A method for using stationary networks to observe long-term trends of on-road emission factors of primary aerosol from heavy-duty vehicles

Abstract

Abstract. Heavy-duty vehicles (HDVs) contribute a significant, but decreasing, fraction of primary aerosol emissions in urban areas. Previous studies have shown spatial heterogeneity in compliance with regulations. Consequently, location-specific emission factors are necessary to describe primary particulate matter (PM) emissions by HDVs. Using near-road observations from the Bay Area Air Quality Management District (BAAQMD) network over the 2009–2020 period in combination with Caltrans measurements of vehicle number and type, we determine primary PM2.5 emission factors from HDVs on highways in the San Francisco Bay area. We demonstrate that HDV primary aerosol emission factors derived using this method are in line with observations by other studies, that they decreased a by a factor of ∼ 9 in the past decade, and that emissions at some sites remain higher than would be expected if all HDVs were in compliance with California HDV regulations.