Seasonal concentration variations

In summary, a number of chemical constituents in polar snow and ice have seasonal concentration variations that make them suitable for dating ice cores by counting annual layers. In... 

The ground-level air concentrations of 7Be and 137Cs at 46 °N and 71 °N are shown in Figure 8. The 137Cs concentration variations are typical of relatively long lived nuclear weapons-produced radionuclides and illustrate the variation in the concentrations of these radionuclides with latitude and time. It is evident that the concentrations and seasonal concentration variations were substantially different at the two latitudes. There also were differences in the seasonal variations between 7Be and the bomb-produced radionuclides. Based on the idealized curves drawn... 

The behavior of MTBE through the different environmental compartments has been investigated using various modelling approaches. For example, the EU risk assessment used the simplest type of fugacity models (a Level 1 model) and concluded that from diffuse sources 93.9% of MTBE is in the air phase, 6.0% in the water phase, and 0.05% in the soil phase [2]. However, another study by Environment Canada for Southern Ontario [61] used the Level III model and predicted 56% of MTBE in the air, 42% in surface water, and 0.5% in soil and sediment. As can be observed, models developed so far differed in their predictions of relative MTBE concentrations for relevant environmental compartments and of seasonal concentration variations further, they have hardly considered the formation of transformation products [62]. Moreover, limitations in pollutant environmental data or key physicochemical parameters often make it difficult to validate model predictions. 

Several studies have reported daily and seasonal variations in raw water arsenic concentration. For example, one study reported diurnal variations in arsenic of 39-59 and 57-83 p,g/L in a stream (16). Seasonal concentration variations have also been reported (17-20), including 11-21 (21) and 16-63 p,g/L (22) in surface waters and 10-220 pg/L (23) in a groundwater. Variations in arsenic concentration and speciation will become increasingly important to water utilities trying to meet a lowered MCL. 

Metal hydroxides (e.g., Fe, Mn, Al) can also be a problem (Rauten-bach and Albrecht, Membrane Processes, Wiley, New York, 1989). A chemical analysis of the feed solution composition along with consideration of solubility products allows one to determine the significance of precipitation. Solubility products can be affected by temperature, pH, and ionic strength. Seasonal temperature variations must be considered. Concentrations of silica need to be < 120 mg/L in the feed. 

Aquifers which are closely connected to a river (as for the case of Groundwater System S) may be influenced by abrupt input variations that are driven by the corresponding concentration changes in the river. In order to analyze the resulting concentrations in the aquifer, the solution of the transport equation (Eq. 25-10) will be discussed for different time-dependent input concentrations at x = 0, Cin(t). In the river typical time scales of change are of the order of minutes (in case of an accidental spill) to days, but seasonal variations also exist for some chemicals. In contrast, transport within the aquifer is slower than most riverine concentration variations. The question arises how the river dynamics are transmitted to the groundwater. Three different cases are discussed ... 

Fig. 4 Key features of submicron aerosol measured at North European EUSAAR stations, (a) location of the stations, (b) histograms of the annual N30 5o concentrations, (c) seasonal median size distributions, and (d) seasonal N10o variation at Hyytiala, Finland...

The two EUSAAR/ACTRIS stations in the Britain and Irish stations show not only a significant inter-station variability, but also many similarities. The stations have high seasonal variation and large variance in intra-seasonal concentrations. The station data show a prominent spring-summer maximum in all sizes from 30 to 70 nm. The variability was probably due to occurrences of both clean Atlantic and polluted local air masses, and the maximum value at Mace Head during summer months can be attributed to enchanted marine biota activity, which increases the sub-micron particle mass concentration of non-seasalt sulfate and organic aerosol [21],... 

Concentrations of contaminants in the atmosphere may vary significantly from time to time due to seasonal climatic variation, atmospheric turbulence, and velocity and direction of wind. The most important meteorological factors are (1) wind conditions and the gustiness of wind, (2) the humidity and precipitation, (3) the temperature, which varies with latitude and altitude, (4) barometric pressure (varying with the height above the ground), and (5) solar radiation and the hours of sunshine, which vary with the season. 

One possible reason for seasonal arsenic concentration variations is uptake and release of arsenic by aquatic river plants. These plants may absorb arsenic in the spring and summer (28,29), causing a very slight decrease in arsenic concentra-... 

Seasonal variation and horizontal distribution of nutrients N, P, and Si DIN (the sum of nitrate, nitrite, and ammonium) and phosphate concentrations did not have an obvious annual, less than annual, or even seasonal cyclical variation. Throughout Jiaozhou Bay in one year, the DIN values were >2.36 pmol/L and the phosphate values were >0.16 pmol/L. Silicate seasonal variation showed a repeated annual cyclic pattern. Every year there was only one highest value of silicate concentration in surmner. Throughout Jiaozhou Bay, silicate values were <2 pmol/L in spring, autumn, and winter, but in summer were >2 pmol/L. For example, at stations 1 and 4 in Jiaozhou Bay, the seasonal variations of DIN concentration, phosphate concentration and silicate concentration were as shown in Figs. 3.60, 3.61, and 3.62. 

The seasonal amphtude (ratio between summer and winter concentration) represents a measure for aimual photochemical ozone production (neglecting the first possible ozone sinks). Before the 1950s, seasonal ozone variation was small. Considering the O3 concentration as an expression for the source-sink budget, even the summer-winter ratio must be a sensible parameter, but this also depends on altitude, showing a characteristic increase with height. 

The first graph (Ref 1) illustrates the season ll variation of CO concentration and the steady increase over the last 50 years. The second graph (Ref 4) summarizes the growth in global emissions of COj into the atmosphere as a result of burning of fossil fuels. 

The properties of a botanical gum are determined by its source, the climate, season of harvest, and extraction and purification procedures. Table 6 illustrates one of the important basic properties of all gums, ie, the relationship between concentration and solution viscosity. The considerable viscosity variation observed among gums from different sources determines, in part, their uses. 

Unesterified tocopherols are found in a variety of foods however, concentration and isomer distribution of tocopherols vary gready with source. Typically, meat, fish, and dairy contain <40 mg/100 g of total tocopherols. Almost all (>75%) of this is a-tocopherol for most sources in this group. The variation in the content of meat and dairy products can be related to the content of the food ingested by the animal. A strong seasonal variation can also be observed. Vegetable oils contain significant levels of y-, P-, and 5-tocopherol, along with a-tocopherol (Table 3). 

Fig. 4-3. Seasonal variation of suspended particulate matter concentration. Composite of 20 nonurban sites. United States. Source Pirtas, R., and Levin, H. ]. Air PoUut. Control Assoc. 21(6), 329-333, 1971.

The oxygen atom produced in this step can react with oxygen molecules to produce more ozone, and so the ozone concentration in the stratosphere normally remains constant, with seasonal variations. Because the decomposition of ozone... 

The models also assume a steady-state condition which suggests that the carbon cycle is structured, stable, and balanced and will remain so indefinitely. This mechanistic view of biogeochemistry allows for little variation even though it is known that fluctuations and variation occur seasonally. The concentration of... 

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