Deriving Fleet-wide Emissions Factors of Aerosol from Dense, Stationary Networks

On-road mobile sources contribute a significant fraction of primary aerosol emissions in urban areas. Current emissions estimates are based on modeled emissions factors which take into account make and age of vehicles in a modeled fleet, but which may not account for vehicle maintenance, driving conditions, or compliance rates for control technologies. For example, in the past 10 years, control technologies such as the diesel particulate filters have greatly reduced particulate emissions from compliant heavy duty trucks. However, multiple studies quantifying emissions factors from single vehicle plumes have shown that while compliance is high at regulated sites such as ports, the fraction of out of compliance vehicles may be significantly higher in other locations. Additionally, prior on-road studies show that aerosol emissions factors of both passenger vehicles and heavy duty trucks vary by at least an order of magnitude within the middle two quartiles. To gain a better estimate of total emissions of primary aerosol by on-road vehicles, we quantify on-road, fleet-wide emissions factors of PM_2.5 in the San Francisco Bay Area. We do this by leveraging the spatial and temporal coverage of two networks: The Berkeley Environmental Air Quality CO₂ Observation Network (BEACO₂N), a dense (2km spacing) network of low-cost sensors measuring aerosol, CO₂, CO, and other trace gases, and the Bay Area Air Quality Management District Network (BAAQMD) which consists of sites which measure both aerosol and CO, some of which have been in operation for more than a decade.