The behavior of some organic nitrates at Boulder and Niwot Ridge, Colorado

Abstract

Observations show that the ratio of peroxypropionyl nitrate (PPN) to peroxyacetyl nitrate (PAN) increases to a maximum in the afternoon period at Boulder and at Niwot Ridge. In Boulder air and in easterly flow reaching Niwot Ridge, maximum average PPN/PAN ratios were near 15%, while in westerly flow or more remote continental air, the ratio was much smaller and averaged 4%. Relative to the PAN‐mixing ratios, methyl nitrate (MN) was less than 0.2% in the afternoon and less than 0.9% at night in Boulder air masses. The sum of ambient n‐propyl nitrate (NPN) and 2‐butyl nitrate (2BN) mixing ratios was also small, the diurnal average at Niwot Ridge being about 2% of the PAN‐mixing ratio. The diurnal average contribution of MN + PPN + (NPN+2BN) to the total odd nitrogen budget at Niwot Ridge was at most 4%, leaving a 21–27% shortfall between the sum of individual measurements of odd nitrogen species and the total odd nitrogen (NO y ) measurement.