Concentrations and phase distributions of nitrated and oxygenated polycyclic aromatic hydrocarbons in ambient air

The concentrations of nitrated and oxygenated polycyclic aromatic hydrocarbons (PAH) in ambient air, both in the vapor phase and adsorbed on airborne particles, were measured over a 12-month period in Houston, Texas. Seasonal variations in the levels of the target compounds were weakly related to changes in ambient temperature, but more strongly related to fluctuations in the levels of ozone (O3), nitrogen dioxide (NO2), and other oxides of nitrogen (NOx). Phase distributions of the target compounds were determined by the denuder difference method. These phase distributions varied greatly over 12 months and were related to the molecular sizes, hence vapor pressures, of the compounds, but few significant associations were found between the percentages of compounds present in the vapor phase and ambient temperatures.