QUESTIONS

1. Is hexane more or less reactive with OH than propane?

2. Is pentene or isoprene more reactive with OH?

LARGE SUPPLY OF BIOGENIC VOCs – unrecognized until the 1990s

Isoprene (biogenic VOC)Anthropogenic VOCs

Jacob et al., [1993]

Switches polluted areas in U.S. from NOx-saturated to NOx-limited regime!recognized in Revised Clean Air Act of 1999

Isoprene (C5H8) and monoterpenes (C10H16) are oxidized by OH, O3 and NO3

(generally analogous to alkene rxn) secondary organic aerosol (SOA)

LATEST INVENTORIES OF BIOGENIC vs. ANTHROPOGENIC VOCs

Millet et al. [2007]

…notice difference in scale!

GLOBAL DISTRIBUTION OF ISOPRENE EMISSIONS

MEGAN biogenic emission model (Guenther et al., 2006)

E = f (T, h)

CONSTRAINT ON VOC EMISSIONS FROM SPACE OBSERVATIONS OF FORMALDEHYDE

-0.5

0

0.5

1

1.5

2

2.5x1016

moleculescm-2

SouthAtlanticAnomaly(disregard)

detectionlimit

GOME satellite observations (July 1996)

High values are associated with biogenic emissions (eastern US), anthropogenic emissions (China), fires (Africa, Siberia)

SIMULATED SENSITIVITY OF SURFACE OZONETO EMISSION CONTROLS

U.S is NOx-limited!

Jacob et al., [1993b]

U.S. GROWTH MEASURES (2008)

U.S. EMISSIONS OF OZONE PRECURSORSand trends over past 20 years

Anthropogenic VOCs

Fuel combustion• vehicles• power plants

•Fuel combustion & transport• Solvents

• Vehicles• Fires

Isoprene (biogenic VOC)

Vegetation

Flat/down

Down 30%

Down 40%

Flat

OZONE TRENDS IN U.S. http://www.epa.gov/airtrends/

National trend

Fort Collins trend

TREND IN 4th-HIGHEST 8-HOUR OZONE,2004-2006 vs 1990-1992

                                                      

                                                                                 

DEPENDENCE OF OZONE PRODUCTION ON NOx AND HYDROCARBONS

HOxfamily

OH

RO2 RO

HO2

HNO3 H2O2O3

O3

O3

PHOx

4

5

67

89

1/ 23 7

8

( ) 2 ( ) [ ]HOxPP O k NO

k4

39 2

2 [ ]( )

[ ][ ]HOxk P RH

P Ok NO M

“NOx- saturated” or“hydrocarbon-limited” regime

“NOx-limited” regime

RH

NO

O2

NO

NO2, M

NET: RH + 4O2 R’CHO + 2O3 + H2O

ALTHOUGH THE O3 PRODUCTION RATE IS ~ [NOx],THE TOTAL O3 PRODUCED IS HYDROCARBON-DEPENDENT

AND [O3] = f(ENOx) IS STRONGLY NONLINEAR

NO NO2 HNO3hv

HO2,RO2,O3 OH, O3

P(O3) L(NOx)

3 7 2 4

9 2 9 2

( ) 2 [ ][ ] 2 [ ]

( ) [ ][ ] [ ]OPE =

x

P O k HO NO k RH

L NO k NO OH k NO

Emission Deposition

Assuming NOx steady state, efficient HOx cycling, and loss of NO2 by reaction with OH:

OPE as NOx strong nonlinearity

Define ozone production efficiency (OPE) as the total number of O3 molecules produced per unit NOx emitted.

1999-2004 NOx EMISSION REDUCTIONSAND SIMULATED EFFECTS ON SURFACE OZONE

Hudman et al. [2008]50% decrease in power plant emissions20% decrease in total U.S. emissions

TRENDS IN 4th-HIGHEST 8-HOUR OZONEAT NATIONAL PARKS, 1992-2001 [EPA, 2003]

                                                               

                                                                             

OBSERVED TREND IN OZONE BACKGROUND OVER CALIFORNIA IN SPRING SUGGESTS 10-15 ppbv INCREASE

OVER PAST 20 YEARS

Trend: 0.5-0.8 ppbv yr-1Jaffe et al. [2003]

Background: concentration that would be present in absence of localanthropogenic emissions

RISING OZONE BACKGROUND IN EUROPE

3-5 km

polluted

backgroundNaja et al. [2003]

Hohenpeissenberg/Payerne

Mace Head, 1987-2004 [Simmonds et al., 2004]

Changes in anthrop. NOx emissions

HEMISPHERIC OZONE POLLUTION:IMPLICATIONS OF ENHANCED OZONE BACKGROUND

FOR MEETING AIR QUALITY STANDARDS (AQS)

0 20 40 60 80 100 120 ppbv

Europe AQS(seasonal)

U.S. AQS(8-h avg.)

U.S. AQS(1-h avg.)

Preindustrialozone

background

Present-day ozone background at

northern midlatitudes

Europe AQS (8-h avg.)

Was here until 2008!

GLOBAL OZONE BACKGROUND:METHANE AND NOx ARE THE LIMITING PRECURSORS

240

250

260

270

280

290

300

310

320

3301995 base case

50% methane

50% NOx

50% NMVOCs

50%NOx+NMVOCs

50% CO

50% all

natural

GEOS-Chem model [Fiore et al., 2002]

Anthropogenic methane enhances surface ozone by 4-6 ppbv worldwide

Sensitivity of global tropospheric ozone inventory (Tg) to 50% global reductionsin anthropogenic precursor emissions

PROJECTIONS OF GLOBAL NOx EMISSIONS

109 atoms N cm-2 s-1

AnthropogenicNOx emissions[IPCC, 2001]

2000

2020

“Optimistic” IPCC scenario: OECD, U.S. 20%, Asia 50%

EFFECT OF INCREASING SIBERIAN FOREST FIRES ON SUMMER SURFACE OZONE IN PACIFIC NORTHWEST

Mean summer 2003 enhancementof 5-9 ppbv (9-17 ppbv in events)

Jaffe et al. [2004]

Observations GEOS-Chem ozone enhancements

Siberian fires

Ozone

EFFECT OF CLIMATE CHANGE ON OZONE AIR QUALITYProbability of max 8-h O3 > 84 ppbvvs. daily max. T

Lin et al. [Atm. Env. 2001]

Correlation of high ozone with temperature is driven by(1) stagnation, (2) biogenic hydrocarbon emissions, (3) chemistry

Ozone exceedances of 90 ppbv,summer 2003

EFFECT OF CLIMATE CHANGE ON REGIONAL STAGNATION

Pollution episodes double in duration in 2050 due to decreasing frequency of cyclones ventilating the eastern U.S; expected result of greenhouse warming.

2045-2052

1995-2002

GISS GCM simulations for 2050 vs. present-day climate using pollution tracers with constant emissions

Mickley et al. [2004]

summer

weather map illustratingcyclonic ventilation of the eastern U.S.