AAAR 33rd Annual Conference
October 20 - October 24, 2014
Rosen Shingle Creek
Orlando, Florida, USA
Abstract View
Characterization of Nocturnal Aerosol Formation in Houston during DISCOVER-AQ
H. William Wallace, Yu Jun Leong, Basak Karakurt Cevik, Madeline Camp, James Flynn, Barry Lefer, ROBERT GRIFFIN, Rice University
Abstract Number: 195 Working Group: Urban Aerosols
Abstract An Aerodyne High-Resolution Time-of-Flight Aerosol Mass Spectrometer was deployed aboard a mobile laboratory during the NASA DISCOVER-AQ mission in Houston, Texas during September 2013 and during several shorter periods through late 2013 and early 2014. Additional measurements included black carbon using an aethalometer, relevant trace gases including ozone (O3), nitrogen oxides (NOx), sulfur dioxide, volatile organic compounds (VOCs), and carbon monoxide (CO), and meteorological parameters. Based on previous (2006) observations in Houston of a local nocturnal peak in the CO-scaled diurnal profile of the sampled sub-micron oxidized organic particulate matter, analysis focused on characterization of nighttime aerosol in this study. This focus also was motivated by enhanced organic aerosol loadings at night during more polluted periods within the DISCOVER-AQ timeframe. The nocturnal organic aerosol during such periods was characterized spectrally by a small relative degree of oxidation of the organic material (based on the relative contributions of the signals of mass-to-charge ratio (m/z) 44 and m/z 43). The material also displayed an enhanced ratio of the signal of m/z 30 to that of m/z 46, from which it can be inferred that the aerosol is influenced strongly by organic nitrates. Estimates indicate that organic nitrates comprised approximately 25% of the organic aerosol during periods of enhanced organic aerosol at night. Estimates of the rate of formation of nitrate radical, which is expected to be large due to the high levels of NOx and O3 in the Houston atmosphere, correlate with increases in organic aerosol loading, implying that nitrate radical oxidation of VOCs followed by phase partitioning of the resulting products is responsible for the local increases in particulate mass concentration. Analyses from measurements made near primary aerosol sources also will be highlighted.