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. 2016 Sep;124(9):1443-52.
doi: 10.1289/EHP190. Epub 2016 May 6.

Assessing Temporal and Spatial Patterns of Observed and Predicted Ozone in Multiple Urban Areas

Heather Simon  1 , Benjamin Wells, Kirk R Baker, Bryan Hubbell
Affiliations

Assessing Temporal and Spatial Patterns of Observed and Predicted Ozone in Multiple Urban Areas

Heather Simon et al. Environ Health Perspect. 2016 Sep.

Abstract

Background: Ambient monitoring data show spatial gradients in ozone (O3) across urban areas. Nitrogen oxide (NOx) emissions reductions will likely alter these gradients. Epidemiological studies often use exposure surrogates that may not fully account for the impacts of spatially and temporally changing concentrations on population exposure.

Objectives: We examined the impact of large NOx decreases on spatial and temporal O3 patterns and the implications on exposure.

Methods: We used a photochemical model to estimate O3 response to large NOx reductions. We derived time series of 2006-2008 O3 concentrations consistent with 50% and 75% NOx emissions reduction scenarios in three urban areas (Atlanta, Philadelphia, and Chicago) at each monitor location and spatially interpolated O3 to census-tract centroids.

Results: We predicted that low O3 concentrations would increase and high O3 concentrations would decrease in response to NOx reductions within an urban area. O3 increases occurred across larger areas for the seasonal mean metric than for the regulatory metric (annual 4th highest daily 8-hr maximum) and were located only in urban core areas. O3 always decreased outside the urban core (e.g., at locations of maximum local ozone concentration) for both metrics and decreased within the urban core in some instances. NOx reductions led to more uniform spatial gradients and diurnal and seasonal patterns and caused seasonal peaks in midrange O3 concentrations to shift from midsummer to earlier in the year.

Conclusions: These changes have implications for how O3 exposure may change in response to NOx reductions and are informative for the design of future epidemiology studies and risk assessments.

Citation: Simon H, Wells B, Baker KR, Hubbell B. 2016. Assessing temporal and spatial patterns of observed and predicted ozone in multiple urban areas. Environ Health Perspect 124:1443-1452; http://dx.doi.org/10.1289/EHP190.

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Conflict of interest statement

Although this paper has been reviewed by the U.S. EPA and approved for publication, it does not necessarily reflect the U.S. EPA’s policies or views. The authors declare they have no actual or potential competing financial interests.

Figures

Figure 1
Figure 1
Maps showing the 2006–2008 average annual 4th-highest maximum daily 8-hr average ozone (MDA8 O3), the regulatory metric (parts per billion; top panels), and May–September mean MDA8 O3 (parts per billion; bottom panels) values in Atlanta for observed conditions (left panels), and predicted changes with 50% U.S. nitrogen oxide (NOx) emissions reductions (center panels) and 75% U.S. NOx emissions reductions (right panels). Colored squares show locations of monitoring sites, and colored dots show interpolated values at census-tract centroids.
Figure 2
Figure 2
Maps showing the 2006–2008 average annual 4th-highest maximum daily 8-hr average ozone (MDA8 O3), the regulatory metric, (parts per billion; top panels) and May–September mean MDA8 O3 (parts per billion; bottom panels) values in Philadelphia for observed conditions (left panels), and predicted changes with 50% U.S. nitrogen oxide (NOx) emissions reductions (center panels) and 75% U.S. NOx emissions reductions (right panels). Colored squares show locations of monitoring sites, and colored dots show interpolated values at census-tract centroids.
Figure 3
Figure 3
Maps showing the 2006–2008 average annual 4th-highest maximum daily 8-hr average ozone (MDA8 O3), the regulatory metric, (parts per billion; top panels) and May–September mean MDA8 O3 (parts per billion; bottom panels) values in Chicago for observed conditions (left panels), and predicted changes with 50% U.S. nitrogen oxide (NOx) emissions reductions (center panels) and 75% U.S. NOx emissions reductions (right panels). Colored squares show locations of monitoring sites, and colored dots show interpolated values at census-tract centroids.
Figure 4
Figure 4
Histograms showing population living in Atlanta locations with various 2006–2008 average 4th-highest maximum daily 8-hr average ozone (MDA8 O3) (top panels; parts per billion) and May–September mean MDA8 O3 (bottom panels; parts per billion), for observed conditions (left panels), and predicted changes resulting from 50% U.S. nitrogen oxide (NOx) emissions reductions (center panels) and 75% U.S. NOx reductions (right panels). Colors show the breakdown of each histogram by population density.
Figure 5
Figure 5
Histograms showing population living in Philadelphia locations with various 2006–2008 average 4th-highest maximum daily 8-hr average ozone (MDA8 O3) (top panels; parts per billion) and May–September mean MDA8 O3 (bottom panels; parts per billion), for observed conditions (left panels), and predicted changes resulting from 50% U.S. nitrogen oxide (NOx) emissions reductions (center panels) and 75% U.S. NOx reductions (right panels). Colors show the breakdown of each histogram by population density.
Figure 6
Figure 6
Histograms showing population living in Chicago locations with various 2006–2008 average 4th-highest maximum daily 8-hr average ozone (MDA8 O3) (top panels; parts per billion) and May–September mean MDA8 O3 (bottom panels; parts per billion), for observed conditions (left panels), and predicted changes resulting from 50% U.S. nitrogen oxide (NOx) emissions reductions (center panels) and 75% U.S. NOx emissions reductions (right panels). Colors show the breakdown of each histogram by population density.
Figure 7
Figure 7
Histograms showing population living in Chicago locations with various 2006–2008 average 4th-highest maximum daily 8-hr average ozone (MDA8 O3) (top panels; parts per billion) and May–September mean MDA8 O3 (bottom panels; parts per billion), for observed conditions (left panels), and predicted changes resulting from 50% U.S. nitrogen oxide/volatile organic compound (NOx/VOC) emissions reductions (center panels) and 75% U.S. NOx/VOC emissions reductions (right panels). Colors show the breakdown of each histogram by population density.
Figure 8
Figure 8
Distribution of 8-hr daily maximum ozone (O3) concentrations in Philadelphia by month at an urban (left panels) and a rural (right panels) monitoring site. Top plots show the interquartile range (25th to 75th percentile values) across all days in each month. Bottom plots show minimum and maximum values across all days in each month.
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