NASA AQAST 6th Biannual MeetingJanuary 15-17, 2014

Heather Simon

Changes in Spatial and Temporal Ozone Patterns Resulting from Emissions

Reductions: Implications for Research Needs to Support Regulatory Applications

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

2

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, 2304-23133

4

Ozone Responses Analyzed in 15 Study Areas

Baltimore

Boston

Los Angeles

Denver

Philadelphia

Atlanta

ChicagoCleveland

Dallas

Detroit

Houston

New York

Sacramento

St. Louis Washington, DC

This talk will focus on select example results from these cities to demonstrate general patterns

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

5

6

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

7

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• Higher ozone days shift to earlier in the year

8

Changes in Spatial Patterns of 4th high Ozone Chicago 3-yr avg of 4th high MDA8:

2006-2008 obsPhiladelphia 3-yr avg of 4th high MDA8:

2006-2008 obs

Chicago with 75% NOx cutsPhiladelphia with 75% NOx cuts

ppb

9

Changes in Spatial Patterns of Seasonal Mean Ozone Chicago Mean May-Sept MDA8:

2006-2008 obsPhiladelphia Mean May-Sept MDA8:

2006-2008 obs

Chicago with 75% NOx cutsPhiladelphia with 75% NOx cuts

Inverted patternDampened

pattern

ppb

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

10

Analysis of Ambient Ozone Trends Shows Spatial and Temporal Changes Over the Past Decade Qualitatively Similar to Those Predicted by Modeling

Interquartile range5th-95th percentileOct-Apr

May-Sep

Urban Chicago area trends

Rural Chicago area trends

Urban monitors = population density > 1000 people/km2

Rural monitors = population density < 400 people/km2

MD

A8

Ozo

ne (p

pb)

MD

A8

Ozo

ne (p

pb)

MD

A8

Ozo

ne (p

pb)

MD

A8

Ozo

ne (p

pb)

Year Year

Interquartile range5th-95th percentile

Oct-Apr

May-Sep

Urban Philadelphia area trends

Rural Philadelphia area trends

Urban monitors = population density > 1000 people/km2

Rural monitors = population density < 400 people/km2

MD

A8

Ozo

ne (p

pb)

MD

A8

Ozo

ne (p

pb)

MD

A8

Ozo

ne (p

pb)

MD

A8

Ozo

ne (p

pb)

Year Year

Analysis of Ambient Ozone Trends Shows Spatial and Temporal Changes Over the Past Decade Qualitatively Similar to Those Predicted by Modeling

What Can the AQAST Community Contribute?

13

• 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

Acknowledgements

• Ben Wells• Adam Reff• Neil Frank• Karen Wesson

14