STI analysts perform comparisons of emissions and air quality data as a top-down quality check of emission inventories. We have found this procedure, which we term “emissions reconciliation”, to be a useful means to identify inaccuracies in emission inventories. Emissions reconciliation is performed by selecting appropriate temporal and spatial “slices” of an emission inventory for comparison to ambient air quality measurements. The selections are made on the basis of observed meteorological conditions and the geographic locations of ambient monitoring stations. Comparisons are made by using ratios of pollutants (e.g., hydrocarbons to nitrogen oxides), which helps to account for atmospheric mixing and dilution. Thus, ambient pollutant ratios are compared to inventory pollutant ratios to determine whether the inventory reflects real-world conditions with reasonable accuracy. STI has applied these techniques for several projects, described below.
STI staff analyzed ozone, ozone precursor, and meteorological data collected during the 1995 NARSTO-Northeast Study. We validated and analyzed hydrocarbon and carbonyl data from 13 Photochemical Assessment Monitoring Stations (PAMS) and nine special research sites. We performed an emission inventory reconciliation for three PAMS sites and performed analyses of pollutant transport and mixing height structure, evolution, and effects on ozone concentrations in the Northeast. This work was performed for the Coordinating Research Council.
STI staff analyzed ozone, ozone precursors, and surface and upper-air meteorological data collected during the 1997 Southern California Ozone Study. We validated and analyzed hydrocarbon and upper-air meteorological data, made recommendations to improve Photochemical Assessment Monitoring Stations operations, determined transport patterns, and evaluated the emission inventory. In addition, we produced hourly three-dimensional wind fields using the CALMET diagnostic wind model driven by surface wind data from 244 sites and mixing height and upper-air wind and temperature data collected by 26 radar wind profilers, 6 sodars, and rawinsondes. Mixing height data were derived from Radio Acoustic Sounding System (RASS) virtual temperature (Tv) data coupled with surface Tv, radar profiler reflectivity, and lidar ozone data. Using the results of the wind field analysis, STI staff produced transport trajectories and analyzed the wind fields, trajectories, and mixing height information to explain the spatial and temporal characteristics of ozone and its precursors.
STI staff analyzed upper-air meteorological measurements, the emission inventory, and ozone and precursor trends using Photochemical Assessment Monitoring Stations (PAMS) data collected in the Sacramento, San Joaquin Valley, South Coast, and Ventura Districts. This work was performed for the U.S. EPA.
STI staff critically examined the particulate matter emission inventory for the San Joaquin Valley Air Basin of central California based on the air quality data collected for the Integrated Monitoring Study - 1995 (IMS-95). Differences between expected and observed pollutant distributions indicated areas of the inventory in need of future research. This work was performed as part of the California Regional PM10/PM2.5 Air Quality Study (CRPAQS).
STI staff evaluated the consistency of the emission inventory for the Coastal Oxidant Assessment for Southeast Texas (COAST) photochemical modeling domain with ambient air quality data collected during the 1993 COAST field study. In addition, we used trajectory analysis to examine the evolution of chemical concentrations in air masses over time, evaluated the adequacy of an observation-based algorithm for characterizing conditions of NOx limitations, and considered the implications of the presence of point, area, and mobile sources of NOx along the trajectories.
STI staff assisted the California Air Resources Board in assessing whether adjustments were necessary for the emission inventories of the SARMAP domain, which covers much of central California. We examined VOC emission adjustment factors for regions outside California including the southern Lake Michigan area, the southern United States, and the Texas Gulf Coast. Work conducted in California's South Coast Air Basin was considered and comparisons were made with factors estimated for central California.