Acid aerosol measurements at a suburban Connecticut site

Abstract

Abstract Atmospheric acidity data were gathered during a year-long field project investigating the possible health effects of acid aerosol in a rural community in southwestern Connecticut. This site was chosen because the air quality is frequently influenced by pollutants transported from the New York-New Jersey corridor as well as from the Midwest U.S. An annular denuder filter-pack system utilized to obtain daily measurements of gaseous HNO 3 , HONO, SO 2 , and NH 3 ; plus fine particle SO 4 2− , NO 3 − , and H + . Fine particle mass ( d ⩽ 2.1 μm ) and PM10 (particles d ⩽ 10 μm ) were also measured. Ozone concentrations and basic meteorological data were also obtained continuously. The atmosphere was acidic with average concentrations of HONO (16 nmol m –3 ), HNO 3 (42 nmol m −3 ), and H + (42 nmol m −3 ), observed from May to September 1988. Atmospheric ammonia concentrations were fairly low averaging 34 nmol m −3 during the same period, and suggesting the neutralizing capacity of the air was significant to neutralize all the acidic species present. Neutralization of acidic particles by reactions on the filter media after collection resulted in a loss of approximately 10% of the measured particle strong acidity for the summertime period investigated. Concentrations of ozone and acidic gases tended to peak with mixed layer flow from the south-southwest while particulate acidity was highest with flow predominantly from the west-soutwest. Hourly ozone concentrations greater than 100 ppb were observed on 31 different days during the monitoring, and concentrations greater than 150 ppb measured on 14 days. HNO 3 and aerosol strong acidity (H + ) concentrations reached 174 and 199 nmol m −3 , respectively during the summer months.