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.

No abstract

Abstract. Measurements of alkyl and multifunctional organic nitrates were conducted at a rural site in Ontario during periods with varying levels of photochemical activity. On August 6 and August 21-23, 1992, a total of 17 organic nitrates (12 C3-C6 alkyl nitrates, 4 C2-C4 hydroxynitrates and 1,2-dinitrooxybutane) were quantitatively determined in atmospheric samples. The sum of the organic nitrate concentrations was found to be correlated with ozone and ranged from 12 to 140 parts per trillion (volume). The total concentration of organic nitrates measured contributed from 0.5 to 3.0% to the total odd nitrogen species. On average, the alkyl nitrates represented 82%, the hydroxynitrates 16%, and the dinitrate 2% of the total measured organic nitrates. Unidentified organic nitrate peaks determined from an organic nitrate selective detector were found to contribme an additional 0.25% to the total odd nitrogen budget. The distribution of alkyl and hydroxy nitrates measured was found to be reasonably consistent with computed relative production rates, for photochemically active air masses. Although the inclusion of the multifunctional organic nitrates does not significantly change the measured contribution of these species to NO.,, it is shown that the isoprene nitrates may ß , x y contribute as much as the combined contribution of all the measured organic nitrates.

No abstract

Particle and gas phase inorganic bromine, total organic bromine, and several individual organic bromine species were measured in the troposphere during the Polar Sunrise Experiment at Alert, Northwest Territories, Canada, during January 18 to April 21, 1992. The measurements revealed the following: (1) Particle bromide increased gradually from about 10 ng (Br) m−3 during the dark period to >20 ng(Br) m−3 during the light period, with a marked peak of 120 ng(Br) m−3 corresponding to a strong O3 depletion event. (2) Inorganic gaseous bromine (InorgBr) was about 60 ng(Br) m−3 during the dark period and relatively constant. A major peak, up to 280 ng(Br) m−3, before sunrise accompanied a similar peak in the total organic bromine. These episodes originated in the free troposphere over Greenland. After sunrise the peaks in InorgBr corresponded to O3 depletion periods. InorgBr appeared to be the sum of HBr, HOBr, and Br2. (3) Total organic bromine was relatively constant before sunrise at 100 ng(Br) m−3 but more variable afterward, up to 280 ng(Br) m−3. Individual species include CHBr3 with levels of 7–60 ng(Br) m−3. CH2Br2, CH2ClBr, CHClBr2, and CHCl2Br levels were lower at 0.5–7.5 ng(Br) m−3. CHBr3 was the largest contributor to total organic bromine of the five species, on average accounting for 23%, while the other four species amounted to less than 5% on average. CH3Br (not measured) should contribute 44% of total organic bromine assuming a concentration of 40 ng(Br) m−3 (11 parts per trillion by volume). The remaining contribution was probably from ”missing„ species which were episodically dominant after sunrise with concentrations up to 240 ng(Br) m−3 and may include some inorganic species. All the peaks in the organic bromines after sunrise corresponded to the O3 depletion events. (4) CHBr3, CHClBr2, and CHCl2Br were significantly correlated. The ratio CHClBr2/CHBr3 decreased linearly with increasing In(CHBr3), with a steeper decrease after sunrise than before. The decreases suggest different rates of destruction with CHBr3 having a larger rate constant than CHClBr2. A similar relationship existed between the ratio CHCl2Br/CHClBr2 and the In(CHClBr2), but the dark period slope was near zero, indicating a greater difference in rates in the two species in the light period.