The Use of Ambient Measurements To Identify which Precursor Species Limit Aerosol Nitrate Formation

Abstract

A thermodynamic equilibrium model was used to investigate the response of aerosol NO 3 to changes in concentrations of HNO 3 , NH 3 , and H 2 SO 4 . Over a range of temperatures and relative humidities (RHs), two parameters provided sufficient information for indicating the qualitative response of aerosol NO 3 . The first was the excess of aerosol NH 4 + plus gas-phase NH 3 over the sum of HNO 3 , particulate NO 3 , and particulate SO 4 2-concentrations. The second was the ratio of particulate to total NO 3 concentrations. Computation of these quantities from ambient measurements provides a means to rapidly analyze large numbers of samples and identify cases in which inorganic aerosol NO 3 formation is limited by the availability of NH 3 . Example calculations are presented using data from three field studies. The predictions of the indicator variables and the equilibrium model are compared.

Processes Influencing Secondary Aerosol Formation in the San Joaquin Valley during Winter

“…The prevalence of ambient NH 3 concentrations in excess of ambient nitric acid concentrations at these three sites is consistent with findings from the IMS95 (where Ͼ90% of samples were NH 3 rich) 6,48 and from regional modeling studies. 49 The CRPAQS data show an eightfold gradient in NH 3 concentration and a twofold gradient in nitric acid concentration between the middle of the SJV, represented by Angiola, and the foothills, represented by Sierra Nevada Foothills.…”

Differences between Weekday and Weekend Air Pollutant Levels in Southern California

“…The samples that are thought to be furthest from equilibrium were excluded from the analysis. 39,45 Nearly all samples showed that particulate NO 3 Ϫ concentrations would decrease in response to a 20% reduction of HNO 3 ; in many cases, the predicted decrease was close to 20% ( Figure 8 sites, the mean Sunday NMHC was 3% lower than the mean weekday NMHC at the times of peak O 3 , and 16 -30% lower at other times. Twenty of 28 SoCAB sites (28 of 78 total sites) showed statistically significant (p Ͻ 0.01) higher mean Sunday than weekday O 3 levels; 49 of the remaining 50 sites showed no significant differences between mean weekday and Sunday peak O 3 levels.…”

“…40 -44 in conjunction with examination of the ambient measurements. 39 Here, the measurements from the 1-yr PTEP study are analyzed.…”

Chemical characteristics of inorganic ammonium salts in PM<sub>2.5</sub> in the atmosphere of Beijing (China)

“…The slope of this regression line was 1.65, indicating an excellent ion balance and the presence on Nylon filters of NH 4 NO 3 and NH 4 Cl as constituent of the total fine particles. In addition, using the approach of Ansari and Pandis (1998) and of Blanchard et al (2000) it is possible to calculate the excess NH 3 , which represents the quantity of NH 3 that would remain after complete neutralization of available aerosol and acid gases, is defined as:…”