Nitric Acid and Particulate Measurements by Transition-Flow Reactor During the Carbonaceous Species Methods Comparison Study

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Abstract
Measurements of gaseous nitric acid and fine and total particulate nitrate and sulfate were made by the transition-flow reactor (TFR) during the Carbonaceous Species Methods Comparison Study (CSMCS) at Glendora, CA, in August 1986. The TFR is a modular sampler especially suited for measuring reactive species that occur in both gas and particle phases. It consists of a tube operated in transition flow that has a short section lined with a sink for the gaseous species of interest. For gaseous nitric acid, the linear is nylon and it removes a constant 9%. Following the transition-flow tube is a filter pack containing a Teflon filter to remove particles and a nylon filter to remove the remaining gaseous nitric acid and any nitric acid liberated from the particles on the Teflon filter during sampling. In the CSMCS, a dual TFR system sampling through a cyclone, which had a cutpoint of 2 μm, one TFR was changed every 12 hours, the other was changed every 24 hours. A third TFR was also used that had an inverted funnel inlet which sampled particles up to approximately 10 (JLIII in diameter and was changed every 12 hours. Gaseous nitric acid concentrations averaged 33.2 (μg m−3 in the day and 2.81 μg m−3 at night. Fine (< 2 μm) particulate nitrate showed a strong diurnal variation with a daytime mean of 13.5 μg m−3 and a nighttime mean of 4.5 μg m−3. Coarse (2–10 μm) particulate nitrate comprised a substantial fraction of total particulate nitrate, being 37% during the day and 58% at night. Nitric acid concentration data from the TFR that had an inverted funnel inlet were statistically identical to those from the TFR with a cyclone inlet, indicating that there is no loss of nitric acid in the TFR's Teflon cyclone and that there is no contamination of the funnel-inlet TFR's nylon linear by coarse particles. There was no evidence of a sampling duration effect for nitric acid; the mean ratio of the mean concentrations of day and night TFRs to the 24-hour TFR was 0.95 ± 0.03.

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