LETTER pubs.acs.org/est
Comment on “Do Some NOx Emissions Have Negative Environmental Damages? Evidence and Implications for Policy” n their Viewpoint titled “Do Some NOx Emissions Have Negative Environmental Damages? Evidence and Implications for Policy”,3 the authors represent as novel the finding in two studies that marginal reductions in NOx emissions from particular sources in certain areas may increase PM2.5 levels and yield negative health impacts. The authors then entreat the EPA to “commission a review of these studies”, to be evaluated by the EPA Science Advisory Board and submitted as a report to Congress. We argue that the Viewpoint in general, and these recommendations in particular, incompletely consider atmospheric science and do not account for current best practices in air quality management. PM2.5 formation is governed by complex nonlinear chemistry, and so the impact of reducing precursor emissions differ across receptors for three reasons: (1) levels of SO2, NOx, NH3; (2) meteorology (particularly temperature and relative humidity); and, (3) availability of ozone and related oxidants (e.g., OH, H2O2, etc.). Transient spatial and temporal increases in PM2.5 from decreases in NOx emissions are well documented in literature.1,4 Under certain atmospheric conditions, a reduction in NOx (particularly near-surface mobile NOx emissions under cold climate conditions) sometimes leads to increases in ozone and result in localized increases in PM2.5 concentrations, though this depends on baseline levels of NOx and VOC.1,4,5 For this reason, reductions of NOx within NOx-rich urban city centers (e.g., Chicago) may lead to localized increases in PM2.5 levels and may increase population exposure to PM2.5, thus resulting in the disbenefit reported in Fann et al.2 Photochemical models used by EPA and State air agencies account for these nonlinear effects. While there is clear policy relevance to the negative benefit per ton estimates reported in Fann et al.2 and elsewhere, this effect should be considered within the broader context of air quality management policy. In its 2004 report on air quality management in the U.S., the National Academies noted that air quality
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attainment strategies should balance emission reductions across multiple pollutant precursors and spatial scales6. To this end, benefit per ton estimates may inform the development of specific control strategies that aim to maximize human health benefits while achieving air quality targets. Indeed, EPA recently completed a pilot project for the city of Detroit, in which it employed a risk-based and multiple pollutant approach to air quality management.2,7 This strategy weighed local and regional emission reductions among a variety of sources and across several PM2.5 and ozone precursors, and toxic air pollutants, to design an implementation plan that maximized human health benefits and achieved a more equitable distribution of risk. Rather than reacting to incomplete evidence, approaches to air quality management such as these illustrate an approach to attainment plans that accounts for all of the best available science. Neal L. Fann* Air Quality Analysis Division, U.S. Environmental Protection Agency, Mail Drop C539-07 109 T.W. Alexander Drive Durham, North Carolina 27711, United States
Dr. Sharon B. Phillips
(2) Fann, N.; Fulcher, C. M.; Hubbell, B. J. The influence of location, source, and emission type in estimates of the human health benefits of reducing a ton of air pollution. Air Qual. Atmos. Health 2009, 2 (3), 169–176. (3) Fraas, A.; Lutter, R. Do some NOx emissions have negative environmental damages? Evidence and implications for policy. Environ. Sci. Technol. 2011, 45 (18), 7613– 7614. (4) Myslieiec, M. J.; Kleeman, M. J. Source apportionment of secondary airborne particulate matter in a polluted atmosphere. Envrion Sci. Technol. 2002, 36 (24), 5376–5384. (5) Pun, B. K.; Seigneur, C.; Bailey, E. M.; Gautney, L. L.; Douglas, S. G.; Haney, J. L.; Kumar, N. Response of atmospheric particulate matter to changes in precursor emissions: A comparison of three air quality models. Envrion Sci. Technol. 2008, 42 (3), 831–837. (6) U.S. National Research Council (NRC). Air Quality Management in the United States; National Academies: Washington, DC, 2004. (7) Wesson, K.; Fann, N.; Morris, M.; Fox, T.; Hubbell, B. A multipollutant, risk-based approach to air quality management: case study for Detroit. Atmos. Pollut. Res. 2010, 1, 296–304. (8) Fann, N.; Roman, H. A.; Fulcher, C. M.; Gentile, M. A.; Hubbell, B. J.; Wesson, K.; Levy, J. I. Maximizing health benefits and minimizing inequality: incorporating local-scale data in the design and evaluation of air quality policies. Risk Analysis 2011, 6 (31), 908–922.
Air Quality Analysis Division, U.S. Environmental Protection Agency
Dr. Carey Jang Air Quality Analysis Division, U.S. Environmental Protection Agency
Dr. Farhan H. Akhtar Health and Environmental Impacts Division, U.S. Environmental Protection Agency
’ AUTHOR INFORMATION Corresponding Author
*Phone: (919) 541-0209; fax: (919) 5415315; e-mail:
[email protected].
’ REFERENCES (1) Ansari, A. S.; Pandis, S. P. Response of inorganic PM to precursor concentrations. Envrion Sci. Technol. 1998, 32 (18), 2706–2714.
This article not subject to U.S. Copyright. Published 2011 by the American Chemical Society
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Received: October 19, 2011 Accepted: October 24, 2011 Published: November 11, 2011
dx.doi.org/10.1021/es203710m | Environ. Sci. Technol. 2011, 45, 10290–10290
