Sensitivity of U.S. Surface Ozone Sensitivity of U.S. Surface Ozone toto

Isoprene Emissions & Chemistry:Isoprene Emissions & Chemistry:

An Application of the 1°x1An Application of the 1°x1°° North American NestedNorth American Nested

GEOS-CHEM ModelGEOS-CHEM Model(v. 5-07-08) Arlene Fiore, Larry Horowitz, Drew Purves,

Hiram Levy II, Mathew Evans, Yuxuan Wang, Qinbin Li and Bob Yantosca

GEOS-CHEM MeetingApril 5, 2005

Fiore et al., J. Geophys. Res., in press

GEOS-CHEM 1°x1° Evaluation: July 2001 1-5 p.m. Surface O3 (ppbv)

Mean Bias = 6±7 ppbv; r2 = 0.40

Recent Changes in Biogenic VOC Recent Changes in Biogenic VOC EmissionsEmissions

Isoprene

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

SweetgumInvasion of

Pine plantations

Substantial isoprene increases in southeastern USA largely driven by human land-use decisions

Land-use changes not presently considered in CTMs

Ratio of mid-1990s to mid-1980sisoprene emissions

MOZART-2 … … but not in but not in MOZART-2MOZART-2

Change in July 1-5 p.m. surface O3

Increases in isoprene emissions reduce surface OIncreases in isoprene emissions reduce surface O33 in in Southeastern US in GEOS-CHEM…Southeastern US in GEOS-CHEM…

ppbv

GEOS-CHEM

Little change(NOx-sensitive)

Isoprene nitrates

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

O3 (slower ) Low-NOx, high-isopreneO3

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

O3OH RO2

NO (very fast) NO2

High-NOx

ISOPRENE

Isoprene does react directly with O3 in our SE US GEIA simulation:O3+biogenics (10d) comparable to O3+HOx (16d), O3+h-> OH (11d)

Uncertainty#1

EmissionsUncertainty

#2

?Sink for NOx?

#1: Uncertainty in Surface O#1: Uncertainty in Surface O33 due to Isoprene Chemistry due to Isoprene Chemistry

Change in July mean 1-5 p.m. surface O3 (MOZART-2)

When isoprene nitrates act as a NOx sink

ppbv

GEIA

GEIA: global inventory

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

(1011 molecules isoprene cm-2 s-1)

#2: Uncertainty in Surface O#2: Uncertainty in Surface O3 3 due to Isoprene Emissionsdue to Isoprene Emissions

5.6 Tg C

2.8 Tg C

(ppbv)

Difference in July 1-5 p.m. surface O3 (Purves–GEIA)

July Anthrop. NOx emissions

(1011 molec cm-2 s-1)

Higher isoprenedecreases O3

High-NOx

regime

Ju

ly is

op

ren

e e

mis

sio

ns

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

MOZART-2 shows similar results to GEOS-CHEM if isoprene nitrates are a NOx sink

Revisiting changes in July 1-5 p.m. surface O3 (ppbv) due to isop emis changes from mid-1980s to mid-1990s

From Ugarte et al. (2003)

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

High-NOx

region

• Better constrained isoprene emissions are needed to quantify:1. isoprene contribution to E. U.S. surface O3 2. how O3 responds to both anthrop. and biogenic emission changes (deserves consideration in planning biofuel plantations)

Utility of satellite CH2O columns? New inventories (MEGAN, BEIS-3) more accurate? Constraints from ICARTT observations?

• Recent isoprene increases may have reduced surface O3 in the SE

Does this regime actually exist? Fate of organic nitrates produced during isoprene oxidation?

Conclusions and Remaining Challenges

With PURVES

Vertical slices through 34N: enhanced isoprene, CH2O, PAN at surface & upper trop for GEIA compared to Purves

With GEIA

Insights from NASA INTEX-NA flights over SE US?

0 0.1 .25 0.5 1. 5. .1 .2 .5 1. 3. 5. 0 0.1 .25 0.5 0.8 1.0 0. .05 0.1 0.2 0.5 2.

Longitude

Alt

itu

de

Trends in Anthropogenic Emissions: 1985 to 1995

CO

Large decreases in CO and VOC EmissionsSome local increases in NOx

Higher biogenic VOCs

Net effectOn O3?

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

VOC NOx

Ratio of 1995 to 1985 Emissions

Wit

h G

EIA

Is

op

ren

e E

mis

Wit

h P

urv

es e

t al

.Is

op

ren

e E

mis

With BVOC Changes With Anthrop. Changes

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

changes With Anthrop.+ BVOC Changes

Changes in Anthropogenic NOx emissions dominate O3 responseBut response depends upon choice of isoprene emission inventory

Comparison with observed changes?

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

(1993-1997) – (1983-1987)

Obs: EPA AIRSGEOS-CHEM: GEIA GEOS-CHEM: Purves

Observed changes in O3 are not explained by regional emission changes alone…

Poor correlation (r2 ~ 0) betweenobserved and simulated changes

with anthropogenic + biogenic emissions changes

(ppbv)

°

High-NOx:O3 as isop

Change in July O3 (ppbv; 1-5 p.m.)Isoprene reduced 25% NOx reduced 25%

Low-NOx, high isop:O3 as isop

With GEIA

With Purves

Identify O3 chemistry regime with precursor emissions reductions

July Anthropogenic NOx Emissions

(1011 molec cm-2 s-1)

Choice of isoprene inventory also criticalfor predicting O3 response to changes in isoprene and anthropogenic NOx emissions

stronglyNOx-sensitive

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

GEOS-CHEM base-caseJuly 1-5 p.m. mean

NOx

ISOP

Other model studies indicate SE US is near “maximum VOC capacity point”, beyond which VOCs suppress O3 formation [Kang et al., 2003].

VOC

Ozone NOx-saturated

NOx- sensitive

High-NOxLow-NOx

“isoprene-saturated”??