Troposphere marine

MODerate resolution Imaging Spectroradiometer Measurements Of Pollution In The Troposphere Marine Observation Satellite... 

Kritz, M. A. (1982). Exchange of sulfur between the free troposphere, marine boundary layer and the sea surface. J. Geophys. Res. 87, 8795-8803. 

Another interesting applieation of MDGC is in the rapid determination of isoprene (the most reaetive hydroearbon speeies) and dimethyl sulfide (DMS) (the major souree of sulfur in the marine troposphere and a preeursor to eloud formation) in the atmosphere (16). The deteetion limits were 5 and 25 ng 1 respeetively. 

When NMHC are significant in concentration, differences in their oxidation mechanisms such as how the NMHC chemistry was parameterized, details of R02-/R02 recombination (95), and heterogenous chemistry also contribute to differences in computed [HO ]. Recently, the sensitivity of [HO ] to non-methane hydrocarbon oxidation was studied in the context of the remote marine boundary-layer (156). It was concluded that differences in radical-radical recombination mechanisms (R02 /R02 ) can cause significant differences in computed [HO ] in regions of low NO and NMHC levels. The effect of cloud chemistry in the troposphere has also recently been studied (151,180). The rapid aqueous-phase breakdown of formaldehyde in the presence of clouds reduces the source of HOj due to RIO. In addition, the dissolution in clouds of a NO reservoir (N2O5) at night reduces the formation of HO and CH2O due to R6-RIO and R13. Predictions for HO and HO2 concentrations with cloud chemistry considered compared to predictions without cloud chemistry are 10-40% lower for HO and 10-45% lower for HO2. 

A high-speed sensor for the assay of dimethyl sulfide in the marine troposphere based on its CL reaction with F2 was recently reported [18]. Sample air and F2 in He were introduced at opposite ends of a reaction cell with a window at one end. The production of vibrationally excited HF and electronically excited fluorohydrocarbon (FHC) produced CL emission in the wavelength range 450-650 nm, which was monitored via photon counting. Dimethyl sulfide could be determined in the 0-1200 pptv (parts per trillion by volume) concentration range, with a 4-pptv detection limit. 

Aerosol surface area is likely to be variable even within a remote marine air mass. Previous MBL aerosol studies describe changes in aerosol concentration and composition due to entrainment from the free troposphere (Bates et al., 1998, 2001 Covert et al., 1998). Raes et al. (1997) found an observable link between vertical transport patterns and aerosol variability in the MBL specifically in the Aitken mode (<0.2/u.m). Hence entrainment of aerosol from the free troposphere appears to occur frequently, even in remote MBL air masses. In addition, aerosols have the capacity to travel great distances in the free troposphere, before being entrained into the MBL. 

Raes, F., VanDingenen, R., Cuevas, E., VanVelthoven, P. F. J., and Prospero, J. Observations of aerosols in the free troposphere and marine boundary layer of the subtropical Northeast Atlantic Discussion of processes determining their size distribution, J. Geophys. Res.-A., 102, 21 315-21 328,1997. 

Marine mercury cycle. All fluxes are in units of Mmol/y. Preindustrial fluxes are in parentheses. The marine boundary layer is the iower part of the troposphere in which mercury transformations associated with the air-sea interface occur. Source After Mason, R. R, and G.-R. Sheu (2002). Global Blogeochemical Cycles 16, GB001440. 

Figure 4.34 compares the absorption spectra of the diatomic halogens, F2, Cl2, Br2, and I2. Cl2 is of particular recent interest in the troposphere in that levels up to 150 ppt have been observed in marine areas (Keene et al., 1993 Pszenny et al., 1993 Spicer et al., 1998). Table 4.30 summarizes the absorption cross sections of Cl2, Br2, and BrCl (DeMore et al., 1997 Marie et al., 1994 Hubinger and Nee, 1995). These diatomics all dissociated with a photodissociation quantum yield of 1 (Calvert and Pitts, 1966). 

Ganske, J. A., H. N. Berko, and B. J. Finlayson-Pitts, Absorption Cross Sections for Gaseous C1N02 and Cl2 at 298 K Potential Organic Oxidant Source in the Marine Troposphere, J. Geophys. Res., 97, 7651-7656 (1992). 

Laux, J. M., J. C. Hemminger, and B. J. Finlayson-Pitts, X-ray Photoelectron Spectroscopic Studies of the Heterogeneous Reaction of Gaseous Nitric Acid with Sodium Chloride Kinetics and Contribution to the Chemistry of the Marine Troposphere, Geophys. Res. Let., 21, 1623-1626 (1994). 

Let us first review the oxidants that have been recognized for some time as important in the troposphere, as well as atomic chlorine, for which there is increasing evidence of a contribution in marine regions. 

Based on this chemistry, the production rate of 03 is expected to be very sensitive to the NO concentration, increasing with NO (see also Chapter 16 for a discussion of the dependence of 03 generation on NOx). In this context, Folkins et al. (1998) suggest that acetone is likely the major contributor to enhanced ozone production in the upper troposphere, since increased CH3OOH and H202 concentrations at 9- to 12-km altitude were observed only at very small NO concentrations, indicative of clean marine boundary layer air under such low NOx conditions, destruction rather than production of 03 is expected. 

Finlayson-Pitts, B. J., Chlorine Atoms as a Potential Tropospheric Oxidant in the Marine Boundary Layer, Res. Chem. Interned., 19, 235-249 (1993). 

Fate Urban Remote marine Free troposphere Nonurban continental... 

Measurements of HN03 in the marine boundary layer are typically of the order of tens to hundreds of ppt. For example, Heikes et al. (1996) reported average concentrations of 160 ppt, with a range from 30 to 280 ppt. In the middle and upper troposphere, concentrations of 100-400 ppt have been reported (e.g., Singh et al., 1998). 

Sauer, F., S. Limbach, and G. K. Moortgat, Measurements of Hydrogen Peroxide and Individual Organic Peroxides in the Marine Troposphere, Atmos. Environ., 31, 1173-1184 (1997). 

Zhou, X., and K. Mopper, Carbonyl Compounds in the Lower Marine Troposphere over the Caribbean Sea and Bahamas, J. Geophys. Res., 98, 2385-2392 (1993). 

Raes, F., Entrainment of Free Tropospheric Aerosols as a Regulating Mechanism for Cloud Condensation Nuclei in the Remote Marine Boundary Layer, J. Geophys. Res., 100, 2893-2903 (1995). 

Raes, F., R. Van Dingenen, E. Cuevas, P. F. J. Van Velthoven, and J. M. Prospero, Observations of Aerosols in the Free Troposphere and Marine Boundary Layer of the Subtropical Northeast Atlantic Discussion of Processes Determining Their Size Distribution, J. Geophys. Res., 102, 21315-21328 (1997). 

Chameides and co-workers (1992) examined the observed concentrations of ozone and its precursors, NOx and VOC, in a variety of tropospheric locations, from remote marine areas to polluted urban regions. Figure 16.38 shows ranges of observed NOx and OH-reactivity adjusted VOC (expressed relative to propene) in four... 

Figure 2. Ozone profiles in the tropics show the contrasts between dry and wet seasons, and between continental and marine sites. Episodes of extremely high ozone concentrations, now seen over the Atlantic, are unlike anything reported before. These air pockets must somehow be getting in the troposphere from the stratosphere.

---