Non-sea salt sulfate

Figure 9.35 shows a typical set of mass size distributions for total suspended particles (TSP), Na, Cl, Al, V, NO-, S04, and NH4 at Chichi in the Ogasawara (Bonin) Islands, about 1000 km southeast of the main island of Japan (Yoshizumi and Asakuno, 1986). As expected for a marine site such as this, Na and Cl from sea salt predominate, and both the TSP and Na and Cl components peak in the coarse particle range. Al is also found primarily in the larger particles and is attributed to a contribution from soil dust. On the other hand, vanadium, non-sea salt sulfate (nss-S04 ), and ammonium are primarily in the fine particles. The vanadium levels are extremely low and likely reflect long-range transport of an air mass containing the products of combustion of fuel oil, which contains V because it is likely associated with a combustion source, it would be expected in the fine particle mode, consistent with Fig. 9.35. 

Li-Jones, X., and J. M. Prospero, Variations in the Size Distribution of Non-Sea-Salt Sulfate Aerosol in the Marine Boundary Layer at Barbados Impact of African Dust, J. Geophys. Res., 103, 16073-16084 (1998). 

Savoie, D. L., J. M. Prospero, and E. S. Saltzman, Non-Sea-Salt Sulfate and Nitrate in Trade Wind Aerosols at Barbados Evidence for Long-Range Transport, J. Geophys. Res., 94, 5069-5080 (1989). 

The seasonal cycle of CCN has also been shown to be correlated with that of cloud optical depth in one remote marine area (Boers et al., 1994), and the isotope composition of non-sea salt sulfate over remote regions of the southern Pacific Ocean has been shown to be consistent with a DMS source (Calhoun et al., 1991). 

A number of field studies have quantitatively examined the relationship between the CCN number concentration and/or cloud droplet concentration and the mass concentration of non-sea salt sulfate (nss). Figure 14.45 shows one summary of some of these studies in the form of a log-log plot (Van Dingenen et al., 1995). Given the variety of measured parameters and wide range of conditions encompassed by these data (CCN... 

Once DMS is emitted into the atmosphere it will eventually be oxidized by OH or NO3 radicals to sulfur dioxide (SO2), methanesulfonic acid (MSA), and, via SO oxidation, to non-sea-salt sulfate (nss-S042 ) as major reaction products (e.g. 10.111. The Southern Ocean represents a relatively unpolluted marine environment. It offers a unique possibility to study the natural sulfur cycle in an atmosphere far remote from man-inhabited continents. 

Another link between halogen and sulfur chemistry is the formation of S(VI) within particles. Aerosol particles grow, among other processes, by uptake of SO2 in cloud droplets where it is oxidized to sulfate. The most important aqueous phase oxidants for S(IV) are often thought to be H2O2 and O3 (e.g., Seinfeld and Pandis, 1998) with O3 being important only for pH > 6. Some authors state that oxidation by O3 is the dominant process for the formation of non-sea-salt sulfate in sea salt particles... 

NH3 and to a lesser extent mono-, di-, and trimethylamines are the only significant gaseous bases in the atmosphere, and there has been considerable interest in whether the oceans are a source or sink of these gases. Early attempt to assess the air-sea flux from concentration measurements are probably suspect because of the ease with which sample contamination can occur during laboratory processing and analysis. It should be noted here that due to its high solubihty (low value of Henry s law constant), the air-water transfer of NH3 (and the methylamines for the same reason) is under gas phase control (see Section 6.03.2.1.1). The first reliable measurements were probably from the North and South Pacific and indicated that the flux of NH3 from sea to air is of a size similar to that for emission of DMS (Quinn et al., 1990, 1988). Indeed, the authors showed that this similarity was mirrored in the molar ratio of (non-sea-salt) sulfate to ammonium (1.3 0.7) in atmospheric aerosol particles collected on the cruise, indicating that for clean marine air remote from terrestrial sources, the emission of DMS and NH3 from the sea appears to control the composition of the aerosol. 

Size distribution of the number (N) and volume (V) of excess (non sea salt) sulfate and sea salt particles with r S 0.03 pm. (Data of A. Meszaros)... 

Savoie, D. L., and Prospero, J. M. (1989) Comparison of oceanic and continental sources of non-sea-salt sulfate over the Pacific ocean. Nature, 339,685-687. 

Zakey AS (2008) Seasonal and spatial variation of atmospheric particulate matter in a developing megacity, the Greater Cairo, Egypt. Atmosfera 21 171-189 Zhuang H, Chan CK, Fang M et al (1999) Formation of nitrate and non-sea-salt sulfate on coarse particles. Atmos Environ 33 4223-4233... 

The BC aerosol and fly ash are unquestionably human produced because natural sources are negligible. Likewise, non-sea-salt sulfate can be largely attributed to anthropogenic sources. Filter samples collected on board the RA Brown in the clean marine boundary layer south of the FTCZ reveal a fine aerosol sulfate concentration of about 0.5 pg/m, probably from the oxidation of naturally emitted... 

The prineipal eonstituent of marine particles are sea salt, non-sea-salt sulfate (nss sulfate), and mineral dust (38). The nss sulfate has both a continental and marine souree and is derived from homogeneous nucleation and diffusive mass transport proeesses of aerosol precursor gases, such as SO2 and NH3. Numerous studies have shown that the accumulation mode in clean marine air is predominately composed of nss sulfate. Its concentration decreases from coastal regions of the continents to the remote areas of the oceans. Single-particle analysis by electron microscopy showed that most of the particles are morphologically similar to (NH4)2S04 (39,40). Also a small number of H2SO4 particles were found. 

---