Ammonia emissions, concentrations and implications for particulate matter formation in Houston, TX

Seasonal average observational data, photochemical modeling analyses, and detailed observational data for a summer air pollution episode were used to assess the spatial and temporal distribution of ammonia-rich and ammonia poor conditions in southeast Texas. Seasonal average observational data and photochemical modeling analyses both suggest ammonia rich conditions throughout southeast Texas, but not enough ammonia present to create elevated concentrations of ammonium nitrate, except during morning hours. Analyses of ambient data available for the summer air pollution episode (which was also the modeled episode) indicate that ammonia-poor conditions may be more pervasive in southeast Texas during periods of intense photochemistry. Overall, the results of all three methods are consistent in suggesting that average ammonia availability in southeast Texas is comparable to the ammonia required to neutralize sulfate. Temporal and spatial variability in sulfate formation creates morning excesses of ammonia (leading to some morning nitrate formation) and ammonia poor conditions in SO2 plumes and during periods of high photochemical activity.