The formation of ozone and peroxyacetyl nitrate (PAN) in the urban atmospheres of Alberta

Abstract

Atmospheric temperature inversions frequently trap pollutants in the urban atmospheres of Alberta leading to photochemical air pollution. Peroxyacetyl nitrate (PAN) was monitored, for the first time in Alberta, from November 1980 to August 1981 at the University of Calgary using electron capture gas chromatography. Measurements were made at one-half-hour intervals from July, 1981 to February, 1982 at a downtown location. Maximum PAN concentrations were recorded at the University and downtown sites on August 14 at 1400 h, 1981 and the values were 2.4 and 6.6 ppb, respectively. In each case the maximum PAN peak coincided with the afternoon peak in ozone concentrations, 79 ppb at the University and 59 ppb at the downtown site. Surprisingly, a high value of 2.3 ppb PAN was recorded at the University during January of 1981 giving rise to questions regarding the influence of low temperatures and solar radiation on the photochemical formation of PAN. Calculations employing a simple photochemical model for PAN and ozone formation have been carried out and comparisons made between the observed and the computed values.