Aircraft And Ground-based Measurements Of Aerosol Physical Properties Over Shanxi Area In China

Aircraft and ground-based measurements of aerosol properties including number size distribution, optical and activation properties of aerosol particles were made in summertime over Shanxi area, China, in 2013 and 2014. Through analyzing the data obtained from the two years of observation, a comprehensive understanding and lots of parameters of aerosol particles in the lower troposphere (below 5000m) of Shanxi area were obtained. The results of this study can provide valuable experimental database and parameters for regional weather and environmental forecasting, climate prediction, and numerical simulation of aerosol, clouds and climate. The main conclusions are drawn as follows:(1) Aircraft measurements of aerosol particles (0.01～20μm) and cloud condensation nuclei (CCN) were made in the summer of 2013. Vertical profiles of particle number concentration, effective diameter (ED) and activation properties, and vertical profiles of CCN were analyzed. Fine particles with diameter smaller than 0.8μm were predominant over the region. Aerosol particle number concentration decreased exponentially with altitude, but mean particle size increased with altitude. Particle number size distributions at different height ranges showed two or three peaks. The number size distribution from 0.01μm to 20μm can be fitted with three log-normal distribution functions. The number concentration of CCN (NCCN) also decreased with altitude. Vertical profiles of CCN fraction (fCCN/CN) were similar with the vertical profiles of ED, although the fCCN/CN increased with altitude.(2) The vertical distributions of aerosol optical properties including aerosol scattering coefficients (σSC), absorption coefficients (aab), Angstrom exponent (a), the single scattering albedo (ω), back scattering ratio (βSC), aerosol mass scattering proficiency (QSC) and aerosol surface scattering proficiency (Q’SC) were measured, and both of the σSC and σab decreased with altitude. The aerosol optical properties at lower level contributed the most to the total radiative forcing. The 48h backward trajectories of air masses during the observation days indicated that the majority of aerosols in the lower level (below 2000m) were originated from local or regional pollution emissions; and aerosol particles in the upper layer (above 3000m) with lower number concentration and optical properties were transported over long distance from the north and west region of China.(3) The distribution characteristics of aerosol number spectrum, mass spectrum and aerosol scattering properties were analyzed based on the summertime ground observation experiment in Xinzhou, Shanxi Prov.,2014. The statistical average values of aerosol mass concentration, number concentration, scattering coefficient and the Angstrom index were 17.1 μgm-3,18572 cm-3,192.1 Mm-1,1.79, respectively. Daily variation of aerosol number concentration show unimodal distribution, which corresponding to the frequent new particle formation (NPF) events; daily variation of aerosol mass concentration shows bimodal characteristics, which were mainly affected by human activities; daily variation of aerosol scattering coefficient was similar with the mass concentration. Aerosol mass concentration and scattering coefficient has a good linear correlation, and the correlation coefficient is 0.95. Aerosol average number size spectrum showed two peaks, and the aerosol mass size spectrum showed unimodal feature. Aerosol particles with size less than 200nm contributed the majority of the total number concentration, and particles larger than 200nm were responsible for the main aerosol mass concentration. Potential Source Contribution Function (PSCF) analysis of possible sources of aerosol in observation area was done and the results showed that the potential sources of aerosol particles were mainly from the more industrialized and heavily populated cluster area such as Hebei and southwest region of Shandong, north and northeast regions of Henan, north region of Hubei, and the PSCF value was larger than 0.6.(4) Cloud condensation nuclei (CCN) were measured from January to December in Taiyuan of Shanxi. The temporal and spatial distribution properties of CCN were analyzed. The CCN number concentration (NCCN) showed obvious seasonal variation, and the average NCCN was highest in Winter and lowest in Summer. A bimodal pattern was presented in the NCCN diurnal variation, and the two peaks were corresponding to the time of intensive human activities and heavy transportation in a day. The fitted CCN spectra for various seasons were obtained using the expression N=CSK, and the fitted parameters C and K showed typical continental type. Size-resolved activation properties for 5 different supersaturation values (0.07%、0.1%、0.2%、0.4%、0.8%) were analyzed. Aerosol particles with size smaller than 20nm cannot active in any supersaturation value; activation ability of aerosol particles with size larger than 1 OOnm is much stronger, the corresponding activation ratio was larger than 80% when SS>0.2%; activation ratio was larger than 70% under all the supersaturation values with particle size larger than 200 nm. The typical diameter of 50% activation point (D50) of the 5 supersaturation values were 145,124,124,56, and 38 nm, respectively. Higher activation ratio and smaller D50 indicate that the aerosol particles contained high soluble chemical compositions in Shanxi area.