Aerosol concentration trend

At Arosa, Switzerland, where there are records back to 1926 (the longest data record available), the trend in annual mean 03 has been determined to be —(2.3 + 0.6)% per decade. When contributions due to the solar cycle, temperature, and stratospheric aerosol concentrations are taken into account, the trend is —(1.9 0.6)% per decade. However, the total measured column 03 includes both stratospheric and a smaller tropospheric contribution, and the latter has been increasing (see Chapters 14 and 16). This would tend to mask part of a decrease in stratospheric 03. Applying an estimate of the increase in tropospheric ozone gives a trend in stratospheric 03 of - (3.0 + 0.6)% per decade at Arosa (Staehelin et al., 1998b). 

In short, changes in aerosol concentrations over industrialized regions can complicate the interpretation of UV trends (e.g., see Justus and Murphey, 1994). The same is true of clouds, which play a major role in the... 

The condensed phases also are important to the physical processes of the atmosphere however, their role in climate poses an almost entirely open set of scientific questions. The highest sensitivity of physical processes to atmospheric composition lies within the process of cloud nucleation. In turn, the albedo (or reflectivity for solar light) of clouds is sensitive to the number population and properties of CCN (Twomey, 1977). At this time, it appears impossible to predict how much the temperature of the Earth might be expected to increase (or decrease in some places) due to known changes in the concentrations of gases because aerosol and cloud effects cannot yet be predicted. In addition, since secular trends in the appropriate aerosol properties are not monitored very extensively there is no way to know... 

The carbon analyzer has been used to analyze filters from 42 urban sites and 22 non-urban sites in the United States. These filters were obtained from the National Air Surveillance Network (NASN) filter bank for 1975. Carbon concentrations and mass fractions for Detroit, Michigan, are shown in Figures 5 and 6. Both the organic and elemental carbon concentrations are highly variable, and no seasonal trends are apparent. For this site elemental carbon constituted 38% of total aerosol carbon. Typical values for other sites ranged between 35 and 55%. 

Figure 4 presents particle size distributions for six elements which differ among themselves and also from those in Figure 3. Somewhat subjectively, we may identify three patterns in these distributions (a) A coarse mode, typified by Ca and the other elements of Figure 3, which may represent a terrestrial dust origin. This mode can account for coarse particle concentrations observed for Fe, K, Mn, and S. (b) A fine mode with somewhat greater concentrations in the 0.5-1 ymad fraction than in 1-2 ymad particles. The amounts in this <2 ymad range, in excess of those which can be attributed to a coarse crustal aerosol tail with the Ca distribution, show similarities in particle size distributions for Zn, Mn, and possibly Fe. Since the trends shown in Figure 2 point to these elements being characteristic of large scale air masses, their fine modes may be principally due to natural processes.

Although the increase in stratospheric sulfate aerosols after volcanic eruptions is dramatic, there is some evidence that these events may be superimposed on a longer term trend to increased stratospheric sulfate concentrations (Hofmann, 1990). Whether this is due to increased anthropogenic or natural sources such as COS or to an increased residual volcanic layer, i.e.,... 

A similar relationship was observed in Germany. Figure 12.36, for example, shows the deviation of the monthly mean ozone concentration after corrections for seasonal variations, long-term trends, the QBO and vortex effects, and the associated particle surface area concentration from 1991 to 1994 (Ansmann et al., 1996). The increase in the particle surface area due to Mount Pinatubo is clear associated with this increase in aerosol particles are negative monthly mean deviations in ozone that persist until fall 1993, when the surface area approaches the preeruption values. Similarly, the decrease in the total column ozone from 1980-1982 to 1993 observed at Edmonton, Alberta, Canada, and shown at the beginning of this chapter in Fig. 12.1 has been attributed to the effects of the Mount Pinatubo eruption (Kerr et al., 1993). 

FIGURE 13.9 Trend in column O, (a) from November 1984 to May 1991 based on SAGE II measurements in the stratosphere (at pressures above 82.5 mbar, 0 and dashed lines) and TOMS measurements (solid line) and (b) from January 1988 to May 1991, which was a period of relatively small and stable aerosol particle concentrations. Note change in vertical scale. (Adapted from Cunnold et al., 1996.)... 

Steele, H. M., and R. P. Turco, "Separation of Aerosol and Gas Components in the Halogen Occultation Experiment and the Stratospheric Aerosol and Gas Experiment (SAGE) II Extinction Measurements Implications for SAGE II Ozone Concentrations and Trends, J. Geophys. Res., 102, 19665-19681 (1997b). 

Similar downward trends in PMI() have been observed at surface measuring sites in the United States in urban, suburban, and rural areas. Figure 16.44, for example, shows the trends in the annual average PMI() levels in these three types of air environments (Darlington et al., 1997). Reductions of 3-4% per year have been observed. Simultaneously, the annual average gas-phase concentrations of S02 and NOx, precursors to sulfate and nitrate in particles, decreased. Downward trends of —1.6—1-8% per year in the optically active aerosol over the United States has also been reported (e.g., Hofmann, 1993). 

Several atmospheric aerosol samples were collected in Shanghai and Dalian and PCDD/Fs in total suspended particles were reported (Yang et al., 2004). The mean concentrations of total PCDD/Fs were 55.5 and 19.2 pg m-3, and the mean I-TEQs were 0.928 and 0.334pg m-3, respectively. The predominant congeners were the lower chlorinated congeners. The pollution level is comparable to the general trend of urban industrial sites (0.1-0.4 pg TEQ m-3, Lohmann and Jones, 2000). 

In addition to ice formation, salts also precipitate as these solutions are lofted to higher altitudes. A consequence of the formation of these solid phases (ice and salts) and the low-temperature eutectics of strong acids (Fig. 3.5) is that the atmospheric solutions become more and more acidic with altitude (Fig. 5.8). For example, the final elevation (temperature) examined is 11.54 km (—50 °C). At this point, the calculated concentrations of the Hubbard Brook solution are H+ = 7.55m with acid anions (Cl-, NO3, SO4-, HSOJ) = 7.91m. Similarly, for the Mt. Sonnblick solution, H+ = 6.50 m and acid anions = 6.90 m. These acidic trends are in line with stratospheric chemistries, which are predominantly sulfuric/nitric acid aerosols (Carslaw et al. 1997). For example, the total acid concentration at 20.7km in the stratosphere is 10.17m (calculated from fig. 7 in Carslaw et al. 1997), which is in line with our lower atmospheric concentrations. 

As in the case of mercury, a long-term trend in increasing lead concentration is apparent from an examination of lead aerosols associated with Greenland snow10. ... 

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