Henry's Law Constants and Removal Processes for Several Atmospheric β-Hydroxy Alkyl Nitrates

Abstract

The oxidation of atmospheric alkenes by OH radicals results in small yields of β-hydroxy alkyl nitrates that can then provide a vehicle for the ultimate removal of NOx from the atmosphere. Although rainout may be an efficient mechanism for the removal of these species from the atmosphere, the Henry's law constants for these species are largely unknown. In this work, the Henry's law constants for β-hydroxy alkyl nitrates that are produced from the atmospheric oxidation of small alkenes in the presence of NO have been determined, over the temperature range 279−304 K. The compounds investigated were 2-nitrooxyethanol, 1-nitrooxy-2-propanol, 2-nitrooxy-1-propanol, 2-nitrooxy-3-butanol, 1-nitrooxy-2-butanol, and 2-nitrooxy-1-butanol. At 298 K, the measured Henry's law constants were 38 800, 10 900, 4500, 10 100, 5800, and 6 000 M/atm, respectively. From estimates of the rates of removal of these species from the lower troposphere by wet and dry deposition, OH radical reaction, and photolysis, we find that wet deposition accounts for between 26 and 60% of the removal rate, on average. Calculated atmospheric lifetimes for these species are all on the order of 2−3 days, which is long enough for long-range transport of these species to be possible. For hydroxy nitrates that retain a CC functionality, such as the isoprene nitrates, reaction with OH is expected to be more important than wet deposition.