Characteristics Of Black Carbon Aerosol And Its Influencing Factors In Typical Cites Of The PRD

Black carbon aerosol（BC）not only causes deterioration of air quality,but also has an important influence on climate change and public health.The observation and research of BC has substantial academic value and practical application demand in the field of environment,climate and human health.In this study,two models of Aethalometer are used to measure the concentration of BC in the typical city of Pearl River Delta（PRD）,Guangzhou（AE-33）and Shenzhen（AE-31）.Combined with the meteorological data of all sites,the BC pollution characteristics of different representative sites in the PRD in different time periods were analyzed.In this study,AAE values of different sites were also calculated to estimate the possible sources of local BC.The influence of pollutant on BC concentration in different direction was analyzed by combining the backward trajectory model and the near-surface wind field data.Relevant results are of great significance for understanding the status and cause of air pollution in the PRD region.Observation sites of this study are:XC（suburban site）and ZZL（urban site）in Shenzhen,JNU（urban site）in Guangzhou.The observation period of XC and ZZL sites in Shenzhen is from January 1,2014 to June 30,2015,and the observation period of JNU site in Guangzhou is from October 1,2015 to May 31,2016.The major findings are listed as follows:1、During the campaign,the BC average concentrations at XC、ZZL and JNU sites were（1.12±0.90）μg·m^-3,（2.58±2.00）μg·m^-3 and（2.91±2.28）μg·m^-3 respectively.The background concentrations at the three sites were（0.27±1.31）μg·m^-3,（1.07±0.85）μg·m^-3 and（1.43±0.69）μg·m^-3 respectively.The_abs at the three sites were（5.87±4.81）Mm^-1,（13.47±10.50）Mm^-1 and（22.60±17.69）Mm^-1respectively.It was found that the background concentrations of the three sites were lower than their average concentrations and that the BC concentrations at all sites were following the logarithmic normal distribution.It was found that the BC and_abs at the urban sites were much higher than those at the suburban site and the values in JNU site were higher than the ZZL site.BC concentrations were much lower at XC site than in the PRD Region.The BC concentration at XC site was close to the global background concentration（Waliguan,Qinghai）and the ocean atmosphere background concentration（Yongxing Island,Hainan）,showing that the XC site can be regarded as the regional background station in the PRD Region.2、Two distinct diurnal patterns of BC with two high peaks was observed at ZZL and JNU sites.In contrast,XC site did not show obvious diurnal variations.The time of peak and valley were consistent with the rush hours and the characteristics of atmospheric boundary layer changes.It was found that the BC concentrations at the three sites were higher in the dry season than that in the rainy season and higher in the night-time than that in the daytime.3、The Absorption Angstrom Exponent（AAE）can be considered as an indicator of BC mixing state.It was found to be close to 1 at three sites,indicating that BC at the PRD were dominated by fossil fuel combustion.Future analysis indicated that BC at XC site was mainly affected by the pollutant discharged from dock ships.While BC at ZZL and JNU sites were affected by the local automotive exhaust emissions.4、There were substantial differences between urban and suburban sites on the effect of near-surface wind field.BC at the ZZL and JNU sites were affected by the surrounding areas and local emissions.When the wind speed is low,BC is easy to accumulate,leading to the increase of BC concentration.While BC at XC site was mainly affected by the long range transport and BC concentrations at XC site were usually associated with strong northwest wind（10²0m/s）when polluted aerosols were transported from the container wharf（Shenzhen Yantian Ports）,which is the world’s third largest container terminal.5、According to the backward trajectories clusters analysis,The BC concentration in the PRD was higher when affected by the heavily polluted airmass from eastern China and coastline.While the BC concentration in the PRD was lower when affected by the airmass from the South China Sea.The pollutants emitted around the ZZL site and the local pollutants were easy to accumulate.Because of the small-scale vortex flow in the PRD,the ZZL site showed similar pollution characteristics to typical cities in the PRD.The prevailing winds in the PRD were different in dry and rainy seasons.Airflow transport from the Taiwan strait was an important factor for BC in the PRD.This study is one of the limited studies in China using the new Aethalometer（AE-33）for BC measurements.This study also gives detailed descriptions of the use and data processing of new Aethalometer（AE-33）and old Aethalometer（AE-31）.