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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 s , x contribute as much as the combined contribution of all the measured organic nitrates.

Airborne observations were conducted in the high Arctic (69°N–83°N) during April 6–16, 1992, in support of the Polar Sunrise Experiment. Measurements of temperature, O3, NOx aerosol particles, inorganic aerosol species, inorganic bromide, alkyl nitrate species, and several organohalogens (including bromoform) were made from an altitude of 30 m above ground level (agl) up to 7000 m msl (mean sea level). The average temperature profile shows a strong surface-based inversion up to about 500 m, an isothermal region up to about 1.5 km, and steadily decreasing from 1.5 to 6.8 km. Ozone mixing ratios were frequently found to be depleted from the surface up to various altitudes within the boundary layer (maximum altitude for ozone

Surface mixing ratios of ozone, C2–C6 hydrocarbons, and selected organohalogens were measured at a camp on the Arctic Ocean ice northwest of Ellesmere Island during an 18-day period in April 1992. Ozone was strongly depleted (at or below instrument detection limits of 0.4 parts per billion by volume (ppbv)) more than 40% of the time and exceeded 20 ppbv only during two brief events, in marked contrast to free tropospheric mixing ratios of about 45 ppbv observed at Alert. Alkanes, bromoform, and trichloroethylene, which have been reported to be correlated with O3 at Alert, were found to have mixing ratios at the sea ice surface similar to the levels observed during O3 depletion events at Alert. Meteorological and back-trajectory analyses did not reveal significant correlations with any source region or prevailing local meteorological condition. Elevated mixing ratios of O3 and alkanes over the sea ice were associated with periods of increased dynamic mixing or transport of air from higher altitudes. Prolonged periods of undetectable ozone were correlated with air parcels whose trajectories showed they had been in close proximity to the surface sometime in the previous five days.

Concurrent measurements of total reactive odd nitrogen species (i.e., NOy) and its major components, including organic nitrates, were carried out during 1992 Polar Sunrise Experiment (PSE92) at Alert, Northwest Territories, Canada, to investigate the episodic depletion of surface level ozone following polar sunrise. A series of C3-C7 alkyl nitrates formed from the atmospheric oxidation of hydrocarbons was measured daily during the 13-week study period (January 22 to April 22). In addition, a large number of gas chromatography/electron capture detector (GC/ECD) peaks with retention times greater than those of the hexyl nitrates were also identified as species containing −ONO2 group(s), using a nitrogen specific detector. The total concentrations of these organic nitrates ranged from 34 to 128 parts per trillion by volume and the distribution in the dark period was found to be similar to that found for rural lower-latitude air masses. In contrast to observations made at lower latitudes where alkyl nitrates make a relatively small contribution to NOy, the organic nitrates at Alert were found to contribute between 7 and 20% of the total odd nitrogen species. After polar sunrise the total concentrations of these organic nitrates decreased steadily, due primarily to the consumption of larger (>C4) alkyl nitrates. The C3 alkyl nitrate concentrations showed little variation during this study. During ozone depletion episodes in April there was a positive correlation between the concentration of the larger organic nitrates and ozone. Most surprisingly, the ratio of concentrations of isomeric alkyl nitrates with carbon numbers ≥5, and in particular those involving the C5 isomers, was found to show substantial variations coinciding with the O3 depletion events. This change in the isomeric alkyl nitrate ratios implies a substantial chemical processing of the air masses exhibiting ozone depletion. The possible mechanisms, which must involve consumption of the organic nitrates by either OH radicals or Cl atoms, are discussed in the context of the chemical and meteorological observations conducted at Alert during these ozone depletion events.

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.