Contrasting sources and processes of particulate species in haze days with low and high relative humidity in winter time Beijing

Abstract. Although there are many studies of particulate matter (PM) pollution in Beijing, the sources and processes of secondary PM species during haze periods remain unclear. Limited studies have investigated the PM formation in highly-polluted environments under low and high relative humidity (RH) conditions. Herein, we present a systematic comparison of species in submicron particles (PM1) in wintertime Beijing (29 December 2014 to 28 February 2015) for clean periods and pollution periods under low and high RH conditions. PM1 species were measured with an aerosol chemical species monitor (ACSM) and an aethalometer. Sources and processes for organic aerosol (OA) were resolved by positive…