Factors Influencing The Amount Of Atmospheric Black Carbon Over The Southern Ocean And The Tropical Western Pacific Ocean

The black carbon(BC),with a total climate forcing of+1.1 W/m2,has received a lot of attention because it is the second most important anthropogenic contributor in global warming after carbon dioxide(CO2)and an ice melting enhancer that triggers a series of albedo feedback and surface temperature response leading to an amplification of warming effect in the polar and alpine regions.BC aerosol being inert has a longer residence time in the atmosphere,so can be transported over long distances.Meanwhile,the gradually increasing number of tourist visit(shipborne dominant)also contributes a share to BC abundance over the Antarctic.Therefore,local and long-range transported BC aerosols may result in perceptible impacts on the local synoptic and climatic system and vulnerable ecosystem of the Antarctic.Thus,knowing the concentration and distribution of BC aerosol in the Antarctic are of significant climatic and ecological importance.However,systematic measurements of BC over the Antarctic are very sparse.Only a few atmospheric records of black carbon exist from Antarctica,not to mention the broad circumpolar sea areas.During the 34th Chinese Antarctic Research Expedition(CHINARE)from November 8,2017 to April 20,2018,the concentrations of BC were simultaneously measured by two methods.One was in-situ observation using Multi-Angle Absorption Photometer(MAAP),which yielded equivalent black carbon(EBC),the other was to collect filter samples that were then analyzed by thermal/optical carbon analyzer,which produced elemental carbon(EC).The auxiliary data,including nitrogen oxide(NOx),were measured as well.The EBC and EC were significantly correlated,indicating both methods are appropriate to measure BC over oceans.We found that interpretation of ship-based data should be undertaken with caution,as the data derived from docking periods,low-speed sailing periods,stern wind periods and operation periods are likely affected by ship emissions.Large values of NOx concentrations combined with navigation records and air mass backward trajectory analysis can be good indicators when identifying ship emissions.After excluding the data potentially affected by ship emission,the values of EBC concentrations falling in the "0-50 ng/m3" and“?1000 ng/m3" bins showed higher proportions.Three typical periods were identified to do case studies.The factors influencing the level of EBC were investigated based upon air mass backward trajectory analysis and navigation records archived synchronously.Ship emissions,mobile and stationary emissions from Antarctic research stations may enhance EBC over the Southern Ocean,while terrestrial sources could cause increase of EBC over the tropical western Pacific Ocean.Excluding the influences of anthropogenic activities,the background EBC concentrations of the Southern Ocean,the Ross Sea and tropical ocean were 7.86±15.52 ng/m3,22.55 ± 21.53 ng/m3 and 17.80± 32.71 ng/m3,respectively,which are consistent with the EBC baseline in remote ocean(?50 ng/m3).This study,to the best of our knowledge,is the first in-situ observations of atmospheric BC over the Southern Ocean(the Ross Sea),with potential implications for simulation studies.