by Southwest desert fine particles during sampling, resulting in measured concentrations of fine particulate sulfate that are higher than the correct concentrations. The magnitude of this filter pack sampling artifact, 0.1-0.4 μg SO 4 2- /m 3 , is small. However, the artifact is important relative to the concentration of particulate sulfate present in the desert Southwest, typically 0.5-2 μg SO 4 2- /m 3 . The magnitude of the filter pack sulfate sampling artifact is not related to either the atmospheric particulate sulfate or SO 2 (g) concentrations.

A study of SO2, SO42− and trace elements in clear air and clouds above the Midwestern United States

In April and May 1990, as a part of ACID MODES II, a series of aerosol, gas and cloud water samples were collected over OH, WV, KY and IN at an altitude of 1.2–3 km using two aircraft. We report here the concentrations of SO2, SO42− and 12 trace elements measured on 41 filter pack samples collected over 17 flights and pH, conductivity, SO42− and selected trace elements in 17 cloud water samples from four flights. We discuss the composition of the airborne aerosols and cloud water above this area which is a major source region of SO2. Mean mixed layer concentrations of SO42− (μg m−3), and trace elements Zn, As, Se and Sb (ng m−1) were; 7.5±3.1, 35±19, 1.4±0.9, 1.7±0.8 and 0.49±0.22, respectively. These elements are primarily associated with submicron-sized aerosols and were the only elements measured that were significantly enriched relative to average crustal abundances. While the samples collected in the mixed layer had concentrations comparable to those at nearby surface sites, a 10-fold decrease in concentrations of all species was observed in samples collected immediately above the mixed layer. On average, 68% of the S was present as SO2 (average concentration in mixed layer air was 3.5 ppbv). A strong relationship was observed between total S and aerosol Se and to a lesser degree between As and Sb. The SO42−/Se tracer technique was used for the first time from an aircraft platform to determine in-cloud SOZ oxidation. Although the aircraft collected limited cloud water (generally col 20 ml) and small air volumes (< 10 m3), it is demonstrated that SO42− and Se can be determined with adequate uncertainty to apply the technique. In-cloud oxidation was found in three of the four clouds and accounted for up to 50% of the total SO42−. Examples of SO2 limited, and oxidant limited conditions were also observed.

Heterogeneous conversion contribution to the sulfate observed over Lake Michigan

It has been shown that sulfur dioxide (SO 2) to sulfate (SO 4 2−) heterogeneous conversion occurs by ozone (O 3) oxidation in the high pH water associated with coarse sea-salt particles over the oceans. To further investigate this conversion mechanism, aircraft-based coarse and fine particle filter pack sampling, O 3 and SO 2 real-time monitoring, and aerosol optical probe particle size spectra determinations were incorporated into measurements over the alkaline fresh waters of Lake Michigan during June and July 1991. Ion chromatography analysis of Teflon filters showed that one-third of the observed total SO 4 2−, with a mean value of 55 nmol SO 4 2− m −3; was present in coarse-mode, predominantly lake-derived particles. The sum of lake and soil particle sources contributed < 6 nmol SO 4 2− m −3 to the coarse-mode 55 nmol SO 4 2− m −3; cloud conversion and coagulation contributed < 5 nmol SO 4 2− m −3. The total of these sources contributed < 20% of the coarse-mode SO 4 2−, whereas O 3-oxidized SO 2 conversion in the water associated with coarse particles produced from 10 to > 55 nmol SO 4 2− m −3. Heterogeneous conversion of SO 2, when a few μg m −3 (or more) of buffered water is present in large particles, may produce sufficient SO 4 2− that it must be considered in boundary layer sulfur mass balance calculations and models.

Intercomparison of annular denuder and filter pack sampling methods for collection of acidifying species in south east England

Both annular denuder system (ADS) and filter pack (F.P) samplers exhibited a broad agreement. However, the F.P sampler collected higher concentrations of large particles reflecting better inlet characteristics. The F.P sampler also overestimated measurements of NH 3, HCl and HNO 3 primarily due to evaporation of ammonium chloride and ammonium nitrate to their precursor gases. Sulphate particles showed good accord in both samplers. It is very important to stress that these techniques may vary from one place to another.

Comparison of annular denuder and filter pack collection of HNO3 (g), HNO2((g), SO2 (g), and particulate-phase nitrate, nitrite and sulfate in the south-west desert

During the 15 January–4 February 1986 SCENES Special Study, a comparison study was conducted to determine atmospheric HNO3 (g), HNO2 (g), SO2 (g), and particle-phase nitrate, nitrite and sulfate sampled with annular diffusion denuder and filter pack sampling systems for 12-h periods. The results of the ion chromatographic analyses of the denuder and filter extracts from the annular denuder system showed that an average of 88% of the total nitrate measured was HNO3 (g), 97% of the total nitrite was HNO2 (g), and 91% of the total sulfur was present as SO2 (g). Analyses of the various gas-phase species collected by replicate annular denuder systems indicated that a precision of ± 3% to ± 18% was achieved using these denuders. The good agreement in HNO3 (g) concentrations observed between the filter pack and the denuder (r2=0.873, slope=1.06±0.03, intercept=0±3.5 nmol m−3) results from the fact that the majority of the atmospheric nitrate consisted of HNO3 (g), which minimized any positive artifact in HNO3(g) due to loss of HNO3(g) from particles collected in the filter pack. The particulate-phase nitrate correlation between the two sampling systems was not as good (r2=0.709, slope=0.519±0.045, intercept =0±1.2 nmol m−3) because the lower percentage of nitrate present as the particulate species was more affected by the loss of particulate nitrate during sampling with the filter pack.

Comparison of indoor and outdoor concentrations of acid gases, ammonia and their associated salts

Abstract The concentrations of ammonia and acid gases inscluding HCl, HNO3 and SO2 as well as their particulate salts were measured both inside and outside the buildings of the University of Essex, U.K., in summer, using diffusion denuder and filter pack samplers. Indoor and outdoor concentration relationships, in terms of the I/O ratios were 0.48 for HCl, 0.22 for HNO3 and SO2, 10.7 for NH3. The average I/O ratios of their particulate salts were 0.52 for Cl−,0.43 for NO3 −,0.81 for SO4 2− and 0.96 for NH4 +, respectively. The observed results showed that indoor concentrations correlate well with those outdoors, except for NH3. The concentrations of NH3 indoors were 3.5–21 times higher than those outdoors during the sampling period, indicating that for those pollutants with strong indoor sources there is little correlation between indoors and outdoors. Comparing the dissociation behaviour of volatile ammonium salts in the indoor and outdoor atmosphere, the concentration products indoors were rather lower ...

Field intercomparison of filter pack and denuder sampling methods for reactive gaseous and particulate pollutants

Atmospheric sulphate, nitrate, chloride and ammonium species have been measured with colocated filter pack and denuder samplers. In general the total amount of a species collected by the two types of sampler was almost the same, although there was evidence of better inlet efficiency for particles in the filter pack sampler. The filter pack gives slightly higher measurements of the volatile species HNO 3, HCl and NH 3 than the denuder, with a corresponding lower measure of particulate NO 3 −, Cl − and NH 4 +, attributable to volatilization of ammonium salts from the filter pack pre-filter. In the context of most ambient measurements, the divergences between the techniques are small, and it is argued that differences in these measurement techniques are inevitably site, operator and apparatus-specific and data from one site or research group cannot readily be extrapolated to other sites.

Field measurements of the dissociation of ammonium nitrate and ammonium chloride aerosols

Atmospheric concentrations of HNO 3, HCl and NH 3 have been measured at Essex, UK and Cabauw, The Netherlands, using both filter pack (Essex) and denuder (Cabauw) sampling methods and integration times of 3, 12 and 24 h. Comparisons of the concentration products [HNO 3] [NH 3] and [HCl] [NH 3] with the predictions of equilibrium chemical thermodynamics for a non-interactive external mixture of NH 4Cl and NH 4NO 3 show generally good agreement at temperatures above ca 5°C, and indicate that both aerosol salts are normally present at these sites. The ratio [HCl] [HNO 3] agrees well with theory at lower temperatures ( < ~ 5°C), but shows a significant excess of HNO 3 at higher temperatures. Reasons for deviations of measurements from theoretical predictions are discussed, although no firm conclusions are reached.

Seasonal variations in atmospheric SOx and NOy species in the adirondacks

This paper reports the results of over 2 years of measurements of several of the species comprising atmospheric SO x (= SO 2+ SO 4 2−) and NO y (= NO+ NO 2 + PAN + HNO 3+ NO 3 −+ organic nitrates + HONO + 2 N 2 O 5 …) at Whiteface Mountain, New York. Continuous real-time measurements of SO 2 and total gaseous NO y provided data for about 50% and 65% of the period, respectively, and 122 filter pack samples were obtained for HNO 3, SO 2 and aerosol SO 4 2−, NO 3 −, H + and NH 4 +. Concentrations of SO 2 and NO y were greatest in winter, whereas concentrations of the reaction products SO 4 2− and HNO 3were greatest in summer. The seasonal variation in SO 4 2− was considerably more pronounced than that of HNO 3and the high concentrations of SO 4 2− aerosol present in summer were also relatively more acidic than SO 4 2− aerosol in other seasons. As a result, SO 4 2− aerosol was the predominant acidic species present in summer, HNO 3was predominant in other seasons. Aerosol NO 3 − concentrations were low in all seasons and appeared unrelated to simultaneous NO y and HNO 3concentrations. These data are consistent with seasonal variations in photochemical oxidation rates and with existing data on seasonal variations in precipitation composition. The results of this study suggest that emission reductions targeted at the summer season might be a cost-effective way to reduce deposition of S species, but would not be similarly cost-effective in reducing deposition of N species. kwAcid deposition, seasonal variation, sulfate, nitrate, nitric acid, sulfur dioxide, oxides of nitrogen, hydrogen peroxide, ozone, air pollution, Adirondack Mountains

Comparison of six denuder methods and a filter pack for the collection of ambient HNO 3(g), HNO 2(g) and SO 2(g) in the 1985 NSMC study

The concentrations of HNO 2(g), HNO 2(g), particle nitrate and particle nitrite have been determined using annular denuders (AD), nylon denuders (ND), short nylon denuders (SD), tungstic acid denuders (TD), cylindrical carbonate denuders (CD), a filter pack (FP), and a denuder difference method (DD) in field tests during the 1985 NSMCS. Concentrations of SO 2(g) and particle sulfate were measured by the annular denuder (AD) and cylindrical carbonate denuder (CD) systems. The results of linear regression comparison of various collection methods for total nitrate, HNO 3(g) and HNO 2(g), and results calculated as the denuder difference between nitrate and nitrite collected on the FP sampler and on the filter pack after the AD are presented. Results for HNO 3(g) and particle nitrate measured by the different sampling systems compared well with the exception of the TD and CD systems. The AD, FP and SD samplers showed the best consistency in results presumably because they operate at higher flow rates and give more sample with correspondingly lower analytical errors. The results obtained for the nitrogenous species studied are also correlated with other atmospheric parameters which might be related to the formation of HNO 3(g) and/or HNO 2(g) in the atmosphere. Concentrations of SO 2(g) measured by the annular denuder (AD) are compared to values determined by flame photometry.

The nitric acid shootout: Field comparison of measurement methods

Eighteen instruments for measuring atmospheric concentrations of nitric acid were compared in an eight day field study at Pomona College, situated in the eastern portion of the Los Angeles Basin, in September 1985. The study design included collocated and separated duplicate samplers, and the analysis by each laboratory of a set of quality assurance filters, so that the experimental variability could be distinguished from differences due to measurement methods. For all sampling periods, the values for nitric acid concentrations reported by the different instruments vary by as much as a factor of four. The differences among measurement techniques increase with nitric acid loading, corresponding to a coefficient of variation of 40%. In contrast, samplers of the same design operated by the same group show variability of 11–27 %. Overall, the highest reported concentrations are observed with the filter packs and lower concentrations are observed by the annular denuders and tunable diode laser absorption spectrometers. When the nitric acid concentrations are high enough to be detected by the FTIR, the FTIR values are close to those obtained by the denuder difference method and to the mean value from the other sampler groups. In the absence of a reference standard for the entire study, measurement methods are compared to the average of four denuder difference method samplers (DDM). Filter pack samplers are higher than the DDM for both daytime and night-time sampling. Two different filter packs using Teflon® prefilters are higher than the DDM by factors of 1.25 and 1.4. The results from the three annular denuders do not agree; the ratios of means to the DDM value are 1.0,0.8 and 0.6. For the transition flow reactor method and for two dichotomous samplers operated as denuder difference samplers, the ratio of means to the DDM are 1.09 and 0.93, respectively. The tunable diode laser absorption spectrometers gave lower daytime and higher night-time readings compared to the DDM, especially during the last three days of the study. Averaged over the entire measurement period, the daytime ratio of TDLAS to DDM is 0.8 and the night-time ratio is 1.7.

Patterns of atmospheric nitrates, sulfate, and hydrogen chloride in the central Ohio River Valley over a one-year period

A study of the seasonal distribution of gaseous and particulate nitrate, sulfate, and hydrogen chloride in the central Ohio Valley is reported. The Ohio Valley has been identified as a significant source of the precursors to atmospheric acids which may be deposited hundreds of kilometers downwind from the source region. This study was undertaken to provide information on the concentration patterns of several species important in acidic deposition. Filter pack samples were collected for 24 h once each week (with some exceptions) from October 1979 through October 1980. The mean concentrations were: 4.05 μg/m 3 sulfate, 3.76 μg/m 3 total inorganic nitrate (TIN), 2.11 μg/m 3 particulate nitrate (apparent), and 1.65 μg/m 3 gaseous nitric acid (apparent). Other recent studies in the Ohio Valley yielded gaseous organic nitrate (PAN) concentrations of 2.3 μg/m 3 in the spring and 4.8 μg/m 3 in summer. Sulfate concentrations were highest in the summer, and both nitric acid and total inorganic nitrate levels were highest in spring and summer. The HNO 3/TIN ratio was also highest during warm weather. A limited number of samples were analyzed for gaseous hydrogen chloride. The concentration of HCl averaged 0.53 μg/m 3 over a 2-month period. On a molar basis, HCl and HNO 3 concentrations were nearly equivalent over the 2-month period, suggesting that more attention should be paid to the role of HCl in atmospheric deposition.