Changes in Spatial and Temporal Ozone
Patterns Resulting from Emissions
Reductions: Implications for Research
Needs to Support Regulatory Applications
NASA AQAST 6th Biannual Meeting
January 15-17, 2014
Heather Simon
Motivation
• Ozone is an important atmospheric oxidant: changes in spatial and
temporal ozone patterns affect NOx cycling and secondary aerosol
formation
• Changing spatial and temporal patterns will affect overall ozone
exposure to individuals and populations
• To fully evaluate health impacts of ozone it is important to understand
changes in the entire ozone distribution, not just changes in peak
concentrations
• Ozone damage to plants is most reflective of cumulative rather than peak
ozone exposure
• Changing spatial patterns affect how areas will implement controls to
meet air quality goals
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Background
•
Our analysis indicates that regional NOx reductions are the most effective way
to meet the current standard in most cities that are currently violating the ozone
NAAQS
•
To better understand the effects of substantial emissions reductions on spatial
and temporal patterns of ozone, we look at how ozone will change with 50%
and 75% cuts in US Anthropogenic NOx emissions from 2007 levels
•
Model-predicted ozone response to across-the-board cuts in US anthropogenic
NOx was applied to observed ozone concentrations on an hourly basis
•
Using the Higher Order Decoupled Direct Method (HDDM) in the CMAQ model,
we were able to predict nonlinear response and estimate spatial and temporal
patterns of ozone for various NOx cut scenarios
•
Details on methodology available at Simon et al. (2012) ES&T, 47, 2304-2313
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Ozone Responses Analyzed in 15 Study Areas
Detroit
Chicago
Sacramento
Cleveland
Denver
St. Louis
Boston
New York
Philadelphia
Baltimore
Washington, DC
Los Angeles
Atlanta
Dallas
Houston
This talk will focus on select example results from
these cities to demonstrate general patterns
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Summary of Findings
•
•
•
In general we saw that high ozone concentrations decreased and low ozone concentrations
increased in response to NOx emissions cuts
Most high ozone in the U.S. occurs in NOx limited conditions
– Exceptions include some days in Houston and LA
Lowest ozone tends to occur in conditions where available NOx titrates ozone
– Near large sources of NOx emissions where NOx/VOC ratios are high
– At times when ozone production is low/absent
• Nighttime
• Winter
• Cloudy days
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Change in Diurnal Patterns of Ozone
•As a result of NOx reductions:
•Ozone decrease at the high end of distribution (especially during daytime)
•Ozone increases at the low end of distribution(especially at night)
•Interquartile range of ozone concentrations can increase or decrease
depending on location and time of day
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Change in Seasonal Patterns of Ozone
•As a result of NOx reductions:
•Ozone decrease at the high end of distribution (especially during summer)
•Ozone increases at the low end of distribution(especially during winter)
•Interquartile range of ozone concentrations can increase or decrease depending on
location and time of day
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•Higher ozone days shift to earlier in the year
Changes in Spatial Patterns of 4th high Ozone
Philadelphia 3-yr avg of 4th high MDA8:
2006-2008 obs
Chicago 3-yr avg of 4th high MDA8:
2006-2008 obs
Philadelphia with 75% NOx cuts
Chicago with 75% NOx cuts
ppb
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Changes in Spatial Patterns of Seasonal Mean Ozone
Philadelphia Mean May-Sept MDA8:
2006-2008 obs
Chicago Mean May-Sept MDA8:
2006-2008 obs
Dampened
pattern
Philadelphia with 75% NOx cuts
Inverted
pattern
Chicago with 75% NOx cuts
ppb
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What Can Ambient Data Tell Us About
These Trends?
• We have an extensive ground-based ozone monitoring network
with data dating back several decades
• The past 15 years provide a “natural experiment” to look at
ambient ozone trends over a period of dramatically decreasing
NOx emissions
• US NOx emissions dropped from 22.6 million TPY in 2000 to
12.9 million TPY in 2011
• Caution: past trends may not reflect behavior which will occur
from future emissions reductions
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Analysis of Ambient Ozone Trends Shows Spatial and Temporal Changes
Over the Past Decade Qualitatively Similar to Those Predicted by Modeling
Urban Chicago
area trends
MDA8 Ozone (ppb)
MDA8 Ozone (ppb)
MDA8 Ozone (ppb)
Oct-Apr
MDA8 Ozone (ppb)
May-Sep
Rural Chicago
area trends
Year
Interquartile range
5th-95th percentile
Year
Urban monitors = population density > 1000 people/km 2
Rural monitors = population density < 400 people/km 2
Analysis of Ambient Ozone Trends Shows Spatial and Temporal Changes
Over the Past Decade Qualitatively Similar to Those Predicted by Modeling
MDA8 Ozone (ppb)
Rural Philadelphia
area trends
Interquartile range
5th-95th percentile
MDA8 Ozone (ppb)
Oct-Apr
MDA8 Ozone (ppb)
May-Sep
MDA8 Ozone (ppb)
Urban Philadelphia
area trends
Year
Year
Urban monitors = population density > 1000 people/km 2
Rural monitors = population density < 400 people/km 2
What Can the AQAST Community Contribute?
•A key challenge is to tease out effects from NOx changes vs other
factors
•NOx emissions reductions were not uniform in time or space
•Emissions of VOCs also decreased to a lesser extent
•Meteorological variability
•Satellite NO2 measurements provide a good opportunity to correlate
changes in ozone to changes in ambient NO2
•AQAST projects already underway provide a great opportunity for
collaboration and policy-relevant analyses
•Proposed AQAST tiger team project, 2013-2014: Relationships
and trends among satellite NO2 columns, NOx emissions, and air
quality in North America
•Other ideas from the AQAST community are welcome
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Acknowledgements
•
•
•
•
Ben Wells
Adam Reff
Neil Frank
Karen Wesson
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