Removal of NO_<i>x</i>and NO_<i>y</i>in Asian outflow plumes: Aircraft measurements over the western Pacific in January 2002

Abstract

The Pacific Exploration of Asian Continental Emission Phase A (PEACE‐A) aircraft measurement campaign was conducted over the western Pacific in January 2002. Correlations of carbon monoxide (CO) with carbon dioxide (CO 2 ) and back trajectories are used to identify plumes strongly affected by Asian continental emissions. ΔCO/ΔCO 2 ratios (i.e., linear regression slopes of CO‐CO 2 ) in the plumes generally fall within the variability range of the CO/CO 2 emission ratios estimated from an emission inventory for east Asia, demonstrating the consistency between the aircraft measurements and the emission characterization. Removal rates of reactive nitrogen (NO x and NO y ) for the study region (altitude &lt;4 km, 124°–140°E, 25°–45°N) are estimated using the correlation with CO 2 , the photochemical age of the plumes, and the NO x /CO 2 emission ratio derived from the emission inventory. The plume age is estimated from the rates of hydrocarbon decay and hydroxyl radical (OH) concentration calculated using a constrained photochemical box model. The average lifetime of NO x is estimated to be 1.2 ± 0.4 days. Possible processes controlling the NO x lifetime are discussed in conjunction with results from earlier studies. The average lifetime of NO y is estimated to be 1.7 ± 0.5 days, which is comparable to the NO y lifetime of 1.7–1.8 days that has been previously reported for outflow from the United States. This similarity suggests the importance of chemical processing near the source regions in determining the NO y abundance.