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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 ...

A highly selective and sensitive detector for measuring organic nitrates in atmospheric air samples has been developed. This detector is based on the luminol chemiluminescence-based detection of NO 2 produced by postcolumn thermal decomposition of organic nitrates. Determination of the relative detector sensitivities to C 3 -C 6 alkyl nitrates, α,β-hydroxy nitrates, α,β-dinitrates, and several mono- and multinitro aromatic compounds as well as N-nitrosodimethylamine has been conducted. The detector is shown to produce one NO 2 per molecule at a pyrolysis temperature of 350 o C, yielding identical sensitivities for alkyl and hydroxy nitrates, consistent with the known thermal decomposition pathway and thermal lifetimes at this temperature

Ambient measurements of multifunctional organic nitrates have become necessary to understand the complete tropospheric NO y budget. Laboratory studies indicate that multifunctional organic nitrates that are produced from OH and NO 3 reaction with alkenes may be important; however, they have yet to be detected in atmospheric samples. We have synthesized several C 3 -C 6 alkyl nitrates, α,β-hydroxynitrates, and dinitrates that are produced from oxidation of atmospheric hydrocarbons

Alkyl nitrates (C3C6), NO, NO2, HNO3 and PAN were measured at a rural site in Ontario from 26 March to 27 April 1990. A series of nine alkyl nitrates were measured daily at this site. The sum of the concentrations of these alkyl nitrates ranged from 29 to 87 ppt. The alkyl nitrates were found to contribute, on average, only 1.8% of the sum of the odd nitrogen species. In this paper, we discuss the observed distribution of the alkyl nitrates in light of the relative formation and removal processes. The observed concentration distribution is consistent with the relative formation rates calculated using the observed alkane concentrations, although it is somewhat skewed toward the lower molecular weight nitrates. The importance of the alkyl nitrates, relative to multifunctional organic nitrates that are produced from OH reaction with alkenes, is discussed.

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.

The occurrence of Norrish type-I α-cleavage has been established in β-dithiolactones, involving the n-π* singlet state (diradical and carbene reactive intermediates). Concerted ring expansion to a thiacarbene from the excited state is suggested to be responsible for the formation, at least in part, of one of the cyclic thioacetals. Although this α-cleavage process is similar to that of corresponding β-lactones, the behaviour of the resulting intermediates is different.

Photochemical \alpha -cleavage from the lowest triplet state $(n\pi^*, T_1)$, resulting in the generation of a diradical intermediate, appears to be general for cyclobutanethiones. The diradical intermediate derived from 1,3-dithione is observed to undergoes ring expansion to carbene or close to either dithione or dithiolactone. The Photochemical behavior reported here for cyclobutanethiones is different from that of the corresponding cyclobutanones. \alpha-Cleavage processes in the case of cyclobutanethiones are not efficient and are often accompanied by side reactions.

Organized media such as micelles have shown great promise in achieving regio- and stereoselectivity in photochemical cycloaddition reactions as has been shown by recent reports. 7-Alkoxy- and 4-methyl-7-alkoxycoumarins dimerize in organic solvents to give the syn head-tail dimer. However, dimerization of these coumarins in SDS and CTAB micelles did not show any reversal in this trend. The results probably indicate that the micellar orientational effect is most effective only in those systems where the forces that control regiochemistry are weaker than hydrophobic association energies.

The photochemical and photophysical processes of many organic compounds are a function of the environment in which they are present. In this connection we have chosen to investigate the environmental perturbations on the photodimerization of coumarin,l and the results of our study in aqueous and micellar media are presented in this paper. Coumarin has historically been the subject of intense photochemical and spectroscopic interest, mainly as a consequence of its importance in biological systems. Coumarin has been chosen for our investigation as its fascinating photochemical behavior has been fairly well explored,2 and therefore the environmental influence, which is the subject of our concern, would be easily understandable.

Preferential yield of ring expansion and rearrangement products through α-cleavage of tetramethyl-3-thio-1,3-cyclobutanedione (1) and 3-mercapto-2,2,4-trimethyl-3-pentenoic acid β-(thio lactone) (2) involving diradical and carbene has been observed upon photolysis of 1 and 2.

7-Alkoxy and 4-methyl-7-alkoxy coumarins show solvent-dependent fluorescence emission. The monomeric fluorescence emission of these alkoxy coumarins was exploited as a probe to measure the surface polarity of the micelles formed by ionic (sodium dodecylsulphate and cetyltrimethyl-ammonium bromide) and non-ionic (Triton X-100) detergents. By comparing the solvent-dependent fluorescence of these alkoxy coumarins in various homogeneous solvents, the polarity of the micelles was determined qualitatively. All three micelles are more polar than hydrocarbon solvents but are less polar than water.

The singlet state photophysical properties of two sets of substituted alkylbenzenes have been determined in solution. The compounds studied are Ar(CH 2 ) n X where X = H, CH 3 , OH, CN, NH 2 , and CO 2 CH 3 , and n = 1 or 2. For n = 1, both k f and k ic (but not k isc ) show modest trends which may be related to substituent electronegativity; none of these rates are affected in a systematic fashion when n = 2. An amino group increases k ic in both series, presumably through intramolecular exciplex formation. An ester group enhances both ki ic and k isc when n = 1, due to the introduction of n,π ★ character into the first excited singlet state.

Preferential yield of ring expansion and rearrangement products through α-cleavage of tetramethyl-3-thio-1,3-cyclobutanedione (1) and 3-mercapto-2,2,4-trimethyl-3-pentenoic acid β-(thio lactone) (2) involving diradical and carbene has been observed upon photolysis of 1 and 2.

Thioketones and dithioesters, using 1,3-cyclobutanedithione and 3-mercapto-2,2,4-trimethyldithio-3-pentenoic acid B-thiolactone as models are found to undergo a-cleavage to give the diradical and carbene as reactive intermediates.

The dithiolactone (1) upon excitation gives the dithione (2) in cyclohexane and other aprotic solvents and a 1 : 1 adduct in hydroxylic solvents from an nπ* excited singlet state via an α-cleavage process.