# Presentation: 306744

## Background Ozone in Surface Air

**Background Ozone in Surface Air**
**over the United States:**
**Variability, Climate Linkages, **
**and Policy Implications **

**Arlene M. Fiore **
**  ****Department of Atmospheric and Oceanic Sciences Seminar**
**University of Wisconsin-Madison**
**December 6, 2004**

## Acknowledgments

**Daniel Jacob**
**Brendan Field**
**Hongyu Liu ****	**
**Bob Yantosca**
**Qinbin Li ****	**
**Duncan Fairlie ****	**

**David Streets**
**Suneeta Fernandes**

**Carey Jang**
**Jason West ****	**

## What is the origin of tropospheric ozone? 

**NO****x**
**VOC**

**NO****x**
**VOC**

**CONTINENT 2 **

**OCEAN**

**O****3**

**Boundary layer**
**     ****(0-3 km)**

**Free Troposphere**

**CONTINENT 1 **

**What is the origin of tropospheric ozone? **

**OH**

**HO****2**

**VOC, CH****4****, CO**

**NO**

**NO****2**

**h******

**O****3**

**O****3**

**Hemispheric Pollution**

**Direct Intercontinental Transport**

**air pollution (smog)**

**air pollution (smog)**

**    **

**Stratospheric O****3**

**Stratosphere**

**~12 km**

## Number of People Living in U.S. Counties Violating National Ambient Air Quality Standards (NAAQS) in 2001

**Number of People Living in U.S. Counties Violating National Ambient Air Quality Standards (NAAQS) in 2001**

**EPA [2002]**

**124 ppbv: 40.2**

**84 ppbv: 110.3**

**Carbon monoxide (CO)**

**Lead**

**Nitrogen **
**dioxide**

**Ozone (O****3****)**

**Particles < 10 ********m (PM****10****)**

**Particles < 2.5 ********m (PM****2.5****)**

**Sulfur dioxide**
**(SO****2****)**

**Any pollutant**

**Millions of People**

**0**

**0.007**

**11.1**

**0.7**

**72.7**

**2.7**

**133.1**

**0**

**0**

**50**

**100**

**150**

## The Risk Increment Above the Background is Considered when setting the NAAQS for Ozone

**Environmental risk**

**Ozone**
**Concentration**

**Background**

**NAAQS**

**Acceptable**
**added**
**risk**

**Need a quantitative estimate for background ozone**
** **
**EPA chose a constant value (40 ppbv) in previous        ****	****review of O****3**** standard **

## Range of “background O3” estimates in U.S. surface air

**Range of “background O****3****” estimates in U.S. surface air**

**20**

**40**

**60**

**80**

**100**

**O****3**** (ppbv)**

**Range considered **
**by EPA during last **
**revision of O****3**** standard**

**84 ppbv: threshold for**
**current U.S. O****3 ****standard**

## “REGULATORY BACKGROUND OZONE” DEFINITION: Ozone concentrations that would exist in the absence of anthropogenic emissions from North America [EPA, 2003]

**  ****Fires**

**Land**
**biosphere**

**Human**
**activity**

**Ocean**

** ****NORTH AMERICA**

**Lightning**

**“****Background” air**

**X**

**Outside natural**
**influences**

**Long-range transport**
**of pollution**

**“****REGULATORY BACKGROUND OZONE” DEFINITION:**** ****Ozone concentrations that would exist in the absence of ****anthropogenic emissions from North America [*****EPA*****, 2003]**

**stratosphere**

**lightning**

## Intercontinental Transport of Pollution at Northern Midlatitudes

**Reduced Visibility from Transpacific Transport of Asian Dust**

**O****3**

**Glen Canyon, Arizona**

**Contributes to Hemispheric Background O****3**

## EPA-Defined Background is Not Directly Observable  Must be Estimated with Models

**Hemispheric Pollution   =   ****Background**** – ****Natural O****3**** level**

**EPA-Defined Background is ****N****ot Directly**** ****Observable ******** Must be Estimated ****with**** Models**

**Standard simulation****.....2x2.5 GEOS-CHEM, ****compare ****	****	****	****	****	****with observations **
**Background****..................no anthrop. NO****x****, CO, NMVOC ****	****	****	****	****	****emissions from N. America **
**Natural O****3**** level****.............no anthrop. NO****x****, CO, NMVOC ****	****	****	****	****	****emissions globally; CH****4**** = 700 ppbv**
**Stratospheric****................tagged O****3**** tracer simulation **

**Simulations for Ozone Source Attribution: Mar-Oct 2001**

_**TOOL:**_** ****	****GEOS-CHEM 3D**** ****Tropospheric Chemistry ****Model**** ****	****[*****Bey et al.,***** 2001] (uses assimilated meteorology; **
**	****48 ********; 4****o****x5o or 2ox2.5o horiz. resn., 24 tracers)**

## 2001 CASTNet Stations (EPA, Nat’l Park Service)

**X Elevated sites (> 1.5 km)**
**    ****Low-lying sites **

_**APPROACH:**_** ****Use ****2001 CASTNet data**** in conjunction with ****GEOS-CHEM ****to**
**	****1.  quantify background O****3**** and its various sources**
**	****2.  diagnose origin of springtime high-O****3**** events at **
**	****     ****remote U.S. sites, previously attributed to natural, **
**                  ****stratospheric influence**

## Case Study: Voyageurs National Park, Minnesota(May-June 2001)

**CASTNet observations**
**Model**
**Background**
**Natural O****3**** level**
**Stratospheric**

**+**

*****

**Hemispheric**
**pollution**

**Regional**
**pollution**

**}**

****

**}**

****

**Background: 15-36 ppbv**
**Natural level: 9-23 ppbv**
**Stratosphere: < 7 ppbv**

*Lefohn et al.* [2001] suggest a stratospheric
- source as the likely origin of high-O3 events
- frequently observed in June

**X**

## Case Study: Yellowstone NP, Wyoming(March-May 2001) 

**CASTNet observations**
**Model**
**Background**
**Natural O****3**** level**
**Stratospheric**

**+**

*****

**Hemispheric**
**pollution**

**Regional**
**pollution**

**}**

****

**}**

****

**Background at high-altitude site (2.5 km) not necessarily representative of background contribution at low-lying sites**

- Frequent high-O3 events previously
- attributed to natural, stratospheric source [*Lefohn et al.,* 2001]

**X**

## *

**Model**
**Background**
**Natural O****3**** level**
**Stratospheric**

**+**

*****

**Ozone (ppbv)**

**Days in March 2001**

**Southeast (<1.5 km)**

**West (>1.5 km)**

**Background O****3**** **
**higher at high-altitude western sites **

**Background O****3**
**lower at low-lying**
**southeastern sites; **
**decreases with **
**highest observed O****3**** **

**X**

## Background O3 even lower under polluted conditions

**Background on polluted days well below 40 ppbv assumed by EPA **
****** ****health risks underestimated with current approach**

**Ozone (ppbv)**

**Cumulative Probability**

**Regional**
**Pollution**

**Daily mean afternoon O****3**** at 58 U.S. CASTNet sites **

**June-July-August**

## Monthly mean afternoon (1-5 p.m.) surface O3 

**Monthly mean afternoon (1-5 p.m.) surface O****3**** **

**{**

**{**

**{**

**{**

**Hemispheric pollution**
**enhancement**
**(5-12 ppbv)**

**Mean background: 20-35 ppbv**
**Mean natural level: 13-27 ppbv**
**Mean stratosphere: 2-7 ppbv**

**Regional pollution**
**from N. Am. emis.**
**(8-30 ppbv)**

**Background O****3**** varies with season**

## Daily afternoon (1-5 p.m.) surface O3 March-October 2001 

**Daily afternoon (1-5 p.m.) surface O****3 ****March-October 2001 **

**Background  15-35 ppbv; ****Natural 10-25 ppbv; ****Stratosphere < 20 ppbv**

**Probability ppbv****-1**

**Typical ozone values in U.S. surface air:**

**Compiling results from all CASTNet sites... **

**CASTNet sites**

**Model at CASTNet**

**Stratospheric**

**Natural**

**Background**

##  Climate Linkage

**High-O****3**** events at remote U.S. sites in spring can be explained largely by pollution from North America**
**Hemispheric pollution enhances U.S. background**

**CONCLUSIONS ...**

**and their implications for public policy**

******health risk from O****3**** underestimated in present EPA risk assessments**

******these events do not represent U.S. background conditions and **
**    ****should not be used to challenge legitimacy of O****3 ****NAAQS**

**international agreements to reduce hemispheric background should **
**   ****improve air quality & facilitate compliance w/ more stringent standards**

****** ****Climate Linkage**

## Air quality-Climate Linkage:CH4, O3 are important greenhouse gasesCH4 contributes to background O3 in surface air

**NO****x**
**NMVOCs**

**NO****x**
**NMVOCs**

**CONTINENT 2 **

**OCEAN**

**O****3**

**Boundary layer**
**     ****(0-3 km)**

**Free Troposphere**

**CONTINENT 1 **

**Air quality-Climate Linkage:****CH****4****, O****3**** are important greenhouse gases****CH****4**** contributes to background O****3**** ****in surface air**

**OH**

**HO****2**

**VOC,**** ****CH****4****, CO**

**NO**

**NO****2**

**h******

**O****3**

**O****3**

**Global Background O****3**
**(Hemispheric Pollution)**

**Direct Intercontinental Transport**

**greenhouse gas**

**air pollution (smog)**

**air pollution (smog)**

## More than half of global methane emissions 

**More than half of global methane emissions **
**are influenced by human activities**

**ANIMALS**
**90**

**LANDFILLS**
**50**

**GAS**
**60**

**COAL**
**40**

**RICE**
**85**

**TERMITES**
**25**

**WETLANDS**
**180**

**BIOMASS**
**BURNING**
**20**

**GLOBAL METHANE**
**SOURCES (Tg CH****4**** yr****-1****) **

## Radiative Forcing of Climate, 1750-Present:Important Contributions from Methane and Ozone 

**IPCC [2001]**

**Level of scientific understanding**

## Impacts of future changes in global anthropogenic emissions on climate 

**Impacts of future changes in global anthropogenic ****emissions on climate **

**50% **
**anthr.**
** ****NO****x**

**2030 **
** ****A1**

** ****50% **
**anthr.**
** ****CH****4**

**50% **
**anthr.**
**NMVOC**

**2030 **
** ****B1**

| IPCC scenario | Anthrop. NOx emissions
  (2030 vs. present)
   Global              U.S. |  | Methane emissions
(2030 vs. present) |
| --- | --- | --- | --- |
| A1 | +80% | -20% | +30% |
| B1 | -5% | -50% | +12% |

**Change in radiative forcing (W m****-2****) relative to 1995 base case**

***Fiore et al., GRL, 2002***

## Methane emission controls reduce surface O3 everywhere

**from 50% reductions in global anthropogenic CH****4**** emissions**

**Methane emission controls reduce surface O****3 ****everywhere**

## Methane emission reductions shift entire summer afternoon surface O3 frequency distribution over U.S. 

**Methane emission reductions shift entire summer afternoon surface O****3**** frequency distribution over U.S. **

**Probability ppbv****-1**

**Ozone Concentration (ppbv****)**

## Impacts of future changes in global anthrop. emis. on U.S. air quality: 

**Impacts of future changes in global anthrop. emis. on U.S. air quality:**** **

**1995**
**(base)**

**50% **
**anthr.**
**VOC**

**50% **
**anthr.**
**CH****4**

**50% **
**anthr.**
**NO****x**

**2030 **
**A1**

**Increase in U.S. **
**pollution events **
**despite domestic**
**decline in anthrop.**
**emissions **

**Number of summer grid-square days with O****3**** > 80 ppbv**

**2030 **
**B1**

| IPCC 2030
scenario | Anthrop. NOx emissions
Global              U.S. |  | Methane emissions |
| --- | --- | --- | --- |
| A1 | +80% | -20% | +30% |
| B1 | -5% | -50% | +12% |

## Rising emissions from developing countries lengthen the O3 pollution season in the United States

**Rising emissions from developing countries lengthen the O****3**** pollution season in the United States**

**2030 A1**

**1995 Base Case**

**Degradation of U.S. **
**air quality from rise **
**in global emissions **
**despite domestic **
**reductions **

## Background O3 is typically less than 40 ppbv; even lower under polluted conditions 

**High-O****3**** events at remote U.S. sites in spring can be explained largely by pollution from North America**
**Hemispheric pollution enhances U.S. background**

**CONCLUSIONS,**

**Public policy implications, ****and Next steps**

******health risk from O****3**** underestimated in present EPA risk assessments**

******these events do not represent U.S. background conditions and **
**    ****should not be used to challenge legitimacy of O****3 ****NAAQS**

**international agreements to reduce hemispheric background should **
**   ****improve air quality & facilitate compliance w/ more stringent standards**

**compare additional model estimates of background (MOZART-2) for**
**    ****use in risk assessments **

**feasibility of methane control [*****West and Fiore*****, submitted; AGU poster]**
**better characterize relationship between methane sources and surface **
**    ****ozone response**

** ****extend source attribution for background **