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Direct Measurements of Secondary Organic Aerosol (SOA) Response to NOx and VOC Perturbations in the Ambient Atmosphere
SHENGLUN WU, Christopher Cappa, Qi Zhang, Benjamin Schulze, John Seinfeld, Michael Kleeman, University of California, Davis
Abstract Number: 235
Working Group: Urban Aerosols
Abstract
Secondary organic aerosol (SOA) is the dominant component of organic aerosol that significantly impacts climate change and human health. Complex components and formation mechanisms make it difficult to predict SOA response to emissions perturbations. Volatile organic carbon (VOC) compounds are the major precursor for SOA, but complex interactions with oxides of nitrogen (NOx) can impact the SOA formation in different ways. Furthermore, O3 formation that depends on NOx/VOC will also affect SOA formation. Here we directly investigate the SOA formation in the ambient atmosphere under changing NOx/VOC conditions. The sensitivity of SOA to NOx and VOC perturbations was directly measured using a mobile trailer equipped with three identical Teflon smog chambers (each 1 m3) filled with ambient air. One chamber was used as the basecase measurement, one chamber had NOx added, and one chamber had a surrogate VOC added (ethylene, m-xylene, n-hexane). A High-resolution time-of-flight aerosol mass spectrometer and scanning mobility particle sizer was installed to measure the organic aerosol in the chambers. O3, NOx, temperature, and relative humidity were also measured. Two weeks of measurements in Sacramento in April 2020 shows that both NOx and VOC perturbation suppress the SOA formation relative to the basecase conditions. The perturbed SOA formation appears to respond to both oxidant levels and to the SOA formation potential of the parent VOCs. However, the O:C ratio has an inverse response to total SOA perturbation response, suggesting more complex chemical reactions are active. These results indicate that the NOx and VOC have a large impact on SOA formation and they provide insight into how SOA formation in the ambient atmosphere will change with current emission control strategies.