A Model-to-Monitor Evaluation of 2011 National-Scale Air Toxics Assessment (NATA).

Zhuqing Xue,Chunrong Jia

doi:10.3390/toxics7010013

Abstract

Environmental research has widely utilized the ambient concentrations of hazardous air pollutants (HAPs) modeled by the National-Scale Air Toxics Assessment (NATA) program; however, limited studies have evaluated the model’s performance. This study aims to evaluate the model-to-monitor agreement of the 2011 NATA data with the monitoring data reported to the U.S. Environmental Protection Agency’s (EPA) Air Quality System (AQS). Concentrations of 27 representative HAPs measured at 274 sites in the U.S. in 2011 were merged with NATA data by census tract. The comparison consisted of two steps for each HAP: first, the model-monitor difference at each site was compared with the limit of quantitation (LOQ); second, the modeled annual average was compared to the 95% confidence interval of the monitored annual average. Nationally, NATA could predict national medians of most HAPs well; however, it was unable to capture high concentrations. At individual sites, a large portion of model-monitor differences was below the LOQs, indicating they were unquantifiable. Model-to-monitor agreement displayed inconsistent patterns in terms of chemical groups or EPA regions and was strongly impacted by the comparison methods. The substantial non-agreements of NATA predictions with monitoring data require caution in environmental epidemiology and justice studies that are based on NATA data.

Highlights

Valid and representative data of hazardous air pollutants (HAPs) are required to evaluate emission compliance, air quality attainment, and population health risks
Environmental Protection Agency (EPA) has been working with state, local and tribal air pollution control agencies to measure ambient HAP concentrations
We calculated the 95% confidence interval (CI) of the annual mean concentration of a compound, and determine if the single National-Scale Air Toxics Assessment (NATA) annual average value fell within this 95% CI

Summary

Introduction

Valid and representative data of hazardous air pollutants (HAPs) are required to evaluate emission compliance, air quality attainment, and population health risks. Agency (EPA) aimed to reduce HAP emissions by 75% of the 1993 level to meet the requirements of the Government Performance and Results Act. EPA has been working with state, local and tribal air pollution control agencies to measure ambient HAP concentrations. The current monitoring efforts are inadequate for increasingly refined health and climate studies. Health data are collected at the individual level or small geographic scale; sparsely distributed air monitoring stations often lack spatial representativeness [10]. The sub-kilometer scale variation of air pollutants requires dense sampling networks with more than 1–2 nodes per km2 [13], which far exceed the current capacity. Modeling programs are developed to estimate exposures at high temporal and spatial resolutions [14]

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