Troposphere clouds

The use of the sun or moon as the light source allows one to measure the total column abundance, i.e., the concentration integrated through a column in the atmosphere. This approach has been used for a number of years (e.g., see Noxon (1975) for NOz measurements) and provided the first measurements of the nitrate radical in the atmosphere (Noxon et al., 1978). As discussed later in this chapter, such measurements made as a function of solar zenith angle also provide information on the vertical distributions of absorbing species. Cloud-free conditions are usually used for such measurements as discussed by Erie et al. (1995), the presence of tropospheric clouds can dramatically increase the effective path length (by an order of... 

Erie, F., K. Pfeilsticker, and U. Platt, On the Influence of Tropospheric Clouds on Zenith-Scattered-Light Measurements of Stratospheric Species, Geophys. Res. Lett., 22, 2725-2728 (1995). 

The aerosols of sulfuric acid so formed increase the reflectivity (albedo) of the Earth s atmosphere, cutting down the solar radiation that reaches the Earth s surface and so counteracting to some extent the greenhouse warming due to CO2 emissions that accompany the SO2, as mentioned earlier. Airborne sulfuric acid may be neutralized by traces of ammonia in the air, giving particulate NH4HSO4 and (NH4)2S04 hazes, but in the absence of such neutralization the aqueous sulfuric acid droplets in tropospheric clouds may reach pH 1.5 or lower. 

ABLE (AirBome Lidar Experiment) is a Nd-Yag high energy lidar for the measurement of aerosols and PSC. It will operate in either a dual wavelength configuration 532 nm or 355 nm emissions or at 532 nm with dual polarisation detection capacity. It will detect aerosols, PSC and tropospheric clouds. 

The final step in removal of any species from the atmosphere involves heterogeneous deposition to the Earth s surface. Removal processes include wet deposition via rain-out (following uptake into tropospheric clouds) and dry deposition to the Earth s surface, principally to the oceans. The rates of these processes are largely determined by the species chemistries in aqueous solution. Heterogeneous lifetimes of the parent HFCs, HCFCs and HFEs are of the order of hundreds of years because of their low aqueous solubility and reactivity. 

As seen from Table 8, heterogeneous removal of halocarbonyl species is rapid and is dominated by tropospheric cloud rain-out. 

Extrapolation to the K/T boundary requires consideration of the time scales of acid deposition. Nitric acid formation occurs rapidly by aqueous phase reaction of NO and NO2 with liquid water produced by tlie incident K/T bolide on both impact and infall of ejecta. For tlie quantities of NO produced by the K/T impact ( 10 5 moles), conversion to HNO3 occurred wiUiin days, assuming sufficient liquid water was available in the posl-K/T atmosphere. The nitric acid will form an acid rain of pH 0 for a liquid water content of 1 g/m (typical of tropospheric clouds) but will contain enough protons to weather only 3 x 10 moles of Sr, for Sr/(Ta -0.003 in soil and bedrock minerals. Sulfuric acid formation occurred on a time scale of years [7] due to the slow rate of gas phase SO2 oxidation. Spread evenly over 10 years, 10 moles of SO2 produced a global acid rain of pH —4, and released —3 x 10 moles of Sr. 

Sion In Nonurban Tropospheric Clouds," Atmos. Environ. 1983, 17 341-345. — ... 

Maahs, H. G. (1983), Measurements of the Oxidation Rate of Sulfur (IV) by Ozone in Aqueous Solution and Their Relevance to S02 Conversion in Nonurban Tropospheric Clouds, Atmos. Environ. 17, 341-345. 

Atmospheric chemistry is dominated by trace species, ranging in mixing ratios (mole fractions) from a few parts per million, for methane in the troposphere and ozone in the stratosphere, to hundredths of parts per trillion, or less, for highly reactive species such as the hydroxyl radical. It is also surprising that atmospheric condensed-phase material plays very important roles in atmospheric chemistry, since there is relatively so little of it. Atmospheric condensed-phase volume to gas-phase volume ratios range from about 3 x KT7 for tropospheric clouds to 3 x ICE14 for background stratospheric sulfate aerosol. 

Maahs, H. G Kinetics and mechanism of the oxidation of S(IV) by ozone in aqueous solution with particular reference to S02 conversion in nonurban tropospheric clouds. /. Geophys. Res. 88, 10721 (1983). 

The occurrence of clouds shows dramatic geographical variation and is generally restricted to the lowest 4-6 km of the troposphere. Clouds form and evaporate repeatedly. Only a small fraction (around 10%) of the clouds that form actually generate precipitation. Thus nine out of ten clouds evaporate without ever generating rain droplets. Even in cases where precipitation develops, the raindrops often evaporate on their way falling through the cloud-free air, so the drops never reach the surface. 

N0 typically ranges between 50 and 500 cm-3. rm ranges between 5 and 25 pm, and values of P = 2 and 5 have been used for tropospheric clouds. Consider rm = 20 pm and an optical pathlength of 1 m. Calculate and plot (a) the size distribution and (b) the transmission of light through a droplet population with this modified gamma distribution for both p = 2 and 5. For the plot of T(X), consider Mj ranging from 0 to 800 cm-3. Identify the sensitivity of the number concentration at which T = 0.5 to the two values of p. [The size distribution can be plotted as n(r)/No.]... 

Our discussion in the preceding sections has focused on warm nonraining tropospheric clouds. Water in the atmosphere can also exist as ice, rain, snow, and so on. We summarize here aspects of the formation and removal of these water forms that are most associated with atmospheric chemistry. The interested reader is referred for more information to Pruppacher and Klett (1997) and references therein. 

Liittke, I, Scheer, V, Levsen, K., Wunsch, G, Cape, J. N., Hargreaves, K. X, Storeton-West, R. L., Acker, K., Wieprecht, W. and B. Jones (1997) Occurrence and formation of nitrated phenols in and out of clouds. Atmospheric Environment 31, 2637-2648 Lymar, S. V, V. Shafirovich and G. A. Poskrebyshev (2005) One-electron reduction of aqueous nitric oxide a mechanistic revision. Inorganic Chemistry 44, 5212-5221 Maahs, H. G. (1983) Measurement of the oxidation rate of sulphur(IV) by ozone in aqueous solution and their relevance to SO2 conversion in nonurban tropospheric clouds. Atmospheric Environment 17, 341-345... 

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