We present our measurements and analyses of sub-micron particulate matter (PM1) chemical composition during a highly polluted period from September 25 to 27, 2013 during the DISCOVER-AQ field campaign near Houston, TX. This episode was characterized by ozone (O3) mixing ratios in excess of 100 parts per billion and by persistence of O3 in the nocturnal boundary layer. During this period, we made measurements of PM1 with an Aerodyne High Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS) in the vicinity of Conroe, TX, which lies to the northwest of Houston and is likely to be influenced strongly by outflow from the urban core. Our findings indicate that organic nitrates from nitrate-radical-initiated reactions are an important component of PM1 in the aged outflow of the Houston, TX metropolitan area. The composition of PM1 was dominated by organics accounting for 76.4% of the mass, sulfate was the next largest component with 14.2% of the mass followed by nitrate, ammonium, and chloride which were 4.7, 4.5, and 0.2% respectively. We estimate that organic nitrates comprise approximately 25% of the measured nighttime aerosol mass for PM1 during this episode. Nighttime production of secondary organic aerosol during this period resulted in an average diurnal maximum of 15.5 �g m-3. These findings have important implications for air quality managers, as O3 and nitrogen oxides can be tied directly to increased PM1 levels at night.

Nighttime production of organic nitrate aerosol by nitrate-radical initiated reactions near Houston, TX

248th National Meeting (2014)

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