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Particulate nitrate measurements in rural areas of the western United States
Institution:1. Department of Environmental Science, Baylor University, Waco, TX, USA;2. The Institute of Ecological, Earth, and Environmental Sciences, Baylor University, Waco, TX, USA;3. Department of Chemistry, University of Michigan, Ann Arbor, MI, USA;1. Department of Chemistry, College of Science, Al-Imam Mohammad Ibn Saud Islamic University (IMSIU), Riyadh, Saudi Arabia;2. Department of Chemistry, College of Science, Princess Nourah bint Abdul Rahman University;3. Deanship of Scientific Research, Princess Nourah bint Abdul Rahman University, Saudi Arabi;4. Department of Chemistry, College of Science, Jazan University, Jazan, Saudi Arabia
Abstract:As part of the Western Regional Air Quality Study (WRAQS), Teflon particle filters and Nylon backup filters were used to sample fine-particle nitrate and gaseous HNO3 over the course of 1 year at rural sites in nine western states. Observed nitrate concentrations were generally low in the southern part of the network, even when allowances are made for possible losses of particulate nitrate in sampling and analysis. Particulate nitrate concentrations were substantially higher in the northern portion of the network, both in absolute terms and relative to sulfate concentrations. Measured HNO3 concentrations, which were inflated over ambient levels by any volatilization of particulate nitrate during sampling, never exceeded 0.5 μg m−3 at the majority of sites. Occasional episodes of very high particulate nitrate concentrations were recorded; almost 15 % of the total particulate nitrate measured during the year was contributed by the five samples, out of the nearly 1500 analyzed, in which concentrations exceeded 1.5 μg m−3. These episodes manifested themselves not only in elevated nitrate concentrations, but in extinction coefficients and particulate mass concentrations which could not be accounted for by other measured chemical species.
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