A long-path infra-red study of Los Angeles smog

Abstract Gaseous air pollutants have been measured in Los Angeles smog by the method of long-path infra-red absorption spectroscopy. A Fourier transform spectrometer operated at 0.25cm−1 resolution was used in conjunction with a 1260-m optical path folded along a base path of 23 m. Detection sensitivities were in the parts-per-billion range. Compounds measured included NH3, CO, H2CO, HCOOH, CH3OH, HNO3, NO, NO2, O3, peroxyacetyl nitrate, alkyl nitrates and various hydrocarbons. The rise and fall of pollutant concentrations is reported in detail for the smoggy two-day period of 26 and 27 June 1980. Reactive hydrocarbons and nitrogen oxides were oxidized during the daytime, yielding ozone, aldehyde, nitric acid and peroxyacetyl nitrate. The observed gaseous reaction products only accounted for about 20 % of the nitrogen oxides that disappeared during the day. It is deduced that the “missing” 80% of the nitrogen was removed heterogeneously into aerosol particles or on surfaces at ground level.