Ion concentrations in atmospheric aerosols: The influence of nitrogen oxides and ozone mixing ratios, local meteorology, and the lake breeze in Chicago, Illinois

Aerosols adversely affect local air quality and impact human health and climate. This is especially true of aerosols composed of sulfate and nitrate, which can form within the atmosphere through reactions involving the trace gases NOx (NO2 + NO) and ozone. The presence of these species in Chicago is not only dependent on vehicular and industrial emissions, but also on local meteorology including the lake breeze. The lake breeze allows air masses containing precursor pollutants residing above Lake Michigan to return back to the city possibly leading to increased pollution levels.; To study this effect, atmospheric aerosol samples were taken at the Loyola University Chicago air station (LUCAS) in the summers of 2002, 2003 and 2004. Particulates were collected onto quartz fiber filters twice a day from 0700h-1000h and from 1100h-1300h in order to determine pollutant levels before and after a lake breeze onset. Weather conditions, and ozone and NOx mixing ratios were monitored in parallel. After collection, particles were extracted from the filters and analyzed for inorganic anions and cations, and low molecular weight organic acids by ion chromatography. The method employed for determining ions in aerosols was validated by various experiments, which showed high filter collection and extraction efficiency, and good method repeatability and reproducibility.; The most abundant ions found in Chicago were sulfate, nitrate and ammonium However, the concentrations varied each summer study due to differences in overall temperatures and wind direction profiles. The formation of sulfate and nitrate was also investigated in regard to ammonium ratios, which showed dependence on wind direction and the lake breeze effect. A case study was used to further investigate the influence of trace gas mixing ratios and meteorology on ion concentrations. Four cases were distinguished in which sulfate, nitrate and oxalate concentrations varied depending upon weather parameters and ozone and NOx mixing ratios. Case 1 described days with conditions for the lowest ion concentrations and case 2 consisted of days with moderate ion concentrations, while days in case 3 showed conditions leading to a lake breeze and as a result, to elevated ion concentrations and case 4 was composed of days with the highest ion concentrations. The cases were validated by statistical analysis. Finally, methods were developed for determining the concentrations of gas phase ammonia and organic acids to complement results found for ion concentrations in Chicago.