Retrieval of the Single Scattering Albedo of Asian Dust Mixed with Pollutants Using Lidar Observations

The vertical distribution of single scattering albedos （SSAs） of Asian dust mixed with pollutants was derived using the multi-wavelength Raman lidar observation system at Gwangju （35.10°N,126.53°E）.Vertical profiles of both backscatter and extinction coefficients for dust and non-dust aerosols were extracted from a mixed Asian dust plume using the depolarization ratio from lidar observations.Vertical profiles of backscatter and extinction coefficients of non-dust particles were input into an inversion algorithm to retrieve the SSAs of non-dust aerosols.Atmospheric aerosol layers at different heights had different light-absorbing characteristics.The SSAs of non-dust particles at each height varied with aerosol type,which was either urban/industrial pollutants from China transported over long distances at high altitude,or regional/local pollutants from the Korean peninsula.Taking advantage of independent profiles of SSAs of non-dust particles,vertical profiles of SSAs of Asian dust mixed with pollutants were estimated for the first time,with a new approach suggested in this study using an empirical determination of the SSA of pure dust.The SSAs of the Asian dust-pollutants mixture within the planetary boundary layer （PBL） were in the range 0.88-0.91,while the values above the PBL were in the range 0.76-0.87,with a very low mean value of 0.76 ± 0.05.The total mixed dust plume SSAs in each aerosol layer were integrated over height for comparison with results from the Aerosol Robotics Network （AERONET） measurements.Values of SSA retrieved from lidar observations of 0.92 ± 0.01 were in good agreement with the results from AERONET measurements.

Lockdown-induced Urban Aerosol Change over Changchun, China During COVID-19 Outbreak with Polarization LiDAR

Depending on various government policies,COVID-19(Corona Virus Disease-19) lockdowns have had diverse impacts on global aerosol concentrations.In 2022,Changchun a provincial capital city in Northeast China,suffered a severe COVID-19 outbreak and implemented a very strict lockdown that lasted for nearly two months.Using ground-based polarization Light Detection and Ranging(LiDAR),we detected real-time aerosol profile parameters(EC,extinction coefficient;DR,depolarization ratio;AOD,aerosol optical depth),as well as air-quality and meteorological indexes from 1 March to 30 April in 2021 and 2022 to quantify the effects of lockdown on aerosol concentrations.The period in 2022 was divided into three stages:pre-lockdown(1-10 March),strict lockdown(11 March to 10 April),and partial lockdown(11-30 April).The results showed that,during the strict lockdown period,compared with the pre-lockdown period,there were substantial reductions in aerosol parameters(EC and AOD),and this was consistent with the concentrations of the atmospheric pollutants PM_(2.5)(particulate matter with an aerodynamic diameter ≤2.5 μm) and PM_(2.5)(particulate matter with an aerodynamic diameter ≤10 μm),and the Oconcentration increased by 8.3%.During the strict lockdown,the values of EC within0-1 km and AOD decreased by 16.0% and 11.2%,respectively,as compared to the corresponding period in 2021.Lockdown reduced the conventional and organized emissions of air pollutants,and it clearly delayed the time of seasonal emissions from agricultural burning;however,it did not decrease the number of farmland fire points.Considering meteorological factors and eliminating the influence of wind-blown dust events,the results showed that reductions from conventional organized emission sources during the strict lockdown contributed to a 30% air-quality improvement and a 22% reduction in near-surface extinction(0-2 km).Aerosols produced by urban epidemic prevention and disinfection can also be identified using the EC.Regarding seasonal sources of agricultural straw burning,the concentrated burning induced by the epidemic led to the occurrence of heavy pollution from increased amounts of atmospheric aerosols,with a contribution rate of 62%.These results indicate that there is great potential to further improve air quality in the local area,and suggest that the comprehensive use of straw accompanied by reasonable planned burning is the best way to achieve this.

A method for estimating the fraction of mineral dust in particulate matter using PM2.5-to-PM10 ratios

A simple method for estimating the contributions of mineral dust to PM2.5, PM10, or TSP is presented. The method is based on the assumption of external mixing of two types of particles with different PM2.5/PM10 ratios, The method was applied to local and transported dust events observed in Tsukuba, Japan, and was compared with collocated polarization lidar measurements. The method was then applied to three dust events that occurred in Oki, Rishiri, and Ochiishi,Japan, in 2012. The results showed that the method was useful for detecting mineral dust and for qualitatively describing the mixing of dust with anthropogenic aerosols.