Tropospheric composition

In addition, as seen in Fig. 13.9, changes in tropospheric composition can also impact the results. For example, the trend in total ozone over 20 years measured in Belgium was -1.38 + 0.50% per decade but after correcting for changes in tropospheric S02, no significant trend in ozone could be discerned (De Muer and De Backer, 1992). There is also a concern regarding the effects of trends in tropospheric aerosols on the derived trends in 03. 

Tang, X. and S. Madronich (1994) Effects of increased solar UVR on tropospheric composition and air quality, Chapter 6, UNEP publ. (Ed. J.C. van der Leun). 

Another important goal of a tropospheric chemistry research program should be to establish a global air sampling network to characterize the distribution of atmospheric compounds today. In order to determine if the tropospheric composition is changing, a commitment must be made to maintain this network into the 21st century. The interchange of... 

The aim of this section is to discuss the modifications of the atmospheric composition which can be related to the variations of the radiation balance and temperature observed in this century. We shall first deal with the relation between short-range modifications of atmospheric (stratospheric and tropospheric) composition and the transfer of incoming radiation. After this discussion, atmospheric factors influencing the absorption of infrared radiation emitted by the Earth s surface will be presented briefly. 

In the last subsection the relation between short-wave radiative transfer and tropospheric composition changes has been presented. The aim of this subsection is to discuss the interaction between infrared radiation emitted by the Earth s surface and variations in the chemical composition of the troposphere. Since the influence of aerosol particles on infrared radiative transfer is not clear and is sometimes neglected,4 this paragraph is devoted to the effects of the carbon dioxide increase, which seems to be a very important environmental factor. 

The IMAGES model has been used to assess the impact of human activities on the chemical composition of the global troposphere. To tiuantify past, current, and future changes in tropospheric composition, IMAGES was used to simulate the preindustrial atmosphere (year 1850), a contemporary atmosphere (year 1990), and a future atmosphere (year 2050), respectively. As expected, the largest increase in ozone occurs in the lower troposphere in the Northern Hemisphere with changes of more than 70% at mid-... 

S.R. Wilson, K.R. Soloman, X. Tang, Changes in the tropospheric composition and air quality due to stratospheric ozone depletion and climate change, Photochem. Photobiol. Sci. 6 (3) (2007) 301-310. 

Hauck G and Arnold F 1984 Improved positive-ion composition measurements in the upper troposphere and lower stratosphere and the detection of acetone Nature 311 547-50... 

The gaseous composition of unpolluted tropospheric air is given in Table 2-1. Unpolluted air is a concept, i.e., what the composition of the air would be if humans and their works were not on earth. We will never know the... 

Has the composition of the unpolluted air of the troposphere most probably always been the same as in Tables 2-1 and 2-2 Will Tables 2-1 and 2-2 most probably define unpolluted air in the year 2085 Discuss your answer. 

The transformation of arenes in the troposphere has been discussed in detail (Arey 1998). Their destruction can be mediated by reaction with hydroxyl radicals, and from naphthalene a wide range of compounds is produced, including 1- and 2-naphthols, 2-formylcinnamaldehyde, phthalic anhydride, and with less certainty 1,4-naphthoquinone and 2,3-epoxynaphthoquinone. Both 1- and 2-nitronaphthalene were formed through the intervention of NO2 (Bunce et al. 1997). Attention has also been directed to the composition of secondary organic aerosols from the photooxidation of monocyclic aromatic hydrocarbons in the presence of NO (Eorstner et al. 1997) the main products from a range of alkylated aromatics were 2,5-furandione and the 3-methyl and 3-ethyl congeners. 

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. 

Lehrer, E., D. Wagenbach, and U. Platt, Aerosol Chemical Composition during Tropospheric Ozone Depletion at Ny Alesund/Svalbard, Tellus, 49B, 486-495 (1997). 

The data in Table 9.11 are based on an extensive review of the literature through 1985 by Milford and Davidson (1985). Because they represent composites of many different studies carried out in many different locations by many different investigators, they will not match any particular sample of airborne particulate matter indeed, for many of these elements, the size distribution is multimodal, which is not reflected in the median values shown in Table 9.11. On the other hand, such data demonstrate very clearly some characteristics of tropospheric particles that are common to many conditions. 

In short, while there are many common elements and size distributions in tropospheric particles found in many areas around the world, it is important to recognize that in some circumstances, the particle composition and size distributions may be unique. 

---