Remote troposphere emissions

Biogenic Sulfur Emissions from the Ocean. The ocean is a source of many reduced sulfur compounds to the atmosphere. These include dimethylsulfide (DMS) (2.4.51. carbon disulfide (CS2) (28). hydrogen sulfide (H2S) (291. carbonyl sulfide (OCS) (30.311. and methyl mercaptan (CH3SH) ( ). The oxidation of DMS leads to sulfate formation. CS2 and OCS are relatively unreactive in the troposphere and are transported to the stratosphere where they undergo photochemical oxidation (22). Marine H2S and CH3SH probably contribute to sulfate formation over the remote oceans, yet the sea-air transfer of these compounds is only a few percent that of DMS (2). 

Fig. 3. Tropospheric Concentrations of CXZl, Measured in Remote Locations during December 1980. Calculated concentrations for various postulated atmospheric lifetimes in combination with the upper limit estimated for atmospheric emissions by Simmonda et d. (1983).

Aerosol concentrations and size distributions can be investigated remotely using sun-photometry. Characterization of volcanic aerosol is important in smdies of plume chemistry, atmospheric radiation, and the environmental and health impacts of particle emissions. Watson and Oppenheimer (2000, 2001) used a portable sun-photometer to observe tropospheric aerosol emitted by Mt. Etna. They found distinct aerosol optical signatures for the several plumes emitted from Etna s different summit craters, and apparent coagulation of particles as the plume aged. More recently. Porter et al. (2002) have obtained sun-photometer and pulsed lidar data for the plume from Pu u O o vent on Kilauea, Hawaii, from a moving vehicle in order to build profiles of sulfate concentration. 

Rasmussen et al. 1983). 1,1,1 -Trichloroethane removed by rain water would be expected to re-volatilize rapidly to the atmosphere. Because of its long half-life of 4 years in the atmosphere (see Section 5.3.2.1), tropospheric 1,1,1-trichloroethane will be transported to the stratosphere, where it will participate in the destruction of the ozone layer. It will also undergo long-distance transport from its sources of emissions to other remote and rural sites. This is confirmed by the detection of this synthetic chemical in forest areas of Northern and Southern Europe and in remote sites (Ciccioli et al. 1993). 

Carbon monoxide (CO) is also formed in aquatic environments from the photochemical degradation of DOM [3,4,8,22,94-105]. Strong gradients of CO have been observed in the lowest 10 metres of the atmosphere over the Atlantic Ocean [97]. The samples nearest the ocean surface were some 50 ppb higher than at the 10-metre altitude-sampling inlet. This implies that the ocean is a source of CO to the atmosphere and that this source can increase the atmospheric concentration. CO is reactive in the troposphere and thus its emissions from the ocean may influence the hydroxyl radical (OH) and ozone concentrations in the marine atmospheric boundary layer that is remote from strong continental influences. 

As noted in Chapter 4, the dimensionless product x = beM z is called the optical depth of the layer, and (15.26) is called the Beer-Lambert law. In the visible portion of the spectrum, optical depth of tropospheric aerosols can range from less than 0.05 in remote, pristine environments to close to 1.0 near the source of intense particulate emissions such as in the plume of a forest fire. 

Tropospheric O3 concentrations appear to be increasing as a result of increased direct emissions of NO, hydrocarbons, and CH4. Because of the role of NO in partitioning HO and because of the large variation in the concentration of NO between remote oceanic areas and continental areas, an increase in O3 by a factor of 2 has been estimated to increase OH by perhaps 10% over ocean areas and by probably more than 10% over the continents (Thompson et al. 1989). These changes might, of course, feed back on the concentration perturbation of O3. 

VOCs, ozone and other pollutants can be transported by wind to regions remote from the site of emission. Tropospheric ozone formation is therefore a regional rather than a local issue. 

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