Estimation of hydroxyl radical concentrations in the marine atmospheric boundary layer using a reactive atmospheric tracer

Abstract

Hydroxyl radical (OH) concentrations in the atmospheric boundary layer over a number of remote ocean locations are calculated from the measured diurnal variation in atmospheric dimethylsulfide (DMS). By using averaged DMS data sets from extended periods, the calculation yields OH concentrations averaged over ~riods from several days to weeks. These average OH concentrations range from 7 x 105 to 2.9 x 10 6 molecules cm -3, corresponding to midday maxima of 3 to 12 x 10 6 molecules cm -3. The lowest values correspond to studies with the lowest light intensity (Antarctic summer and South Atlantic winter), and the highest values to regions with probable anthropogenic influence. In addition to the long term averages, daily average OH levels can be calculated for most days in a two week period from a cruise in the tropical eastern Pacific. These calculations are in good argeement with global average OH levels derived from other tracers, and are consistent with model OH calculations when allowance is made for variation in ambient ozone levels between the studies. Estimates of gas exchange made from the diurnal variation of DMS suggest that either the gas exchange coefficient of DMS or the boundary layer mixing depth may have been overestimated in past analyses.

Understanding the oxidation mechanism of methanesulfinic acid by ozone in the atmosphere

“…The oxidation of dimethyl sulfide is considered of great importance in the marine boundary layer, because the main oxidation products, methanesulfonic acid (MSA) and sulfuric acid, can contribute to the formation of non-sea salt sulfate (nss-SO 4 2− ) aerosol, which can act as the cloud condensation nuclei and can promote the formation of marine stratus clouds 4–6 . The reactions with OH radical during the day time 5,7 and with NO 3 radical 5,8,9 in the night initiate the DMS oxidation, and these reactions can be classified as adduct reactions and abstraction reactions. Numerous intermediates such as dimethyl sulfoxide (CH 3 SOCH 3 : DMSO), methanesulfinic acid (CH 3 S(O)OH: MSIA), dimethyl sulfone (CH 3 SO 2 CH 3 : DMSO 2 ) and CH 3 SO x (x = 0−3) radicals can be formed through the subsequent reaction 5,10 .…”

δ13C-CH4 reveals CH4 variations over oceans from mid-latitudes to the Arctic

“…To determine the potential reactive process for CH 4 , the contributions of the OH and Cl radicals were calculated as follows. The average concentrations of the OH and Cl radicals in the marine boundary layer are about 7 × 10 5 –2.9 × 10 6 molecules·cm −3 and 1.8 × 10 4 molecules·cm −3 , respectively 22 23 24 25 ; mean CH 4 concentration is 1.88 ppm; and the rate constant at 8 °C based on the mean sampling temperature for OH and Cl radicals is 4.42 × 10 −15 and 7.59 × 10 −14 cm −3 ·molecules −1 ·S −1 , respectively 26 . Assuming the reactive height is 25 m, based on the sampling height, the CH 4 consumption for OH and Cl radicals is 8.72 × 10 −3 –3.61 × 10 −2 mg·m −2 ·d −1 and 3.85 × 10 −3 mg·m −2 ·d −1 , respectively.…”

An experimental and theoretical study on the reaction of Cl with CF3CF2CH2OH

“…In contrast, in marine and coastal regions at dawn a peak Cl concentration of 1.3 � 10 5 atom cm �3 [5], can be considered in the calculation of � Cl . In remote ocean locations, estimated average OH concentrations range from 7 � 10 5 to 2.9 � 10 6 molecules cm �3 [43] in clean and polluted environments, respectively. Under these local conditions, OH is estimated to be approximately of 7 and 2 months, respectively.…”