# Presentation: 051950

## Recent Changes in Eastern U.S. Forests: Implications for Air Quality 

**Recent Changes in Eastern U.S. Forests: Implications for Air Quality **

**Arlene M. Fiore **

**Seminar at the **
**Center for Sustainability and the Global Environment (SAGE) **
**University of Wisconsin-Madison**
**December 8, 2004**

## Acknowledgments

**Mat Evans**
**Qinbin Li      **
**Bob Yantosca**
**Yuxuan Wang**

**Drew Purves**
**Steve Pacala**

**Larry Horowitz**
**Chip Levy**

## O3

**ISOPRENE**

**+****     NO****x**** ****	******

**Isoprene Emissions are generally thought to contribute to O****3**** production over the eastern United States ****[*****e.g.Trainer et al*****., 1987; *****NRC***** 1991]**

**Vegetation changes ******** Impact on O****3****?****	**
**-- Climate**
**-- Land-use****	**

**+**

**air pollution (smog)**
**Harmful to health,**
**vegetation**

**O****3**

**O****3**** formation in eastern U.S. is typically **
**more responsive to controls on anthrop. **
**NO****x**** emissions than anthrop. VOCs**

**(VOC)**

## Future scenario for conversion of agricultural lands to poplar plantations for biofuels

**Future scenario for conversion of agricultural lands to poplar plantations for biofuels**

*from D. Purves*

**Poplars are high-isoprene emitting trees**
****** ****land-use decisions have implications for air quality**

## 7.1 Tg C 

**GEIA: Global Isoprene Emission Inventory****  **

**7.1 Tg C**** **

**2.6 Tg C**** **

**[10****12**** atom C cm****-2**** s****-1****]**

**Isoprene emissions – July 1996**

**[from Paul Palmer]**

**Isoprene Emission Inventories****uncertain by at least a factor of 2**

**BEIS2: Regional Isoprene Emission Inventory****  **

**... ****and there is new evidence for decadal changes**

## Purves et al. [2004]: observation-based biogenic VOC (BVOC) emission estimates for mid-1980s and mid-1990s

- Plot

- Tree

- Leaf area

- Environment of leaves (temp, light)

- Emission rate

- Minimal complexity approach
- Empirical rather than mechanistic / physiological
- Based on USDA **F**orest **I**nventory **A**nalysis data
- Emission estimates for isoprene and monoterpenes

***Purves et al*****. [2004]: observation-based biogenic VOC (BVOC) emission estimates for mid-1980s and mid-1990s**

*from D. Purves*

## from D. Purves

**Purves Base isoprene inventory similar to BEIS2**

**Species,**
**Stem diameter (1985, 1995)**
**Fate (lived, died, harvested)**

*from D. Purves*

***Purves et al*****. [2004]: observation-based BVOC ****emission estimates for mid-1980s and mid-1990s**

**280,000 Re-surveyed plots,**
**2.7 million trees in FIA in eastern U.S.**

## Recent Changes in Biogenic VOC Emissions

**Recent Changes in Biogenic VOC Emissions**

**Isoprene**

**Monoterpenes**

**[*****Purves et al*****., *****Global Change Biology*****, 2004]**

**Trends in anthropogenic precursors?**

****** ****Substantial isoprene increases in southeastern USA**
**     ****largely driven by human land-use decisions**
****** ****Land-use changes not presently considered in CTMs**

## Trends in Anthropogenic Emissions: 1985 to 1995

**Trends in Anthropogenic Emissions: 1985 to 1995**

**CO**

**VOC**

**NO****x**

**Large decreases in CO and VOC Emissions**
**Some local increases in NO****x**
**Higher biogenic VOCs**

**Net effect**
**On O****3****? **

**from US EPA national emissions inventory database****(http://www.epa.gov/air/data/neidb.html)**

## GEOS-CHEM

**GEIA**

***Purves***

**(10****11**** molecules isoprene cm****-2**** s****-1****)**

**GEOS-CHEM**

**MOZART-2**

**Quantify O****3**** response to **
**reported biogenic and**
**anthropogenic emissions **
**changes**

_**Approach**_**:  Insights from two chemical transport models **

**1. Test whether results are**
**model-dependent**

**2. Determine sensitivity to **
**uncertainties in isoprene **
**emissions **

**2. Determine sensitivity to **
**uncertainties in isoprene-**
**NO****x****-O****3**** chemistry **

**July mean isoprene emissions**

- Isoprene + NOx may lock up NOx (as isoprene nitrates), suppressing O3 formation
- Assumed in GEOS-CHEM but not in MOZART-2

## Tool #1:  GEOS-CHEM tropospheric chemistry model [Bey et al., 2001]

- Uses assimilated meteorology: GEOS-3 1°x1° fields for 2001
- 48 vertical levels ( 9 below 2 km)
- Regridded to 4°x5° for global spinup and boundary conditions for **nested 1°x1° over North America** [*Wang et al*., 2004; *Li et al*., 2004]
- 31 tracers; NOx-CO-hydrocarbon-O3 chemistry coupled to aerosols
- GEIA isoprene emission algorithms [*Guenther et al*., 1995]
- v. 5-07-08 (http://www-as.harvard.edu/chemistry/trop/geos/index.html)

**July 2001 1-5 p.m. Surface O****3 ****(ppbv)**

## GEOS-CHEM Evaluation: July 2001 1-5 p.m. Surface O3 (ppbv)

**Mean Bias = 6±7 ppbv; r****2 ****= 0.40**

## +

**GEOS-CHEM July 1-5 p.m. O****3**

**Isoprene emission changes from**
**mid-80s to mid-90s [*****Purves et al*****., 2004]**

**+**

**Complicated Chemistry... **

**Change in July 1-5 p.m. **
**surface O****3**

**Increases in isoprene emissions reduce surface O****3**** in Southeastern US**

**ppbv**

## Complications to Chemistry: Isoprene may also decrease surface O3 			                 in low-NOx, high isoprene settings

**Complications to Chemistry: Isoprene may also decrease surface O****3 ****	****	****	****                 ****in low-NO****x****, high isoprene settings**

**Thought to occur in pre-industrial [*****Mickley et al*****., 2001];**
**and present-day tropical regions [*****von Kuhlmann et al*****., 2004]**

**Isoprene does react directly with O****3**** in our SE US GEIA simulation:**
**O****3****+biogenics (10d) comparable to O****3****+HO****x ****(16d), O****3****+h********-> OH (11d)**

## Increasing Isoprene Decreases O3 in Low-NOx, High-isoprene regions

**GEOS-CHEM base-case**
**July 1-5 p.m. mean **

**NO****x**

**ISOP**

**“****isoprene-saturated”??**

## Choice of isoprene inventory critical for predicting base-case O3 

**GEIA**

**GEIA: global inventory**

***Purves et al., *****[2004] (based on FIA data; similar to BEIS-2)**

**(10****11**** molecules isoprene cm****-2**** s****-1****)**

**Choice**** ****of isoprene inventory critical for predicting base-case O****3**** **

**5.6 Tg C**

**2.8 Tg C**

**“****isoprene-**
**saturated”**

**High-NO****x**
**regime**

**July isoprene emissions**

## Identify O3 chemistry regime with precursor emissions reductions 

**°**

**High-NO****x****:**
**O****3 ****  as isop**

**Change in July O****3**** (ppbv; 1-5 p.m.)**

**Isoprene reduced 25% **

**NO****x**** reduced 25%**

**Low-NO****x****, high isop:**
**O****3****   as isop**

**With GEIA**

**With Purves**

**Identify O****3**** chemistry regime with precursor emissions reductions **

**July Anthropogenic **
**NO****x**** Emissions**

**(10****11**** molec cm****-2**** s****-1****)**

**Choice of isoprene **
**inventory also critical**
**for predicting O****3**** **
**response to changes **
**in isoprene and **
**anthropogenic NO****x**** **
**emissions**

**strongly**
**NO****x****-sensitive**

## Change in Mean July Surface O3 (ppbv; 1-5 p.m.) reflecting 1980s to 1990s emissions changes 

**Isoprene Emis**

**With Purves et al.**
**Isoprene Emis**

**With BVOC Changes**

**With Anthrop. Changes**

**Change in Mean July Surface O****3**** (ppbv; 1-5 p.m.) reflecting 1980s to 1990s emissions changes**

**With Anthrop.+ BVOC Changes**

**Changes in Anthropogenic NO****x**** emissions dominate O****3**** response**
**But response depends upon choice of isoprene emission inventory**

**Comparison with observed changes? Impact on high-O****3**** events?**

## Model vs. Obs.: Change in July O3 1980s to 1990s (ppbv; 1-5 p.m.)

**Model vs. Obs.: Change in July O****3**** 1980s to 1990s (ppbv; 1-5 p.m.)**

**(1993-1997) – (1983-1987)**

**Obs: EPA AIRS**

**GEOS-CHEM: GEIA**

**GEOS-CHEM: Purves**

**Observed changes in O****3**** are not explained **
**by regional emission changes alone...**

**Poor correlation (r****2**** ~ 0) between**
**observed and simulated changes**

** **
** ****dominated by anthrop.**
**(NO****x****) emissions but**
**BVOC changes may offset **
**for most extreme events   **

**Impact of Sensitivity Simulations on High-O****3**** Events:**

** **
** ****decrease with isoprene**
**except for GEIA SE**

** ****decrease with NO****x****, **
**larger response with GEIA**

**Unclear whether recent**
**BVOC emission changes mitigated/exacerbated high-O****3**** events**

## Does MOZART-2 also predict decreases in O3 resulting from increases in isoprene emissions?

**Isoprene emission changes from**
**mid-80s to mid-90s [*****Purves et al*****., 2004]**

**Does MOZART-2 also predict decreases in O****3**** resulting from increases in isoprene emissions?**

**Little change**
**(NO****x****-sensitive)**

**Isoprene nitrates are not a NO****x**** sink in MOZART-2: O****3**** Sensitivity?**

## Change in July mean 1-5 p.m. 

**Change in July mean 1-5 p.m. **
**surface O****3  ****when isoprene **
**nitrates act as a NO****x**** sink**
****** ****6-12 ppbv impact!**

**What is the O****3**** sensitivity to the uncertain fate of **
**organic isoprene nitrates?**

**Revisit O****3**** response to isoprene changes with this assumption**

## Understanding fate of isop. nitrates essential for predicting sign of response to changes in 

**(due to isop emis changes from mid-1980s to mid-1990s)**

**Chemical uncertainty: MOZART-2 shows similar results to GEOS-CHEM ****if isoprene nitrates are a NO****x**** sink**

**Understanding fate of isop. nitrates essential for predicting sign of response to changes in **
**	****isoprene emissions**

**With 12% yield of isoprene nitrates**

**GEOS-CHEM: GEIA **

**GEOS-CHEM: Purves **

**MOZART-2: GEIA **

**ppbv**

## Conclusions and Remaining Challenges

**Better constrained isoprene emissions are needed to quantify:**
**isoprene contribution to E. U.S. surface O****3**** **
**how O****3**** responds to both anthrop. and biogenic emission changes**
**      ****(deserves consideration in planning biofuel plantations)**
**Utility of satellite CH****2****O columns? **
**New inventories (MEGAN, BEIS-3) more accurate?**
**Aircraft observations from recent ICARTT campaign?**
**Recent isoprene increases may have reduced surface O****3**** in the SE**
**Does this regime actually exist? **
**Fate of organic nitrates produced during isoprene oxidation?**
**Results consistent in MOZART-2 and GEOS-CHEM**
**Reported regional emission changes from 1980s to 1990s alone do not explain observed O****3**** trends**
**Are anthropogenic emissions inventories sufficient to support trend studies? (*****Parrish et al*****., *****JGR***** 2002)**
**Decadal shifts in meteorology?**
******   ****Changing global O****3**** background?**

**Conclusions and Remaining Challenges**