Airborne Characterization of Black Carbon Aerosol in California from Biomass Burning

During the summer of 2018, the Clemson Air Quality Lab participated in the marine aerosol cloud and wildfire study (MACAWS), an aircraft-based field campaign in Monterey, CA. During this campaign, data was collected on atmospheric black carbon aerosol (BC) near the central coast of California. BC was evaluated from sources dominated by urban emissions, wildfires, and the offshore shipping industry. Data was collected on BC mass concentrations and size distribution using a single particle soot photometer (SP2). Additionally, an aerosol mass spectrometer (AMS) collected data on chemical composition of aerosols. The hypothesis being tested was as follows: different sources of air pollution generate aerosol containing unique physical and chemical characteristics. Wildfires emit different characteristic black carbon aerosol size distributions and overall chemical compositions than other sources. These characteristics can be used to search for traces of biomass burning even within polluted air masses. The purpose of this work is to increase overall understanding of ultrafine emissions from wildfires, especially black carbon particles. In order to test the hypothesis and contribute to this topic broader topic of wildfire air quality, the specific objectives are: Determine background mass concentrations of black carbon and other non-refractory species in the Sacramento Valley during fire season Investigate the size distribution of black carbon aerosol from wildfires Examine the emission of co-emitted aerosol from wildfires To use models and on board instruments to examine the plume dynamics in the atmosphere The majority of the analysis has focused on measurements of two wildfires in the Sacramento Valley (SV). The first fire, the Pawnee Fire, did not produce enough emissions to generate widespread air quality effects. Instead, it represents a background aerosol concentration for fire season in the SV. The County Fire was the most prominent event during the campaign, burning 90,000 acres in early July, 2018. The direct plume contained an over 100 times more BC than background samples. This BC had a larger size distribution, consistent with those listed in literature from wildfires. In addition to measuring the influence of the County Fire, several methods have been developed for estimating impact of future fires. One such technique used published emission factors (EF) to estimate various other chemical constituents emitted from a fire given a measured concentration of black carbon. When this technique was performed for the County Fire, emissions were estimated within a factor of 2 of measured values. Additionally, HYSPLIT models simulated the plume transportation from the fire location and were compared to the plume as described by the in-flight measurements. The work performed herein validates the background air pollution data of prior sampling campaigns in the SV and displays a complete BC size distribution for an active wildfire. Additionally, new techniques are developed that allow scientists to estimate concentration of co-emitted aerosol from fires. Atmospheric dispersion models have also been performed and compared to in flight measurements, giving policy makers additional confidence in the accuracy of a key tool in environmental public health