Abstract. To grasp the key factors affecting particle mass
scattering efficiency (MSE), particle mass and number size distribution,
PM2.5 and PM10 and their major chemical compositions, and the particle
scattering coefficient (bsp) under dry conditions were measured at an
urban site in Guangzhou, southern China, during 2015–2016. On an annual average,
10±2 %, 48±7 % and 42±8 % of PM10 mass were
in the condensation, droplet and coarse modes, respectively, with mass mean
aerodynamic diameters (MMADs) of 0.78±0.07 in the droplet mode and
4.57±0.42 µm in the coarse mode. 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, (NH4)2SO4, NH4NO3, and crustal element oxides in the droplet mode, and crustal element oxides, OM, and CaSO4 in the coarse mode, were the dominant chemical species in their respective modes. The measured bsp can be reconstructed to the
level of 91±10 % using Mie theory with input of the estimated
chemically resolved number concentrations of NaCl, NaNO3,
Na2SO4, NH4NO3, (NH4)2SO4,
K2SO4, CaSO4, Ca(NO3)2, OM, EC, crustal element
oxides and unidentified fraction. MSEs of particle and individual chemical
species were underestimated by less than 13 % in any season based on the estimated bsp and chemical species mass concentrations. Seasonal
average MSEs varied in the range of 3.5±0.1 to 3.9±0.2 m2 g−1 for fine particles (aerodynamic diameter smaller than 2.1 µm),
which was mainly caused by seasonal variations in the mass fractions and
MSEs of the dominant chemical species (OM, NH4NO3,
(NH4)2SO4) in the droplet mode. MSEs of the dominant chemical
species were determined by their lognormal size-distribution parameters,
including MMADs and standard deviation (σ) in the droplet mode.
Supplementary material to "Impact of particle number and mass size distributions of major chemical components on particle mass scattering efficiency in urban Guangzhou of South China"