Measurement of ambient aerosols by single particle mass spectrometry in the Yangtze River Delta, China: Seasonal variations, mixing state and meteorological effects

Abstract Continuous measurements of ambient aerosols were performed with a single-particle aerosol mass spectrometer in Nanjing during all four seasons of 2015. Ambient particles were clustered into 11 classes, which included elemental carbon (EC) mainly with sulfate (EC-S); EC with nitrate and sulfate (EC-SN); EC with obvious organic signals (ECOC); organic carbon (OC); biomass/biofuel burning particles (Biomass); Ammonium; particles with obvious Na, K (NaK) and sulfate (NaK-S), NaK with nitrate and sulfate (NaK-SN); iron-containing particles (Fe-rich); miscellaneous metal-containing particles (MiscsMetals) and Dust. Seasonal local sources, dominated air masses and distinct atmospheric processes all affected the concentrations of various particles and caused different diurnal changes. EC-SN during summer slowly increased in the afternoon and NaK-SN had a peak at noon during winter. Differences in size distribution of each particle type between seasons were discussed. All types of particles showed unimodal number size distributions, their peak radius ranked as follows: fall  20%) as a result from the decrease in temperature and increase in relative humidity (RH). The distributions of ECOC varied with seasons and were obviously influenced by EC and OC particles. Mixing states showed seasonal variations. In general, the fractions of particles mixed with secondary species were the highest/lowest in winter/fall. The effects of meteorological conditions on particles were investigated. With the increase of RH, the fractions of EC increased, and most particles mixed with more NH 4 + and less C 2 H 3 O + . Characteristics of precipitation, such as duration and total rainfall amount, influenced particles. Enhanced secondary organic/inorganic species were found in particles during long-/short-term precipitation with intensities 4 + , C 2 H 3 O + and HSO 4 − were found during precipitation compared with non-precipitation days.