Secondary organic aerosol production from terpene ozonolysis.: 2.: Effect of NOx concentration

We report secondary organic aerosol (SOA) yields from the ozonolysis of alpha-pinene in the presence of NO and NO2. Experimental conditions are characterized by the [VOC](0)/ [NOx](0) ratio (ppbC/ppb), which varies from similar to 1 to similar to 300. SOA yield is constant for [VOC](0)/[NOx](0) > similar to 15 and decreases dramatically (by more than a factor of 4) as [VOC](0)/[NOx](0) decreases. Aerosol production is completely suppressed in the presence of NO for [VOC](0)/[NOx](0) <= 4.5. Fourier transform IR analysis of filter samples reveals that nitrate-containing species contribute significantly to the total aerosol mass at low [VOC](0)/[NOx](0). Yield reduction is a result of the formation of a more volatile product distribution as [VOC](0)/[NOx](0) decreases; we propose that the change in the product distribution is driven by changes in the gas-phase chemistry as NOx concentration increases. We also present two-product model parameters to describe aerosol production from the alpha-pinene/O-3/NOx system under both high- and low-NOx conditions.