Emission Verification for Ozone Precursors
TRINITY OLGUIN, Gabrielle Cano, Pierre Herckes, Matthew Fraser, Arizona State University
Abstract Number: 222
Working Group: Aerosol Chemistry
Abstract
Tropospheric ozone is formed from atmospheric precursors such as NOX and volatile organic compounds (VOCs). In addition to being ozone precursors, VOCs contribute to secondary organic aerosol (SOA) formation which contributes to worsened air quality. In the Phoenix metropolitan area, which is partially in violation of the federal quality standards for ozone, VOC emissions are monitored and estimated by the Maricopa County Air Quality Department (MCAQD). In the four most recent Periodic Emissions Inventories (PEIs), it was estimated that biogenic VOC emissions exceeded anthropogenic VOC emissions. It was also estimated that these biogenic VOC emissions increased by approximately 2.4 times from 2011 to 2014, and then decreased by 2.2 times from 2017 to 2020. These changes may have been caused by updates to the model, the Model of Emissions of Gases and Aerosols in Nature (MEGAN), as well as the model’s inability to accurately estimate BVOC emissions in this southwestern desert region. The MEGAN model is more commonly informed by areas with nature profiles that are significantly different than the Sonoran Desert. Due to these large observed changes in modeled estimates, it is necessary to verify the BVOC emissions to ensure that government agencies take the most effective steps toward decreasing tropospheric ozone and SOA formation. These verifications are done using the eddy covariance technique, which correlates fast gas concentration measurements with wind measurements to calculate BVOC fluxes at an ecosystem scale. The use of a proton transfer reaction time-of-flight mass spectrometer coupled with a gas chromatograph (PTR-TOF-MS/GC) allowed for the characterization and quantification of BVOC emissions throughout different seasons. Here we present the preliminary results of the spring and summer field studies investigating BVOC fluxes in Maricopa County, Arizona.