Source Apportionment of Carbonaceous Aerosols during PM_2.5 Pollution Episodes in Xi’an, Northwestern China: Estimation of the Potential of Carbon Emission Reduction by Rural Household Energy Substitution

The carbonaceous aerosol source apportionment is crucial for targeted prevention and control of PM_2.5 in China. The 24 h integrated PM_2.5 samples were collected from Xi’an, China during pollution events in 2015 in summer (biomass open burning period) and winter (haze period). Source apportionment of carbonaceous aerosols in PM_2.5 was conducted using radiocarbon (¹⁴C) and levoglucosan (a biomass combustion tracer). Results showed that in the study period of biomass open burning in the wheat harvest season (early June) in Xi’an, fossil and non-fossil sources contributed approximately 47% and 53% to total carbon (TC), respectively. In the haze pollution period, non-fossil sources dominated water-insoluble organic carbon (WISOC) at around 53%, and fossil sources accounted for about 71% of elemental carbon (EC), with the rest from biomass combustion. The usage of coal and biomass for heating in the study period in winter increased the contribution of fossil fuel combustion to carbonaceous aerosols, particularly EC. In order to reduce PM_2.5 and carbon emission in Xi’an, controlling biomass fuels burning in summer and solid fuels use in winter are essential. Biomass fuel is a renewable negative carbon fuel, contributing significantly to greenhouse gas emission reduction. After estimation, biomass fuel usage by rural residents in Xi’an in 2015 reduced by 545,000 t of CO₂ equivalent emission, with a carbon benefit of 38.1 million yuan. Replacing scattered coal with biomass fuel could further reduce 75,500 t of CO₂ equivalent emission, generating a carbon gain of 5.29 million yuan.