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 NO x 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-1propanol, 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 CdC functionality, such as the isoprene nitrates, reaction with OH is expected to be more important than wet deposition.

Observations of HNO<sub>3</sub>, ΣAN, ΣPN and NO<sub>2</sub> fluxes: evidence for rapid HO<sub>x</sub> chemistry within a pine forest canopy

“…ANs are a mixture of a wide range of compounds (O'Brien et al, 1995;Kastler et al, 2000;Day et al, 2003;Rosen et al, 2004;Cleary et al, 2005), many of which are hydroxyalkyl nitrates that are expected to have high deposition velocities because the hydroxyl group enhances their solubility in water (Shepson et al, 1996;Treves and Rudich, 2003). Peroxyacetyl nitrate (PAN) deposition has been observed over various grassland and forest ecosystems (Shepson et al, 1992;Schrimpf et al, 1996;Turnipseed et al, 2006), though upward PAN fluxes have been observed on hot days in the presence of precursors (Doskey et al, 2004). Upward NO 2 fluxes have been observed previously, and are attributed to NO reactions with O 3 and decreases in the NO 2 photolysis rate within forest canopies relative to above them (Gao et al, 1993;Horii et al, 2004).…”

A product study of the isoprene+NO<sub>3</sub> reaction

“…If INs maintain their nitrate functionality through an additional oxidation step, the resulting compounds would be small keto-and hydroxy-nitrates and di-nitrates which could allow for transport of oxidized nitrogen on local, regional and global scales. However these highly polar, multifunctional product nitrates may also be likely to deposit via wet or dry deposition (Shepson et al, 1996). If, on the other hand, subsequent oxidation leads to the release of NO 2 , then INs would constitute only a temporary NO x reservoir.…”

Extending the Community Multiscale Air Quality (CMAQ) modeling system to hemispheric scales: overview of process considerations and initial applications

“…In previous CMAQ versions, the Henry's law constant for peroxyacetyl nitrate (PAN) was also used for NTR, resulting in its very slow removal either through scavenging by clouds or through dry deposition at the Earth's surface. However, the Henry's law constants for several alkyl nitrates and hydroxyalkyl nitrates have been suggested to be much higher (some comparable to HNO 3 ), especially those that are of biogenic origin (Shepson et al, 1996;Treves and Rudich, 2003). On the hemispheric scale, organic nitrates formed from isoprene are the largest contributor to the simulated tropospheric NTR burden and can consequently modulate the simulated tropospheric O 3 burden.…”