Seasonal and shorter-term variations in particulate atmospheric nitrate in Baltimore (original) (raw)

Fine particle nitrate concentrations were measured at 10-min intervals for approximately 9.5 months beginning on 14 February 2002, at the Baltimore Supersite Ponca St. location using an R&P 8400N semi-continuous monitor. The measurement results were used to characterize seasonal and shorter-term excursions in nitrate concentrations and determine their influence on PM 2.5 concentrations. Over the 9.5-month study period, nitrate levels of 1.771.6 mg m À3 accounted for 11.4% of the PM 2.5 mass. Monthly averages ranged from 0.8 mg m À3 in August to 2.9 mg m À3 in November, and accounted for 4.7-17.3% of monthly PM 2.5 mass. Hourly averages, however, were often larger, especially in the colder months, owing to numerous relatively short-term transients, where hourly nitrate concentrations exceeded 5.0 mg m À3 . These often occurred along with NO x and ultrafine particle transients during the morning commute hours.