Atmospheric concentration, variations

Since concentration variations have measurable effects on the cell voltage, a measured voltage cannot be interpreted unless the cell concentrations are specified. Because of this, chemists introduce the idea of standard-state. The standard state for gases is taken as a pressure of one atmosphere at 25°C the standard state for ions is taken as a concentration of 1 M and the standard state of pure substances is taken as the pure substances themselves as they exist at 25°C. The half-cell potential associated with a halfreaction taking place between substances in their standard states is called ° (the superscript zero means standard state). We can rewrite equation (37) to include the specifications of the standard states ... 

The nature and causes of the atmospheric CO2 concentration variations on different time scales are very interesting and only partially understood. The "anthropogenic transient" has been... 

Wallace JC, Hites RA. 1996. Diurnal variations in atmospheric concentrations of poychlorinated biphenyls and endosulfan implications for sampling protocols. Environ Sci Technol 30(2) 444-446. 

The reaction of volatile chlorinated hydrocarbons with hydroxyl radicals is temperature dependent and thus varies with the seasons, although such variation in the atmospheric concentration of trichloroethylene may be minimal because of its brief residence time (EPA 1985c). The degradation products of this reaction include phosgene, dichloroacetyl chloride, and formyl chloride (Atkinson 1985 Gay et al. 1976 Kirchner et al. 1990). Reaction of trichloroethylene with ozone in the atmosphere is too slow to be an effective agent in trichloroethylene removal (Atkinson and Carter 1984). 

The second factor is the temporal variation in concentrations in different ecosystem compartments. For example, sediments and prey fish exhibit less temporal variation in mercuiy concentration than do air or water, and thus statistically valid estimates of their status can be collected with less frequent monitoring (e.g., annual sampling for prey fish vs. daily or hourly sampling for atmospheric concentrations of mercury). 

In calculations two periods were considered—the accumulation time (5 years), during which PCB atmospheric concentration was 1 ng/m3 and the clearance interval with air concentration assumed equal to zero. It was considered that pollutant input to soil takes place only due to gas exchange with the atmosphere. The calculations resulted in the profile of pollutant vertical distribution. This profile allows drawing conclusions about the penetration depth variation. 

No large variation in sampling rates is observed among the different studies, despite differences in exposure conditions, such as wind speeds, temperature, and SPMD mounting layout. It should be noted, however, that the effect of temperature is partially accounted for by our use of temperature-corrected log A oa values. An example of the application of Eq. 3.68 for calculating atmospheric concentrations is given in Box 3.3. 

Figure 2 indicates Mn/Fe to be somewhat above the crustal ratio through 19 March, and thereafter a marked Increase is seen. The aerosol ratio Zn/Fe averages about 20 times greater than in the earth crust (somewhat greater on 20-21 March), showing "anomalous" atmospheric enrichment of Zn first recognized by Rahn (7). Since particle size distribution measurements, discussed below, show substantial fine particle concentrations of both Zn and Mn, the processes for their transfer to the atmosphere must be different from those for the other six elements of Figure 2. However, their concentration variations in time still resemble those of Fe shown in Figure 1 and therefore these elements may also be relatively large scale characteristics of air masses, in contrast to S where regional pollution sources and aerosol formation processes must be Important.

Shepson, P. B D. R. Hastie, H. I. Schiff, M. Polizzi, J. W. Botten-heim, K. Anlauf, G. I. Mackay, and D. R. Karecki, Atmospheric Concentrations and Temporal Variations of Cj-C, Carbonyl Compounds at Two Rural Sites in Central Ontario, Atmos. Environ., 25A, 2001-2015 (1991). 

The factors that influence the chemical resolution of sensors are well understood and are not discussed here. This section reviews the factors that control the temporal resolution of sensors to be used for eddy correlation. In the analysis of the design of chemical sensors to be used for eddy correlation it is instructive to consider the different components of chemical sensor systems separately to determine the influences that they have on the temporal response to variations in the atmospheric concentration of a trace constituent. Of course this analysis is an oversimplification because the total systems operate in a more complex fashion, but it is a useful exercise. 

The size distribution of air particles not only influences the distribution and partitioning dynamics of POPs, but also determines dry and wet deposition flux of POPs. An interesting phenomenon was observed for relationship among atmospheric PAHs, particle size distribution, and the levels of PAHs in soil (Kim, 2004). For urban sites, the composition pattern and absolute concentrations of PAHs in soil were well correlated with those in air where the atmospheric particles size was distributed evenly among seasons with predominant amount of fine particles < 3 pm. Dry deposition flux of PAHs followed seasonal variation in atmospheric concentration in urban site. However, at a suburban site with large seasonal variation in particle size distribution, dry deposition flux and soil residue did not reflect the seasonal variation of atmospheric PAHs. From this result, site-specificity in atmospheric particle distribution may also influence the distribution and residues in the underlying soil. 

Yeo, H.-G., Choi, M., Sunwoo, Y., 2004b. Seasonal variations in atmospheric concentrations of organochlorine pesticides in urban and rural areas of Korea. Atmos. Environ. 38, 4779 1788. 

Figure 4. Variations of atmospheric concentrations of trace elements in the gas and particulate phase observed during a continuous two-month sampling period.

The critical need to achieve high signal-to-noise ratios for spatially resolved measurement of several free radicals has spawned a number of research efforts aimed at improving our ability to observe such radicals as OH, HO2, NO, NO2, etc., with orders of magnitude better sensitivity than was previously available. A major impetus behind this research has been the realization that atmospheric variability on the spatial scale of a hundred meters in the vertical drives fluctuations in several of the key reactiye species, which provide ample concentration variation to carry out covariance studies to establish cause and effect within subsets of free radical reaction sets. 

Pearson, J.E. and Moses, H., 1966. Atmospheric radon-222 concentration variation with height and time. J. Appl. Meteorol., 5 175-181. 

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