AAAR 33rd Annual Conference
October 20 - October 24, 2014
Rosen Shingle Creek
Orlando, Florida, USA
Abstract View
Linking Nitrogen Oxide Chemistry and Aerosol over the Last Decade in San Joaquin Valley, California
SALLY PUSEDE, Ronald Cohen, UC Berkeley
Abstract Number: 24 Working Group: Linking Aerosols with Public Health in a Changing World
Abstract Nitrogen oxide (NO$_x) abundances across the U.S. have fallen steadily over the last fifteen years. Patterns in anthropogenic sources result in 2-fold lower NO$_x on weekends than weekdays largely without co-occurring changes in other emissions. These trends taken together provide a near perfect NO$_x constraint on the nonlinear chemistry of ozone, on key oxidants hydroxyl (OH) and nitrate radical (NO$_3), and on secondary aerosol formation. We use this NO$_x constraint to interpret trends in wintertime PM$_(2.5) over the last decade in San Joaquin Valley, California, a location with severe aerosol pollution and where a large portion of the total aerosol mass is ammonium nitrate (NH$_4NO$_3). We combine the 15-year routine monitoring record and the air- and ground-based DISCOVER-AQ-2013 data set to quantify the impact of NO$_x emission controls on wintertime PM$_(2.5) concentrations. Nitrate ion (NO$_3$^–) is the oxidation product of NO$_2 and is formed by distinct daytime and nighttime pathways, both of which are nonlinear functions of the NO$_2 abundance. We present observationally derived decadal trends in both pathways and show that NO$_x reductions have dually worked to increase and decrease NH$_4NO$_3 production over the last 15 years. The net effect is a substantial decrease in NO$_3$^– via decreased production in the nighttime residual layer. We quantify the impact of future NO$_x controls on PM$_(2.5) exceedances.