Aerosol, sulfuric

Alternatively, in the presence of particulate matter and aerosols, sulfur dioxide may react with atmospheric oxygen to form sulfur trioxide, which forms sulfuric acid, a strong acid, in water ... 

Hering, S. V., and S. K. Friedlander, Origins of Aerosol Sulfur Size Distributions in the Los Angeles Basin, Atmos. Environ 11 2647-2656 (1982). 

Surface Chemical Analysis. Electron spectroscopy of chemical analysis (ESCA) has been the most useful technique for the identification of chemical compounds present on the surface of a composite sample of atmospheric particles. The most prominent examples Include the determination of the surface chemical states of S and N in aerosols, and the investigation of the catalytic role of soot in heterogeneous reactions involving gaseous SO2, NO, or NH3 (15, 39-41). It is apparent from these and other studies that most aerosol sulfur is in the form of sulfate, while most nitrogen is present as the ammonium ion. A substantial quantity of amine nitrogen also has been observed using ESCA (15, 39, 41). 

It was found that the requirements were satisfied for application of the linear regression technique to species mass concentrations in a multicomponent aerosol. The results of 254 particle size distributions measured at China Lake in 1979 indicate that the normalized fine aerosol volume distribution remained approximately constant. The agreement between the calculated and measrued fine particle scattering coefficients was excellent. The measured aerosol sulfur mass distribution usually followed the total distribution for particles less than 1 ym. It was assumed that organic aerosol also followed the total submicron distribution. 

Because the FPD responds to both aerosol and gaseous sulfur species, it has also been possible to modify these instruments to continuously measure aerosol sulfur by selectively removing gaseous sulfur compounds with a lead(II) oxide-glycerol coated denuder (55). Use of such an instrument for airborne measurements of aerosol sulfur in and around broken clouds has been reported (57). In principle, speciation between aerosol sulfate, disulfate, and sulfuric acid by selective thermal decomposition (58, 59) can also be achieved. Flame photometric detectors have also been used as selective detectors for gas chromatography. Thornton and Bandy (60) reported the use of a chromatographic system with a flame photometric detector for airborne measurement of S02 and OCS with a detection limit of 25 pptrv. 

One adaptation of this approach uses a further temperature cycle to 220 °C, which volatilizes ammonium sulfate and bisulfate in aerosols but not nonvolatile sulfates (e.g., Na2S04) (37, 40). Ammonium bisulfate and ammonium sulfate are not differentiated by this approach. Another adaptation collects the aerosol sulfuric acid on a heated denuder tube (38) for —15 min, then removes it thermally for FPD analysis while collecting another sample on a second denuder tube. Because the sample is preconcentrated in this approach, the more sensitive version of the FPD is not required. 

Methanesulfonic acid, although it comprises a relatively small fraction of total non sea-salt aerosol sulfur, has been shown (2) to be a ubiquitous component of marine aerosols. Its occurrence and distribution have been suggested as of use as an in situ tracer (3.4) for oceanic emissions and subsequent reaction and deposition pathways of organosulfur compounds and dimethyl sulfide in particular. 

The processes by which clouds incorporate sulfuric and nitric acids are conveniently distinguished into two categories depending upon whether oxidation takes place in the gas phase or in the aqueous phase, as illustrated schematically in Figure 1. For an examination of gas-phase atmospheric oxidation of SO2 and NO2 see (1,2). Products of this oxidation, aerosol sulfuric acid and sulfat and nitrate salts, and gas-phase nitric acid, are expected to be rapidly and to great extent incorporated into cloud droplets upon cloud formation 0,4). 

In the fourth type of identification the chemical composition of particles is studied in situ. By suitable chemical aerosol instruments the concentration and the size distribution of certain elements can be continuously monitored. The flame photometry of sodium containing particles (e.g. Hobbs, 1971) is a good example for such a method. Recently flame photometric detectors have also been developed to measure aerosol sulfur in the atmosphere (e.g. Kittelson et at., 1978). 

Figure 2.5. Reactive uptake coefficient (7) for several stratospheric heterogeneous processes as a function of temperature and aerosol sulfuric acid weight percentage. Values established for atmospheric conditions representative of the lower stratosphere pressure of 50 hPa, 5 ppmv H2O, 2 ppbv HC1 and 0.1 ppbv CIONO2. Aerosol diameter of 10 5cm. After JPL (2000).

Hering, S.V., Friedlander, S.K. (1982). Origins of aerosol sulfur size distributions in the Los Angeles basin. Atmos. Environ. 11, 2647-2656. 

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