Diurnal Trends Differentiate Anthropogenic and Biogenic Terpenes in the Los Angeles Basin

Terpenoids play a significant role in the formation of tropospheric ozone and secondary organic aerosol. While terpenoids are largely attributed to biogenic sources, they are also widely used in consumer products that end up in the atmosphere. Terpenoid mixing ratios are reported here from samples collected during the Los Angeles (LA) Air Quality Campaign (LAAQC) in 2022 and were compared with data from three other campaigns in the LA Basin conducted between 2010 and 2021. Across all campaigns, differences in diurnal mixing ratios and composition suggest anthropogenic sources are predominant contributors to terpenoid mixing ratios in the evening to early morning (22:00–6:00 PDT), shifting to predominately biogenic sources in the afternoon (10:00–18:00 PDT). This manuscript presents the first evidence for a significant presence of anthropogenic terpenoids in the LA Basin and highlights the need for systematically studying anthropogenic and biogenic terpenoid emissions in urban areas.