Lagrangian methods for climatological analysis of regional atmospheric transport with an emphasis on Texas ozone exceedances

A quantitative climatology of atmospheric transport in Texas is developed using previously described Lagrangian trajectory methods (Rogers and Bowman, 2001; Bowman and Carrie, 2002). The trajectories are computed using winds from 1979-2001 from the National Center for Environmental Prediction (NCEP) Reanalysis Project data set. Probability distributions are created for particle transport using trajectories from urban areas, making six-hourly particle distributions available from four urban areas in Texas. These probability distributions represent a quantitative understanding of regional air transport. Time-dependent Green's functions are calculated given initial conditions such as urban areas weighted with respect to population. The Green's functions describe how air from urban areas is transported through the atmosphere as a function of time. Summertime backward Lagrangian trajectories initialized at 5 Texas Commission on Environmental Quality (TCEQ) monitoring stations are grouped according to the ozone value recorded at the station at the initialization time of the trajectory. The directions of the trajectories in each group are used to determine the relationship between the transport characteristics of the circulation over Texas and regional-scale observations of pollutants. Synoptic conditions occurring at the time of summertime ozone exceedances at the 5 TCEQ stations are investigated in order to resolve what conditions are likely to coincide with ozone exceedances.