Effect of NO x emission controls on the long-range transport of ozone air pollution and human mortality J. Jason West, Vaishali Naik, Larry W. Horowitz, Arlene M. Fiore

What is the effect of NO x reductions in one region, on ozone in all other world regions? Reduce anthropogenic NO x emissions by 10% in each of 9 world regions, in the MOZART-2 global CTM (MACCM3 meteorology, EDGAR emissions for 1990s). Naik et al. (JGR, 2005) used these simulations to show that NO x reductions in each region increase net RF.

Change in surface O 3 (ppb), averaged over the 3-month period with highest population-weighted O 3 in source region. Surface O 3 Change from 10% regional NO x reductions

Effect of 10% regional NO x reductions NAEUFSUAFINEASASEAU NA EU FSU AF IN EA SA SE AU Receptor Region Source Region Change in population-weighted O 3 (ppt), averaged over the 3-month period with highest O 3 in the receptor region.

Normalized source-receptor matrix NAEUFSUAFINEASASEAU NA EU FSU AF IN EA SA SE AU Receptor Region Source Region Change in 3-month population-weighted average O 3 per unit change in NO x emissions (ppb (Tg N yr -1 ) -1 ).

Example: Europe EU as source EU as receptor per Tg N Change in population-weighted O 3, averaged over the 3-month period with highest O 3 in the receptor region.

Example: North America NA as source NA as receptor per Tg N Change in population-weighted O 3, averaged over the 3-month period with highest O 3 in the receptor region.

Monthly O 3 changes in each receptor region Panels for receptor regions, showing effects of 10% NO x reductions in each source region, for population-weighted monthly average O 3.

Why greater sensitivity to changes in emissions in tropics and SH? dO 3 Burden dO 3 Burden / dEmis dO 3 Production / dEmis Fraction of dO 3 Production above 500 mb dO 3 Export from source region dO 3 Production outside of source region NA EU FSU AF IN EA SA SE AU Source Region ** Mainly due to decreased O 3 production below 500 mb. Units are: Tg O 3, Tg O 3 (TgN yr -1 ) -1, Tg O 3 yr -1 (TgN yr -1 ) -1

Is ozone exported or NO y ? Export greater

Effects on Metropolitan Regions Los Angeles Toronto London Athens Moscow Tehran Delhi HongKong Bangkok NA EU FSU AF IN EA SA SE AU Receptor Source Region Change in 3-month population-weighted average O 3 (ppt).

Avoided Mortalities (annual) Receptor Region Source Region Mortality based on Bell et al. (2004) Intra-regional avoided mortalities: 5744; Inter-regional: 2600 NAEUFSUAFINEASASEAUTOT NA EU FSU AF IN EA SA SE AU TOT8344

Avoided Mortalities (annual) per Tg N yr -1 Receptor Region Source Region NAEUFSUAFINEASASEAUTOT NA EU FSU AF IN EA SA SE AU TOT345

Long-term changes in O 3 via CH 4 NO X O3O3 OH CH 4 O3O3 rapid local decadal global EU as source EU as receptor per Tg N

Long-term changes in O 3 via CH 4 CH 4 and long-term O 3 increase per unit NO x decrease (global annual average surface O 3 change) Tropical and SH regions have much greater effect on CH 4 and long-term O 3 per ton NO x reduced

Conclusions Based on 10% regional anthropogenic NO x emission reductions: Inter-continental effects are ~10x smaller than effects within a region. –Largest impact is Europe on the Former Soviet Union. –Control costs would need to be ~10% of within-region cost for overseas reductions to be cost-effective. Tropical regions cause a greater ∆O 3 per ton NO x reduced, than temperate regions. Avoided mortalities are greater outside of NA, EU, and FSU than within. Long-term changes in O 3 (via CH 4 ) roughly cancel the short-term O 3 reduction for some region pairs.

CONTINENT 2 OCEAN Boundary layer (0-3 km) Free Troposphere CONTINENT 1 Ozone Precursors Affect Both Ozone Air Quality and Climate Forcing OH HO 2 NMVOC, CO, CH 4 NO NO 2 h O3O3 Direct Intercontinental Transport Global Background O 3 NO x NMVOCs O3O3 NO x NMVOCs O3O3

Ozone Precursors Affect Both Ozone Air Quality and Climate Forcing NO X O3O3 OH CH 4 O3O3 VOCs, CO O3O3 OH CH 4 O3O3 OHHO 2 NONO 2 h O3O3 NMVOCs, CO, CH 4 rapid local decadal global CH 4 O3O3 OH CH 4 O3O3 decadal global

Surface ozone changes due to 20% anthropogenic reductions Effect of global 20% anthropogenic emission reductions on 8-hr daily maximum surface O 3, averaged over 3 month period with highest O 3, at steady state (MOZART-2).

Ozone changes Effects of 20% reductions in anthropogenic emissions Tropospheric O 3 burden ∆O 3 srf global population-weighted 8hr. 3-month ∆O 3 srf annual average Short term Steady state NO X O3O3 OH CH 4 O3O3 Short term Long term Steady state = Short term + Long term

Radiative forcing Effects of 20% reductions in anthropogenic emissions METHANE OZONE NO X O3O3 OH CH 4 O3O3 CH 4 forcing estimated using Ramaswamy et al. (2001), O 3 forcing using GFDL AM2 radiative transfer model.

Radiative Forcing and Ozone Air Quality Effects of 20% reductions in anthropogenic emissions METHANE OZONE Radiative Forcing ∆ RF net / ∆ O 3 srf Reducing methane emissions causes the greatest reduction in RF per unit improvement in O 3 air quality. Ozone air quality ∆O 3 srf global population- weighted 8hr. 3-month West et al. (2007) GRL

Human Health Effects of Ozone and PM Time-series studies: relate short-term (day-to-day) changes in concentration to daily mortality rates Cohort studies: relate community-level exposures over multiple years to annual mortality Relative Risk (RR) = the ratio of the probability of health outcome in exposed group vs. unexposed group Bell et al., 2004 Mortality effects of ozone in short-term time-series studies: Mortality effects of PM in long-term cohort studies: Pope et al., 2002

Mitigating Global Ozone Pollution by Reducing Methane Emissions: Global Health Benefits Motivation Methane, the most abundant VOC, contributes to the growing global background of tropospheric ozone. Methane mitigation has been considered for climate, but not for air quality. GOAL: Consider the viability of methane control for managing tropospheric ozone, by considering the costs of control and benefits for avoided human mortality. Change in surface ozone from a 20% reduction in global anthropogenic methane emissions. Methane mitigation decreases O 3 everywhere (using MOZART-2, steady-state relative to 2030 A2). ∆O 3 = ppbv (glob. Ann. Avg. 8- hr. O 3, population-weighted).

Mitigating Global Ozone Pollution by Reducing Methane Emissions: Global Health Benefits Global avoided premature mortalities from a 20% reduction in global anthropogenic methane emissions. Prevents ~30,000 premature mortalities in 2030 (~0.04% of total deaths), and ~370,000 from Conclusions Methane emission reductions decrease ozone everywhere, while also reducing greenhouse warming. Monetized health benefits are ~$240 per ton CH 4 ($12 per ton CO 2 eq.) - which can justify the 20% methane reduction. Methane abatement can be a cost-effective component of international long-term ozone management. Ozone concentration Historical Background Regional Local Standard Future Continued domestic emission controls Opportunity for global methane controls West et al. (2006) PNAS

OHHO 2 NONO 2 h O3O3 NMVOCs, CO Ozone Precursors Affect Both Ozone Air Quality and Climate Forcing Urban Global OHHO 2 NONO 2 h O3O3 NMVOCs, CO, CH 4

Is ozone exported or NO x ? dO 3 Burden dO 3 Burden / dEmis dO 3 Production / dEmis Fraction of dO 3 Production above 500 mb dO 3 Export from source region dO 3 Production outside of source region NA EU FSU AF IN EA SA SE AU Source Region

Ozone changes Effects of 20% reductions in anthropogenic emissions Tropospheric O 3 burden ∆O 3 srf global population-weighted 8hr. 3-month ∆O 3 srf annual average Short term Steady state NO X O3O3 OH CH 4 O3O3

Effect of 10% regional NO x reductions at steady state NAEUFSUAFINEASASEAU NA EU FSU AF IN EA SA SE AU Receptor Region Source Region Change in 3-month population-weighted average O 3 (ppt)