World Meteorological Day

We hope you like math, because to commemorate World Meteorological Day, we asked our resident meteorologist Dave K. to give us a brief overview of air modeling and dispersion and how it impacts air quality.

To acquire an air permit authorization in Texas (and other states) to construct and operate an industrial facility, such as a high production rock crushing plant that produces more than 250 tons per hour, the owner/operator of the equipment is required to conduct an air dispersion modeling analysis. 

Simply speaking, air dispersion modeling is a computerized system, based on a mathematical algorithm (see Figure 1) that simulates air flow, in which the output creates a prediction of pollutant (such as particulate matter) concentrations in ambient air near the surface, where humans breath in the air. 

Figure 1.  The simplified Gaussian air dispersion model.

There are several inputs into the modeling system. However, for the purpose of brevity, this summary only describes the meteorological data component of the plume being dispersed. Of this input component, simplifying down to two of the most important meteorological factors is useful: (1) wind speed and (2) wind direction (refer to Figure 2) that occur in any one given location.

Figure 2.  Impacts associated with wind speed and wind direction.

As the ambient wind speed increases, the concentration of the pollutant will decrease (for example, a strong pressure gradient associated with an approaching cold front); and vice versa, as the wind speed decreases, the concentration of the pollutant will increase (for example, nighttime calm conditions or strong high-pressure centers).

When there is a consistent wind direction (for example, southerly flow from the Gulf of Mexico over several days), the flow of pollutant maintains impact over the same area causing concentrations to increase.  However, if the wind direction is varying and changing every day (for example, a cold or warm front passing through frontal passages), then the flow of pollutants is spread out (dispersed) and impacts occur across a larger area causing concentrations to decrease.

Nothing is stagnate in meteorology--as wind speed and wind direction can change daily and by location, so does the quality of the air we breathe. #worldmetday