VCP vs. BVOC Contributions to O3 Formation during the RECAP Field Campaign in Los Angeles, CA
Shenglun Wu, Chris Alaimo, Shang Liu, Toshihiro Kuwayama, Peter Green, Thomas Young, MICHAEL KLEEMAN,
University of California, Davis Abstract Number: 411
Working Group: Source Apportionment
AbstractOzone (O3) concentrations in Los Angeles have remained at unhealthy levels in recent years despite continued efforts to reduce precursor emissions of Volatile Organic Compounds (VOCs) and oxides of nitrogen (NOx). Significant mobile-source VOC reductions have made other residual sources (e.g., volatile chemical products (VCPs)) and biogenic VOC (BVOC) more important in urban O3 chemistry. Additional measurements are needed to identify the contribution of these VOCs to O3 formation.
Here we analyze trends in ambient NOx, O3, and VOC concentrations measured during the RECAP-CA field campaign in Redlands, CA between July and October, 2021. Atmospheric VOC samples were collected from 10AM to 12PM using Markes Universal Thermal Desorption (TD) tubes and 2,4-dinitrophenylhydrazine (DNPH) tubes. VOCs were measured in the lab by GC-MS and LC-MS following a rigorous protocol of multi-point calibrations using authentic standards. A total of 95 VOC species were found above detection limits including hydrocarbons, halogenated and oxygenated VOCs, and siloxanes.
Positive Matrix Factorization (PMF) applied to the VOC measurements identified nine VOC sources including traffic-related, biogenics, VCPs (Siloxane), plant decomposition, ethanol derived from VCPs, commercial and industrial solvents, and two local institutions related sources. O3 formation associated with PMF sources was estimated through a VOC-reactivity-based method and a method based on photochemical box model. The reactivity-based method uses Ozone Formation Potential (OFP) to calculate the fraction of the O3 formation associated with each PMF source. The box-model-based method utilized an O3 source apportionment calculation carried out under observed atmospheric conditions. The two O3 apportionment methods predicted similar VOC source contributions to O3 formation, building confidence in the results. BVOCs (~25%) made the largest contribution to O3 formation. VCPs made a lower contribution (~20%) than BVOC, and traffic-related VOCs made an even lower contribution (~15%). Implications for emissions control strategies will be discussed.