A Black Carbon-Tracer Method for Estimating Cooking Organic Aerosol From Aerosol Mass Spectrometer Measurements

Cooking organic aerosol (COA) constitutes a considerable fraction of organic aerosol (OA) in urban environments, yet it is often challenging to resolve COA in summer through positive matrix factorization of unit mass resolution spectra of OA from aerosol mass spectrometer measurements. Here we developed a black carbon-tracer method for estimating COA in summer. The estimated COA agreed reasonably well with those from other methods. This method can also be applied to other seasons and megacities without substantial emissions from biomass burning and coal combustion. Globally, much higher COA concentrations in China and India than those in North America and Europe were observed, while the COA contributions were comparable (15.5-20%), highlighting the importance of COA in urban areas. Considering the rapidly increased aerosol mass spectrometer measurements worldwide, this method has significant implications for a better source apportionment of OA and also benefits the health studies associated with cooking exposure. Plain Language Summary Cooking is one of the most important primary sources in urban environments and may have a significant impact on premature mortality in densely populated areas. While aerosol mass spectrometer is capable of measuring cooking organic aerosol (COA) in real time, it is often challenging to separate it from traffic-related primary emissions, especially in summer. Here we found that black carbon is a good tracer to separate traffic and COA in the absence of biomass burning and coal combustion emissions. The successful applications of the black carbon-tracer method to Beijing and Nanjing for COA estimates highlight its wide implications for better source apportionment of organic aerosol and future exposure studies in urban areas.