# Presentation: 306745

## Linking regional air pollution with 

**global chemistry and climate: **
**The role of background ozone**

**Arlene M. Fiore**
**Adviser: Daniel J. Jacob**

**April 22, 2002**

## Tropospheric ozone links air pollution & climate change (1) primary constituent of smog in surface air [NRC, 1991] (2) 3rd most important greenhouse gas [IPCC, 2001]

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

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

**CONTINENT 2 **

**OCEAN**

**O****3**

**Boundary layer**
**     ****(0-2.5 km)**

**Free Troposphere**

**CONTINENT 1 **

**Tropospheric ozone links air pollution & climate change**** (1) primary constituent of smog in surface air [*****NRC*****, 1991] ****(2) 3****rd**** most important greenhouse gas [*****IPCC*****, 2001]**

**OH**

**HO****2**

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

**NO**

**NO****2**

**h******

**O****3**

**O****3**

**Hemispheric Pollution**

**Direct Intercontinental Transport**

**greenhouse gas**

**air pollution (smog)**

**air pollution (smog)**

## Ozone abatement strategies evolve as our understanding of the O3 problem improves

**1950s**

**Present**

**1980s**

**NMVOCs**

**+ NO****x**

** ****+ CH****4****??**

**Ozone abatement strategies evolve as our understanding of the O****3**** problem improves**

**Abatement**** ****Strategy:**

**O****3**** smog recognized**
**as an URBAN problem:****Los Angeles,**
**Haagen-Smit identifies**
**chemical mechanism**

**Smog considered**
**REGIONAL problem; **
**role of biogenic **
**VOCs discovered**

**A GLOBAL perspective:**
**role of intercontinental**
**transport, background**** **

## Historical and recent evidence suggest that human activities are increasing the hemispheric O3 background

**Cumulative Probability**

**8-h daily maximum ozone probability **
**distribution at rural U.S. sites**
**[*****Lin et al*****., 2000]        **

**1980-1984**

**1994-1998**

**1980-1984**

**1994-1998**

**Ozone (ppbv)**

**Ozone trend at European mountain sites, 1870-1990 [*****Marenco et al*****., 1994]**

**~ 3 ppbv increase over**
**past 20 years**

**~ 5-fold increase over**
**past century**

## Need to quantify U.S. background O3 in surface air for current review of National Ambient Air Quality Standard for O3 (NAAQS)

**What background concentrations should be used to assess the human health risk associated with exposure to O****3****?**
**Is the present (or more stringent future) NAAQS **** ****too close to background concentrations?**

**“****REGULATORY BACKGROUND” DEFINITION: **
**Ozone concentrations that would exist in the absence of anthrop. emissions from North America [*****EPA*****, 2003]**
**25-45 ppbv [*****EPA*****, 1996]**

## An approach for estimating O3 background from observations

**Intercept **
**30 ppb**
**background**
**(clean air)**

**(Pollution coordinate)**

**U.S. Ozone Standard**

**(Index of Aged Pollution)**

**Ozone (ppbv)**

**NOy-NOx (ppbv)**

**Summer 1995 1- 5 p.m. observations at **
**Harvard Forest [*****Munger et al*****., 1996, 1998]**

**Range of background that was  **
**considered for revised O****3**** standard**

- Frequently observed surface O3 concentrations attributed
- to natural  background by
*Lefohn et al.* [2001]

**An approach for estimating O****3**** background from observations**

**background**
**presently used in EPA risk assessments**

## Assess whether GEOS-CHEM is a suitable tool for quantifying the O3 background over the U.S. 	 
	-- Standard statistical metrics + EOF analysis

2. Quantify background contribution to average vs. polluted days  

3. Identify origin of background and variability of its sources 

4. Diagnose source of high-O3 events at remote U.S. sites in spring	
5. Determine combined air quality and climatic implications of various O3 control strategies

		-- Sensitivity simulations & tagged tracers in GEOS-CHEM

**	****-- Standard statistical metrics + EOF analysis**
**2. Quantify background contribution to average vs. polluted days  **
** ****	**
**3. Identify origin of background and variability of its sources **
**	**
**4. Diagnose source of high-O****3**** events at remote U.S. sites in spring****	**
**5. Determine combined air quality and climatic implications of various O****3**** control strategies**
**	****	****-- Sensitivity simulations & tagged tracers in GEOS-CHEM**

_**TOOL:**_** ****	****GEOS-CHEM 3D Tropospheric Chemistry ****Model ****[*****Bey et al.,***** 2001]**
**	****(uses assim. met.; 20-30 ********; 4****o****x5o or 2ox2.5o horiz. resn., 24 tracers)**** **

_**QUESTION:**_** What role does background O****3**** play in linking regional air**
**	****	****quality with global chemistry & climate? **

_**RESEARCH OBJECTIVES:**_

## Summer 1995 afternoon (1-5 p.m.) ozonein surface air over the United States

**Summer 1995 afternoon (1-5 p.m.) ozone****in surface air over the United States**

**AIRS**
**Observations**

**GEOS-CHEM 2ox2.5****o**
**r = 0.66, bias=5 ppbv**
**(for 4****o****x5o resolution **
**r = 0.84, bias=2 ppbv) **

**Notes:**
Broad overview here of model evaluation – will present more detailed comparisons later in the talk with science results
Explain SE overestimate

## EOF ANALYSIS: Characterize spatiotemporal variability of surface O3(daily 1-5 p.m. mean concentrations in summer 1995 over eastern U.S.)  

**EOF ANALYSIS: Characterize spatiotemporal variability of surface O****3****(daily 1-5 p.m. mean concentrations in summer 1995 over eastern U.S.)****  **

**OBS (AIRS)**

**MAQSIP (36 km****2****) **

**r****2**** = 0.60**
**Slope = 0.9**

**r****2**** = 0.57**
**Slope = 0.8**

**r****2**** = 0.68**
**Slope = 0.7**

**East-west**
**EOF**

**Midwest-**
**Northeast**
**EOF**

**r****2**** = 0.86**
**Slope = 1.0**

**r****2**** = 0.76**
**Slope = 1.0**

**r****2**** = 0.80**
**Slope = 1.0**

**Southeast**
**EOF**

## Same fundamental, synoptic-scale processes modulate observed O3 variability at scale of global model horizontal resolution 

**East-west**
**EOF**

**Midwest-**
**Northeast**
**EOF**

**Southeast**
**EOF**

**OBS (AIRS)**

**GEOS-CHEM 2°x2.5°**

**r****2**** = 0.74**
**Slope = 1.2**

**r****2**** = 0.27**
**Slope = 1.0**

**r****2**** = 0.90**
**Slope = 1.0**

**r****2**** = 0.68**
**Slope = 1.0**

**r****2**** = 0.54**
**Slope = 0.8**

**r****2**** = 0.78**
**Slope = 1.0**

## Mean Afternoon Surface Ozone Background (ppbv) in GEOS-CHEM model, Summer 1995

**Background is tagged as ozone produced outside the **
**N. American boundary layer (surface-700 hPa)**

**What is the contribution of the background to pollution episodes?**

**Notes:**
Note: although not using EPA background definition here, consistent results – will switch to later.

## Ozone Background is depleted during regional pollution episodes(due to deposition and chemical loss under stagnant conditions)

**Ozone Background is depleted during regional pollution episodes****(due to deposition and chemical loss under stagnant conditions)**

**Daily mean afternoon O****3**** vs. (NO****y****-NO****x****) At Harvard Forest, MA**** **

**Index of Aged Pollution**

**Background**
**(clean conditions)**

**Background in model**
**(pollution episode)**

**Total Surface Ozone **
**in Model**

**Ozone (ppbv)**

**Background O****3****: **
**produced outside **
**the N. American**
**boundary layer **
**(surface-700 hPa)**

**Observations**

**U.S. Ozone **
**Standard**

## Frequency Distribution of Afternoon Background Ozone Concentrations in U.S. Surface Air Summer 1995 (GEOS-CHEM model)summer ensemble vs. pollution events

**Frequency Distribution of Afternoon Background Ozone Concentrations in U.S. Surface Air ****Summer 1995 (GEOS-CHEM model)****summer ensemble**** vs. ****pollution events**

**Convection upwind**
**occasionally results in**
**high background during**
**pollution events**

**Background Ozone Concentration (ppbv)**

**Probability**

## Range of Asian/European Pollution Surface Ozone Enhancements Over the U.S. in summeras determined from a simulation without these emissions (4°x5°)

**Max Asian/European pollution enhancements**
**(up to 14 ppbv) occur at intermediate ozone levels (50-70 ppbv)**

**MAJOR CONCERN**
**IF OZONE STANDARD**
**WERE TO DECREASE****!**

**tropical **
**air**

**Subsidence of Asian pollution**
**+ local production**

**stagnation**

## Sensitivity Simulations for source attribution Mar-Oct 2001

**Standard simulation****.....2x2.5 GEOS-CHEM, 48 sigma levels**
**	****	****	****2001**
**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 **

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

**Note: Background in the following results is as defined by EPA**

**Use 2001 CASTNet data in conjunction with GEOS-CHEM to**
**investigate how background O****3**** varies with season and region**

## 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)**

**Mar-Oct 2001 U.S. daily **
**mean afternoon surface O****3**

**Background  < 50 ppbv**
**Natural level  < 40 ppbv**
**Stratosphere < 20 ppbv**

## High-O3 “Haywood County” event in North Carolina 

**High-O****3**** “Haywood County” event in North Carolina**** **

**Regional pollution largely controls high-O****3**** events in spring;**
**Model explains these events without a large stratospheric influence**

**Hemispheric**
**pollution**

**Regional**
**pollution**

**}**

****

**}**

****

**APR-MAY 2001 **

**Yellowstone NP, Wyoming**
**March-May 2001**

**Time series at CASTNet sites where high-O****3**** events in spring were previously attributed to stratospheric origin on basis of back-trajectories**

**  ****APR-MAY 2000**

## Ozone (ppbv)

**Ozone (ppbv)**

**Days in March 2001**

**Southeast**

**West**

**Background **
**increases**
**with highest **
**observed O****3**** at **
**western sites **
**in March **

**Background **
**decreases**
**with highest **
**observed O****3**** **
**at SE sites**
**in March **

## Background O3 for risk assessment =f (season, altitude, total O3 concentration)

**Using average background for **
**pollution episodes underestimates **
**risk to human health!**

**Enhancement from N. Amer & hemis. pollution for **
**high O****3 ****concentrations**

**Lower background;**
**larger pollution influence**
**in summer (& fall)**

**Lower background at surface sites;**
**Maximum contribution at the center **
**of the O****3 ****distribution**

**12 elevated**
**sites; **
**all in west**

**58 surface**
**sites**

- Cumulative Probability (daily mean afternoon O3)

**Regional**
**Pollution**

## Air Quality-Climate Linkage:  Impacts of future changes in global anthropogenic emissions (GEOS-CHEM; 4°x5°) 

**50% **
**anth.**
** ****NO****x**

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

** ****50% **
**anth.**
** ****CH****4**

**50% **
**anth.**
**VOC**

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

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

**50% **
**anth.**
**VOC**

**50% **
**anth.**
**CH****4**

**50% **
**anth.**
**NO****x**

**2030 **
**A1**

**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% |

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

**Radiative Forcing* (W m****-2****)**

**CH****4**** links air quality **
**& climate via **
**background O****3**

## 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 **

## Global models can adequately simulate the synoptic conditions important for resolving background and high-O3 conditions

2.  Background O3 varies with season, site elevation, and total surface O3 concentrations
	-- highest at high-altitude western U.S. sites in spring
	-- lower at surface sites and in summer
	-- depleted during polluted conditions 
health risk from O3 underestimated in present EPA risk assessments

3.  High-O3 events at remote U.S. sites in spring previously attributed to a natural stratospheric source are explained largely by regional pollution
these events should not be used to challenge legitimacy of O3 NAAQS

4.  Hemispheric pollution enhances U.S. background; may rise in future 
	international agreements to reduce hemispheric background would improve U.S. air quality & facilitate compliance w/ more stringent standards

5.  Methane emission controls decrease hemispheric background & greenhouse warming
 co-benefits for air quality & climate change mitigation objectives 

**2.  Background O****3**** varies with season, site elevation, and total surface O****3**** concentrations**
**	****-- highest at high-altitude western U.S. sites in spring**
**	****-- lower at surface sites and in summer**
**	****-- depleted during polluted conditions **
**health risk from O****3 ****underestimated in present EPA risk assessments**
**3.  High-O****3**** events at remote U.S. sites in spring previously attributed to a natural stratospheric source are explained largely by regional pollution**
**these events should not be used to challenge legitimacy of O****3**** NAAQS**
**4.  Hemispheric pollution enhances U.S. background; may rise in future **
******	****international agreements to reduce hemispheric background would improve U.S. air quality & facilitate compliance w/ more stringent standards**
**5.  Methane emission controls decrease hemispheric background & greenhouse warming**
****** ****co-benefits for air quality & climate change mitigation objectives **

_**CONCLUSIONS **_**and their implications for policy**