SIMULTANEOUS CONCENTRATIONS OF AMMONIA AND NITRIC-ACID IN A POLLUTED ATMOSPHERE AND THEIR EQUILIBRIUM RELATIONSHIP TO PARTICULATE AMMONIUM-NITRATE

Simultaneous absolute concentrations of NH3 and HNO3 in ambient air were measured with short integration times (<6 min) in Riverside, Calif., in 1977 using a kilometer path-length Fourier transform infrared (FT-IR) spectrometer. From 249 spectra, 54 cases were found where the concentrations of both NH3 and HNO3 were above the detection limits of 4 and 6 ppb, respectively. During selected episodes, 24-h high-volume particulate samples were also collected on washed Gelman AE glass fiber filters and analyzed for ammonium and nitrate ions. Analysis of these data supports the hypothesis that particulate ammonium nitrate is in equilibrium with its precursors, NH3 and HNO3, and suggests that the ammonium nitrate equilibrium constant derived from published thermochemical data gives a reasonable upper limit for the concentration product of gas-phase NH3 and HNO3 in the atmosphere. © 1979, American Chemical Society. All rights reserved.