AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Direct Measurements of Ozone Sensitivity to NOx and VOC Controls in Los Angeles
Toshihiro Kuwayama, Peter Green, Christopher Cappa, Anthony Wexler, MICHAEL KLEEMAN, University of California, Davis
Abstract Number: 443 Working Group: Urban Aerosols
Abstract Modeling studies suggest that NOx emissions controls provide an efficient method to reduce surface ozone concentrations in Los Angeles, California. Here we demonstrate a technique to directly measure ozone sensitivity to NOx or VOC changes in the ambient atmosphere as an independent check of those predictions. Three identical 1 m3 FEP bags (smog chambers) were placed in a mobile trailer. Automated pumps and valves were configured to fill each chamber with ambient air, and then to additionally perturb the chambers with: (1) NOx addition, (2) VOC addition, and (3) no change (baseline). Chambers were then exposed to UV radiation representative of summer conditions in California over a time period of 3 hrs while ozone and NOx concentrations were measured.
Results from the direct measurements of ozone sensitivity are reported from a field campaign at three locations in southern California during the summer/fall of 2014. Data was collected at each site over a time period that included both weekdays and weekends to determine how changing emissions altered the optimum ozone control strategy. The measurements in Los Angeles indicate that the baseline chamber followed the ambient concentrations reasonably well over the 3 hr experiment. NOx and VOC perturbations produced changes in ozone formation rates that could be detected with +90% statistical certainty relative to the baseline behavior. 11 out of 13 weekday measurements indicated that the atmosphere had excess NOx (small NOx increase gave lower O3). 5 out of 6 weekend measurements indicated that the atmosphere had limited NOx (small NOx increase gave greater O3). 19 out of 19 measurements indicated that increasing VOC will increase O3. Taken together, these findings suggest that optimized future emissions control programs for ozone reduction in LA should include some amount of VOC control in addition to NOx control.