Observations of reactive oxidized nitrogen and speciation of NOy during the PROPHET summer 1998 intensive

Abstract

Measurements of NOy, NOx, PAN, PPN, MPAN, C3-C5 alkyl nitrates, total isoprene nitrates, HNO3, HONO, and aerosol NO3- and NO2- were made during the summer 1998 intensive of the Program for Research on Oxidants: Photochemistry, Emissions, and Transport (PROPHET). Mixing ratios of NOy, NOx, PAN, PPN, and alkyl nitrates were observed to have a strong dependence on the direction of transport to the site as was expected from the distribution of major urban and industrial sources. A peak in NOx and NOx/NOy during the morning in southerly flow provides evidence for the transport of relatively unprocessed emissions in layers above the nocturnal boundary layer. The difference in PAN and PPN levels between north and south flow directions indicates a net transport of reactive nitrogen to regions farther north. Isoprene nitrates were observed to typically comprise less than 1% of NOy in spite of the dominance of isoprene in local VOC chemistry, although due to the rapid losses of isoprene nitrates through reaction, vertical mixing, and deposition, their role in the processing of NOy may be significant. General agreement was observed between NOy and the sum of the individually measured constituents during ten 24 hour periods, although a linear regression indicates the potential for an interference in the individual measurements and a possible shortfall in NOy. Measurements indicate that HONO may play a larger role in the reactive nitrogen budget than previously expected for a rural site. HONO/NO2 for a 24 hour period was observed to be 0.09-0.25 and suggests the likelihood of a significant heterogeneous production pathway or pathways. Copyright 2001 by the American Geophysical Union.