Mobile Measurements of Carbonaceous Aerosol in Microenvironments to Discern Contributions from Traffic and Solid Fuel Burning

The relative contribution (BCsfb/BCtr ratio) of black carbon (BC) from traffic and solid fuel burning were evaluated in different microenvironments. We used a mobile platform to measure concentrations of BC and Delta-C (DC) in four microenvironments (diesel plume, urban freeway, urban street, and rural freeway). A total of 38,661 measurements of BC and DC concentrations each averaged over 5 s (in winter 2018 and fall 2020) were used to evaluate the BCsfb/BCtr ratio. Measurements were divided into three sampling campaigns (2018 nonholiday, 2020 nonholiday, and 2020 holiday) to evaluate holiday and ambient temperature impacts on the BCsfb/BCtr ratio. There was a large reduction of BC but not DC concentrations during holidays. We found elevated BCsfb/BCtr ratios in winter 2018 and fall 2020 that can be related to residential heating and cooking, respectively. A strong linear relationship (R-2 = 0.89, p < 0.05) between DC/BC ratios and BCsfb/BCtr ratios in the four microenvironments is shown as evidence that the DC/BC ratio is an indicator for solid fuel burning emissions and is independent of sampling technique and location. The relationship between DC/BC and BCsfb/BCtr ratios can be further used to quantitatively discern BC contributions from traffic and solid fuel burning emissions regardless of the type of microenvironments.