BackgroundGround-level concentrations of ozone (O3) and fine particulate matter [≤ 2.5 μm in aerodynamic diameter (PM2.5)] have increased since preindustrial times in urban and rural regions and are associated with cardiovascular and respiratory mortality.ObjectivesWe estimated the global burden of mortality due to O3 and PM2.5 from anthropogenic emissions using global atmospheric chemical transport model simulations of preindustrial and present-day (2000) concentrations to derive exposure estimates.MethodsAttributable mortalities were estimated using health impact functions based on long-term relative risk estimates for O3 and PM2.5 from the epidemiology literature. Using simulated concentrations rather than previous methods based on measurements allows the inclusion of rural areas where measurements are often unavailable and avoids making assumptions for background air pollution.ResultsAnthropogenic O3 was associated with an estimated 0.7 ± 0.3 million respiratory mortalities (6.3 ± 3.0 million years of life lost) annually. Anthropogenic PM2.5 was associated with 3.5 ± 0.9 million cardiopulmonary and 220,000 ± 80,000 lung cancer mortalities (30 ± 7.6 million years of life lost) annually. Mortality estimates were reduced approximately 30% when we assumed low-concentration thresholds of 33.3 ppb for O3 and 5.8 μg/m3 for PM2.5. These estimates were sensitive to concentration thresholds and concentration–mortality relationships, often by > 50%.ConclusionsAnthropogenic O3 and PM2.5 contribute substantially to global premature mortality. PM2.5 mortality estimates are about 50% higher than previous measurement-based estimates based on common assumptions, mainly because of methodologic differences. Specifically, we included rural populations, suggesting higher estimates; however, the coarse resolution of the global atmospheric model may underestimate urban PM2.5 exposures.

Actions to reduce greenhouse gas (GHG) emissions often reduce co-emitted air pollutants, bringing co-benefits for air quality and human health. Past studies1–6 typically evaluated near-term and local co-benefits, neglecting the long-range transport of air pollutants7–9, long-term demographic changes, and the influence of climate change on air quality10–12. Here we simulate the co-benefits of global GHG reductions on air quality and human health using a global atmospheric model and consistent future scenarios, via two mechanisms: a) reducing co-emitted air pollutants, and b) slowing climate change and its effect on air quality. We use new relationships between chronic mortality and exposure to fine particulate matter13 and ozone14, global modeling methods15, and new future scenarios16. Relative to a reference scenario, global GHG mitigation avoids 0.5±0.2, 1.3±0.5, and 2.2±0.8 million premature deaths in 2030, 2050, and 2100. Global average marginal co-benefits of avoided mortality are $50–380 (ton CO2)−1, which exceed previous estimates, exceed marginal abatement costs in 2030 and 2050, and are within the low range of costs in 2100. East Asian co-benefits are 10–70 times the marginal cost in 2030. Air quality and health co-benefits, especially as they are mainly local and near-term, provide strong additional motivation for transitioning to a low-carbon future.

Increased concentrations of ozone and fine particulate matter (PM 2.5 ) since preindustrial times reflect increased emissions, but also contributions of past climate change. Here we use modeled concentrations from an ensemble of chemistry-climate models to estimate the global burden of anthropogenic outdoor air pollution on present-day premature human mortality, and the component of that burden attributable to past climate change. Using simulated concentrations for 2000 and 1850 and concentration-response functions (CRFs), we estimate that, at present, 470 000 (95% confidence interval, 140 000 to 900 000) premature respiratory deaths are associated globally and annually with anthropogenic ozone, and 2.1 (1.3 to 3.0) million deaths with anthropogenic PM 2.5 -related cardiopulmonary diseases (93%) and lung cancer (7%). These estimates are smaller than ones from previous studies because we use modeled 1850 air pollution rather than a counterfactual low concentration, and because of different emissions. Uncertainty in CRFs contributes more to overall uncertainty than the spread of model results. Mortality attributed to the effects of past climate change on air quality is considerably smaller than the global burden: 1500 (−20 000 to 27 000) deaths yr −1 due to ozone and 2200 (−350 000 to 140 000) due to PM 2.5 . The small multi-model means are coincidental, as there are larger ranges of results for individual models, reflected in the large uncertainties, with some models suggesting that past climate change has reduced air pollution mortality.

Background: Tropospheric ozone and black carbon (BC), a component of fine particulate matter (PM ≤ 2.5 µm in aerodynamic diameter; PM2.5), are associated with premature mortality and they disrupt global and regional climate.Objectives: We examined the air quality and health benefits of 14 specific emission control measures targeting BC and methane, an ozone precursor, that were selected because of their potential to reduce the rate of climate change over the next 20–40 years.Methods: We simulated the impacts of mitigation measures on outdoor concentrations of PM2.5 and ozone using two composition-climate models, and calculated associated changes in premature PM2.5- and ozone-related deaths using epidemiologically derived concentration–response functions.Results: We estimated that, for PM2.5 and ozone, respectively, fully implementing these measures could reduce global population-weighted average surface concentrations by 23–34% and 7–17% and avoid 0.6–4.4 and 0.04–0.52 million annual premature deaths globally in 2030. More than 80% of the health benefits are estimated to occur in Asia. We estimated that BC mitigation measures would achieve approximately 98% of the deaths that would be avoided if all BC and methane mitigation measures were implemented, due to reduced BC and associated reductions of nonmethane ozone precursor and organic carbon emissions as well as stronger mortality relationships for PM2.5 relative to ozone. Although subject to large uncertainty, these estimates and conclusions are not strongly dependent on assumptions for the concentration–response function.Conclusions: In addition to climate benefits, our findings indicate that the methane and BC emission control measures would have substantial co-benefits for air quality and public health worldwide, potentially reversing trends of increasing air pollution concentrations and mortality in Africa and South, West, and Central Asia. These projected benefits are independent of carbon dioxide mitigation measures. Benefits of BC measures are underestimated because we did not account for benefits from reduced indoor exposures and because outdoor exposure estimates were limited by model spatial resolution.

[1] Ozone (O 3 ) precursor emissions influence regional and global climate and air quality through changes in tropospheric O 3 and oxidants, which also influence methane (CH 4 ) and sulfate aerosols (SO 4 2À With a radiative transfer model that includes greenhouse gases and the aerosol direct effect, we find that regional NO x reductions produce global, annually averaged positive net RFs (0.2 AE 0.6 to 1.7 AE 2 mWm À2 /Tg N yr À1 ), with some variation among models. Negative net RFs result from reductions in global CH 4 (À162.6 AE 2 mWm À2 for a change from 1760 to 1408 ppbv CH 4 ) and regional NMVOC (À0.4 AE 0.2 to À0.7 AE 0.2 mWm À2 /Tg C yr À1 ) and CO emissions (À0.13 AE 0.02 to À0.15 AE 0.02 mWm À2 /Tg CO yr À1 ). Including the effect of O 3 on CO 2 uptake by vegetation likely makes these net RFs more negative by À1.9 to À5.2 mWm À2 /Tg N yr À1 , À0.2 to À0.7 mWm À2 /Tg C yr À1 , and À0.02 to À0.05 mWm À2 / Tg CO yr À1 . Net RF impacts reflect the distribution of concentration changes, where RF is affected locally by changes in SO 4 2À , regionally to hemispherically by O 3 , and globally by CH 4 . Global annual average SO 4 2À responses to oxidant changes range from 0.4 AE 2.6 to À1.9 AE 1.3 Gg for NO x reductions, 0.1 AE 1.2 to À0.9 AE 0.8 Gg for NMVOC reductions, and À0.09 AE 0.5 to À0.9 AE 0.8 Gg for CO reductions, suggesting additional research is needed. The 100-year global warming potentials (GWP 100 ) are calculated for the global CH 4 reduction (20.9 AE 3.7 without stratospheric O 3 or water vapor, 24.2 AE 4.2 including those components), and for the regional NO x , NMVOC, and CO reductions (À18.7 AE 25.9 to À1.9 AE 8.7 for NO x , 4.8 AE 1.7 to 8.3 AE 1.9 for NMVOC, and 1.5 AE 0.4 to 1.7 AE 0.5 for CO). Variation in GWP 100 for NO x , NMVOC, and CO suggests that regionally specific GWPs may be necessary and could support the inclusion of O 3 precursors in future policies that address air quality and climate change simultaneously. Both global net RF and GWP 100 are more sensitive to NO x and NMVOC reductions from South Asia than the other three regions.Citation: Fry, M. M., et al. (2012), The influence of ozone precursor emissions from four world regions on tropospheric composition and radiative climate forcing,