Measurement report: dual-carbon isotopic characterization of carbonaceous aerosol reveals different primary and secondary sources in Beijing and Xi'an during severe haze events

摘要: Abstract. To mitigate haze pollution in China, a better understanding of the sources carbonaceous aerosols is required due to the complexity multiple emissions and atmospheric processes. Here we combined the analysis radiocarbon stable isotope 13 C investigate the formation collected two Chinese megacities (Beijing Xi'an) during severe events “red alarm” level from December 2016 January 2017. The periods with daily PM 2.5 concentrations as high ∼  400  µ g m −3 were compared subsequent clean (i.e., PM less than median winter 2016/2017) below 100  Xi'an 20  Beijing. In Xi'an, liquid fossil fuel combustion was the dominant source elemental carbon (EC; 44 %–57 %), followed by biomass burning (25 %–29 %) coal (17 %–29 %). In Beijing, contributed 45 %–61 % EC, biomass burning (17 %–24 %) (22 %–33 %) contributed less. Non-fossil 51 %–56 % organic carbon (OC) 63 %–69 % OC in Beijing. Secondary (SOC) was largely by non-fossil in Xi'an ( 56±6  %) Beijing 75±10  %), especially periods. vs. non-fossil contributions EC did not change drastically in both However, periods, contribution of increased and decreased During primary biomass burning and constituted  70 % and  53 % From the contribution SOC total but decreased in Beijing, suggesting that contribution secondary organic aerosol formation to more efficient Beijing, fraction periods was mainly an elevated SOC. a slight day–night difference observed period with enhanced contributions day. This day–night difference negligible likely enhanced accumulation pollutants under stagnant weather conditions.