Measurements of PM10 aerosol and gas-phase nitrous acid during fall season in a semi-urban atmosphere

Abstract

Abstract Simultaneous measurements of PM 10 (particle mass) aerosol and gas-phase nitrous acid (HNO 2 ) were made over a fall season at a semi-urban site, Kwangju, South Korea, to investigate the effects of agricultural waste burning on their concentrations. The PM 10 aerosol and gaseous species samples were collected three times a day for 6- and 12-h durations using a three-stage filter pack during three intensive sampling campaigns, and analyzed for particulate mass, ionic species, and HNO 3 concentrations. Hourly HNO 2 measurements were also made using a dual channel glass-coil sampling technique and ion chromatography analysis. NO 2 (g) was measured using a differential optical absorption spectroscopy (DOAS) to investigate the formation pathway of HNO 2 . PM 10 , K + , and Cl − concentrations during the agricultural wastes burning event were substantially higher than during any other sampling periods, whereas the concentrations of secondary-formed aerosols, i.e., NO 3 − , NH 4 + , and SO 4 2− , were substantially low during the burning event, compared to those in the non-burning periods. Higher HNO 2 concentrations occurred during the night and November sampling periods when PM 10 mass concentrations were generally high, and lower mixing layer and more humid condition were found, rather than during the day, September, and October sampling periods. It was also found that rapid increase in HNO 2 levels from 0.2 to 2.6 ppb in the afternoon on October 20 was due to direct emissions from the agricultural wastes (straw and stubble) burning practice. Increases in the HNO 2 /NO 2 ratio after sunset, and a close relationship between HNO 2 /NO 2 and the PM 10 mass indicate that during the study period NO 2 is the precursor of HNO 2 production at nighttime.