The Light Absorption Enhancement Characteristics Of Black Carbon Aerosols In Urban Guangzhou

Black carbon aerosol?BC?,as the main light-absorbing component of aerosol,can directly absorb solar short-wave radiation and heat the atmosphere.According to the IPCC 2013 report,black carbon is the third factor that affects climate warming.Black carbon will continue to age in the atmosphere.It is generally divided into two stages.The first stage is composed of a chain structure that is closely spherical,and the second stage It will wrap organic and inorganic shells on the spherical outer surface to produce a lens effect,enhance the absorption of black carbon,and have a major impact on climate change and the environment.However,there is still a large uncertainty in the estimation of the contribution of black carbon radiation.An important reason is that the observation of enhanced absorption of light due to the aging of black carbon particles is limited,and the previous traditional observation methods have limitations and cannot achieve long-term observations.Or,long-term observation can be achieved but the time resolution is not high,resulting in limitations in its cognition.This study applied the minimum correlation coefficient method?MRS?,using elemental carbon?EC?as a tracer to obtain the mass absorption efficiency?MAE_p?of the primary emission,combined with an aethalometer?AE33?and a carbon analyzer?ECOC analyzer?for mass absorption efficiency?MAE_t?determination.The black carbon absorption enhancement(E_abs520)can be obtained from the ratio of MAE_t/MAE_p.The atmospheric super site of Jinan University in Guangzhou City was used for sampling.The sampling campaign contain 4 periods from July 2017to March 2019,which can be divided into two dry seasons and two wet seasons:dry season 1?201711 15th-January 5,2018?and dry season 2?January 26,2019-March 31,2019?and wet season 1?July31,2017-September 10,2017?and Wet season 2?May 1,2018-July 31,2018?,the months of the four dry and wet seasons are not the same,resulting in slightly different results.The total time period covers almost 12 different months,leading to a representative dataset.Based on the data from these periods,the black carbon aerosol and its optical characteristics in the urban area of Guangzhou were analyzed.The average concentration of EC in two dry seasons(2.37±1.7?g C m^-3)was higher than the average concentration of two wet seasons(1.69±0.84?g C m^-3),the average concentration of OC in the two dry seasons(6.25±4.56?g C m^-3)is also higher than the average concentration in the wet season(3.53±2.04?g C m^-3).The primary mass absorption efficiency?MAE_p?of the black carbon 520 band showed strong seasonal changes,dry season 1:(8.6m²g^-1),wet season 1:(16.6m²g^-1),dry season 2:(26.9 m²g^-1)2.Wet season 2:(19.5 m²g^-1),E_abs520 is higher than dry season in both wet seasons,dry season 1:?1.28±0.2?,wet season 1:?1.50±0.49?,dry season 2:?1.26±0.34?,wet season 2:?1.63±0.55?,absorption angstrom exponent(AAE_470-660)is higher in the dry season than the wet season,dry season 1:?1.43±0.12?,wet season 1:?1.34±0.05?,dry Season 2:?1.39±0.12?,wet season 2:?1.31±0.08?.These results indicate that the biomass burning?BB?in the dry season affects the optical properties of black carbon.The analysis found that the aerosol loading compensation parameter k₃ value has a good correlation with the diurnal variation of AAE_470-660and E_abs520in the wet season,but there is no obvious correlation in the dry season.which may be related to the impact of BB.The influence of O₃ and NO₂,and SOC/OC on E_abs520 are discussed.The influence of SOC/OC on E_abs520 shows that the secondary process has a certain impact on E_abs520.The correlation between SOC/OC and E_abs520 is higher in the dry season than in the wet season.E_abs520 exhibit dependence on SOC/OC in both seasons.It is found that temperature has a certain effect on E_abs520.The analysis of the wind field and backward trajectory shows that light absorption of BC was enhanced during transport of air masses.