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

Measurements of NOy, NOx, PAN, PPN, MPAN, C-3-C-5 alkyl nitrates, total iso prene nitrates, HNO3, HONO, and aerosol NO3- and NO2- were made during the summer 1998 intensive of the Program for Research on Oxidants: Photochemist ry, Emissions, and Transport (PROPHET). Mixing ratios of NOy, NOx, PAN, PPN , and alkyl nitrates were observed to have a strong dependence on the direc tion of transport to the site as was expected from the distribution of majo r urban and industrial sources. A. peak in NOx and NOx/NOy during the morni ng in southerly flow provides evidence for the transport of relatively unpr ocessed emissions in layers above the nocturnal boundary layer. The differe nce in PAN and PPN levels between north and south flow directions indicates a net transport of reactive nitrogen to regions farther north. Isoprene ni trates 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 deposit ion, their role in the processing of NOy may be significant. General agreem ent was observed between NOy and the sum of the individually measured const ituents during ten 24 hour periods, although a linear regression indicates the potential for an interference in the individual measurements and a poss ible shortfall in NOy. Measurements indicate that HONO may play a larger ro le in the reactive nitrogen budget than previously expected for a rural sit e. 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 pathway s.