Acquisition of Regional Air Quality Model Validation Data for Nitrate, Sulfate, Ammonium Ion and Their Precursors

Abstract

An intensive field study was conducted throughout California's South Coast Air Basin to acquire air quality model validation data for use with aerosol nitrate formation models. Aerosol nitrate, sulfate, ammonium, other major ionic aerosol species, nitric acid gas and ammonia were measured concurrently at ten sites for forty-eight consecutive hours during the period August [30][31] 1982. Ozone, NO and NO were measured at all locations, and PAN was measured at Pasadena an~ Riverside, completing a nitrogen balance on the air masses studied.The product of the meas~red nitric acid and ammon~a concentrations ranged from less than 1 ppbv to greater than 300 ppbv during the experiment, providing a wide range of conditions over which comparisons can be drawn between chemical equilibrium calculations and experimental results. The ionic material in the aerosol phase was chemically more complex than is assumed by present theoretical models for the equilibrium between NH 3 , HNOa and the aerosol phase, and included . .f.f N + ++ ++ + d Cl-. dd . . NH+ s1gn1 1cant amounts o a , a , Mg , K an 1n a 1t1on to 4 , so4 and NO)· Results of the experiment showed that aerosol nitrate levels in excess of 20 ~g m-3 accumulated in near-coastal locations in the morning of August 31, followed by subsequent transport across the air basin. Trajectory analysis showed that the afternoon aerosol nitrate peak observed inland at Rubidoux near Riverside was associated with the same air mass that contained the high morning nitrate levels near the coast, indicating that description of both transport and atmospheric chemical reactions is important in understanding regional nitrate dynamics. , 1977;Cass, 1979;Groblicki et al., 1981 Environmental Protection Agency (1973, 1978 et seq.). PAN was measured by electron capture gas chromatography, and NO and N0 2 were measured by chemiluminescence by researchers at the University of California at Riverside (UCR). PAN also was measured by the same principle at Caltech in Pasadena.The aerosol, nitric acid and ammonia sampling apparatus for this experiment is shown schematically in Figure 2. Aerosol nitrate and nitric acid concentrations were measured both by dual filter methods and by the denuder difference method. Gaseous ammonia was measured by a dual filter method using oxalic acid impregnated filters as a sink for NH 3 • Filter holders were of open-faced design so that any large particle nitrates would be collected. The sampling apparatus was surrounded by a bug screen and shaded by a sun shield to prevent nitrate volatilization through over-heating. Nine of the ten sampling sites shown in Figure 1 were equipped as indicated in Figure 2, while the lOth site at Riverside (UCR) consisted of only the two sampling lines that contained dual filter packs.In the dual filter method for nitric acid determination, a1r was drawn at a rate of 10 lpm through a dual filter pack (Grosjean, 1983;Spicer et al., 1982;Appel et al., 1980). A teflon prefilter (Membrana, Zefluor, 47 mm diameter, 1 ~m pore size) first ...

Ammonia and Nitric Acid Concentrations in Equilibrium With Atmospheric Aerosols: Experiment vs Theory

“…Results from the present experiment show that the ionic portion of the bulk aerosol contains all of the above, plus sodium, potassium, calcium and chloride ions {see Figures 4 and 5 of Russell and Cass, 1984).…”

“…locations in southern California (Figure 1) over a 48-hour period. The details of the experiment are described by Russell and Cass (1984), and only will be summarized here.…”

“…Data on aerosol speciation at these sites are presented elsewhere (Russell and Cass, 1984). The Long Beach sampling station, which is located about 6 km from the Pacific Ocean, experienced lower temperatures (down to 18°C) and higher relative humidities In the first of the two external mixture cases considered, all of the aerosol nitrate is assumed to be present as ammonium nitrate.…”

Airshed Calculation of the Sensitivity of Pollutant Formation to Organic Compound Classes and Oxygenates Associated with Alternative Fuels

“…Pollutant measurements of trace species, including PAN, HNO3, aerosol nitrate, and NH 3 , were made during the first two days of the period. 9 Along with routine monitoring data, this allowed for extensive model performance testing. Model results for not only O3 and NO2, but also trace species such as nitrate and PAN compared well with measurements.…”

Chemical Characteristics of PM10Aerosols Collected in the Los Angeles Area

“…Nitric acid is produced during daylight hours by hydroxyl radical attack on NO2, and at night by chemical reactions involving the nitrate radical and N2O5. 21 Rubidoux is far enough downwind of the major industrial and urban pollution sources to experience high total inorganic nitrate (HNO3 + aerosol nitrate) levels and is also directly downwind of a large, sharply defined source of fresh NH3 emissions from agricultural activities 12 ' 20 (also see the NH3 emission pattern in Figure 6 of Reference 22). NH4NO3 production occurs when ammonia or HNO3 is introduced into an air parcel in amounts above that needed for the concentration product of HNO3 times NH 3 to equal the equilibrium dissociation constant for NH4NO3.…”