Impact of particle number and mass size distributions of major chemical components on particle mass scattering efficiency in urban Guangzhou of South China (original) (raw)

Atmospheric Chemistry and Physics Discussions

To grasp the key factors affecting particle mass scattering efficiency (MSE), particle mass and number size distribution, bulk PM 2.5 and PM 10 and their major chemical compositions, and particle scattering coefficient (b sp) under dry condition were measured at an urban site in Guangzhou, south China during 2015-2016. On annual average, 10±2%, 48±7% and 42±8% of PM 10 mass were in the condensation, droplet and coarse modes, with mass median aerodynamic diameters (MMADs) of 0.21±0.00, 0.78±0.07 and 4.57±0.42 µm, respectively. The identified chemical species mass concentrations can explain 79±3%, 82±6% and 57±6% of the total particle mass in the condensation, droplet and coarse mode, respectively. Organic matter (OM) and elemental carbon (EC) in the condensation mode, OM, (NH 4) 2 SO 4 , NH 4 NO 3 and crustal element oxides in the droplet mode, and crustal element oxides, OM and CaSO 4 in the coarse mode were the dominant chemical species in their respective modes. The measured b sp can be reconstructed to the level of 91±10% using Mie theory with input of the estimated chemically-resolved number concentrations of NaCl, NaNO 3 , Na 2 SO 4 , NH 4 NO 3 , (NH 4) 2 SO 4 , K 2 SO 4 , CaSO 4 , Ca(NO 3) 2 , OM, EC, crustal element oxides and unidentified fraction. MSEs of bulk particle and individual chemical species were underestimated by less than 13 % in any season based on the estimated b sp and chemical species mass concentrations. Seasonal average MSEs varied in a small range of 3.5±0.1 to 3.9±0.2 m 2 g-1 for fine particles, which was mainly caused by seasonal variations of the mass fractions and MSEs of OM in the droplet mode.