Pesticide Residues in the Atmosphere - Pesticides: Evaluation of Environmental Pollution - page 207

• Macroscale (spatial scale larger than 1000 km or temporal scales ranging from a
few days to months). Atmospheric movements are associated with inhomogene-
ities of the surface energy balance at the Earth (global or synoptic) scale. In these
scales, the hydrostatic approach is assumable (neglecting vertical air movements
and favoring horizontal advections). Studies on the long-range transport (LRT) of
atmospheric pollutants are framed in this scale.
• Mesoscale (spatial scales between 1 and 1000 km or temporal scales ranging from
one hour to a few days). On this meteorological scale, the atmospheric flows
are driven by the hydrodynamic processes (as, e.g., channeling through valleys,
surface roughness effects, compensatory subsidences, etc.) and also by the inho-
mogeneities of the surface energy balance (mainly due to spatial variations in
features such as the physiographic properties of the ground, land use, water
availability, slope, and orientation of terrain). From the atmospheric pollutant
point of view, thermodynamic effects are the most relevant ones, because they
drive the boundary layer dynamics under low synoptic forcing (i.e., under poor
ventilating conditions). The hydrostatic approach is no longer valid in these
scales. Mesoscale meteorological models (nonhydrostatic models) must be able
to reproduce the local circulations, such as breeze or/and upslope circulations.
Studies on medium- and short-range transport of atmospheric pollutants are
framed in this scale.
• Microscale (spatial scales under 1 km or temporal scales ranging from a few hours
to seconds). On this meteorological scale, air flow is strongly determined by sur-
face features such as geometry of buildings, their orientation with respect to the
average wind direction, etc. Wind flows are generated as the result of both thermal
effects and hydrodynamic effects (channeling, roughness effects, etc.). Studies on
the short-range transport of atmospheric pollutants are framed in this scale.
7.3 Entry of Pesticides into the Atmosphere
The highest pesticide concentrations are usually found near the application area and near
the moment of the application. Nevertheless, pesticides can be found far away from the
application site (e.g., Unsworth et al. 1999; Coscollà et al. 2010) and at other times of the year
after the application (e.g., Scheyer et al. 2007a,b).
There are several ways in which pesticides can enter the atmosphere:
• Due to the drift after application
• Due to volatilization from the soil
• Due to volatilization from the leaves
• From suspended particulate matter from wind erosion
• Due to losses during the application
• From evaporation in the surface water
Figure 7.1 shows a general scheme of the different ways in which pesticides enter, dis-
perse, and interact in the environment. Atmospheric compartment, on which this chapter
is focused, is presented in a more detailed way.