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Surface-level ozone (O3) is a secondary air pollutant that has adverse effects on human health. In the troposphere, O3 is produced in complex cycles of photochemical reactions involving nitrogen oxides (NOx) and volatile organic compounds (VOCs). Determining if O3 levels will be decreased by lowering NOx emissions (“NOx-sensitive”), VOC emissions (“VOC-sensitive”), or both (“the transition zone”) can be done by using the formaldehyde (HCHO; a VOC species) to nitrogen dioxide (NO2; a component of NOx) concentration ratio (HCHO/NO2; “FNR”). Generally, lower FNR values indicate VOC sensitivity, while higher values indicate NOx sensitivity. Despite being a highly populated region with coastal O3 air quality issues, the Lake Michigan region in the United States, including the Chicago, Illinois, metropolitan area (CMA), remains relatively understudied, especially from the satellite perspective. In this work, we present the first study that utilizes TROPOspheric Monitoring Instrument (TROPOMI) satellite data over the Lake Michigan region from 2019–2021 to assess changes in O3 precursor levels and the inferred O3 chemistry sensitivity between (1) O3 season days and CMA O3 exceedance days and (2) weekdays and weekends. Higher NO2 vertical column densities (VCDs), HCHO VCDs, and FNR values are seen throughout the study domain on exceedance days, indicating generally more NOx-sensitive O3 chemistry. The largest change occurs in the areal extent of the transition zone, which decreases by 40 % during exceedance days. Major urban cores in the domain (e.g., Chicago, Illinois; Gary, Indiana; and Milwaukee, Wisconsin) remain VOC-sensitive on exceedance days as the higher NO2 VCDs in these areas counterbalance the regionally higher HCHO VCDs. Utilizing 10 m wind analysis data, we show that the lake breeze circulation is stronger on exceedance days. The strengthening of the lake breeze causes stronger convergence of the wind field along the southwestern Lake Michigan coastline, which can concentrate NO2 emissions originating in this area. This finding provides a possible explanation for the higher TROPOMI NO2 VCDs over the urban core of Chicago on exceedance days. Investigation of 2 m air temperature analysis data reveals that temperatures are higher on exceedance days, which explains the stronger lake breeze circulation and provides a possible cause for the higher TROPOMI HCHO VCDs over the entire region (due to increased temperature-dependent biogenic VOC emissions). Comparing weekdays and weekends, higher FNR values throughout much of the region indicate increasingly NOx-sensitive O3 chemistry on weekends. These changes are driven by lower NO2 VCDs in urban areas, particularly in Chicago, and higher HCHO VCDs in the southern part of the domain on weekends. Overall, our analyses suggest that VOC emissions controls in major urban areas and NOx emissions controls throughout the entire domain are necessary to decrease O3 levels in the Lake Michigan region.

Background: Exposure to ozone and fine particulate matter (PM2.5) can cause adverse health effects, including premature mortality due to cardiopulmonary diseases and lung cancer. Recent studies quantify global air pollution mortality but not the contribution of different emissions sectors, or they focus on a specific sector. Objectives: We estimated the global mortality burden of anthropogenic ozone and PM2.5, and the impact of five emissions sectors, using a global chemical transport model at a finer horizontal resolution (0.67° × 0.5°) than previous studies. Methods: We performed simulations for 2005 using the Model for Ozone and Related Chemical Tracers, version 4 (MOZART-4), zeroing out all anthropogenic emissions and emissions from specific sectors (All Transportation, Land Transportation, Energy, Industry, and Residential and Commercial). We estimated premature mortality using a log-linear concentration–response function for ozone and an integrated exposure–response model for PM2.5. Results: We estimated 2.23 (95% CI: 1.04, 3.33) million deaths/year related to anthropogenic PM2.5, with the highest mortality in East Asia (48%). The Residential and Commercial sector had the greatest impact globally—675 (95% CI: 428, 899) thousand deaths/year—and in most regions. Land Transportation dominated in North America (32% of total anthropogenic PM2.5 mortality), and it had nearly the same impact (24%) as Residential and Commercial (27%) in Europe. Anthropogenic ozone was associated with 493 (95% CI: 122, 989) thousand deaths/year, with the Land Transportation sector having the greatest impact globally (16%). Conclusions: The contributions of emissions sectors to ambient air pollution–related mortality differ among regions, suggesting region-specific air pollution control strategies. Global sector-specific actions targeting Land Transportation (ozone) and Residential and Commercial (PM2.5) sectors would particularly benefit human health. Citation: Silva RA, Adelman Z, Fry MM, West JJ. 2016. The impact of individual anthropogenic emissions sectors on the global burden of human mortality due to ambient air pollution. Environ Health Perspect 124:1776–1784; http://dx.doi.org/10.1289/EHP177

Atmospheric models are essential tools to study the behavior of air pollutants. To interpret the complicated atmospheric model simulations, a new-generation Model Visualization and Analysis Tool (Model-VAT) has been developed for scientists to analyze the model data and visualize the simulation results. The Model-VAT incorporates analytic functions of conventional tools and enhanced capabilities in flexibly accessing, analyzing, and comparing simulated results from multi-scale models with different map projections and grid resolutions. The performance of the Model-VAT is demonstrated by a case study of investigating the influence of boundary conditions (BCs) on the ambient Hg formation and transport simulated by the CMAQ model over the Pearl River Delta (PRD) region. The alternative BC options are taken from (1) default time-independent profiles, (2) outputs from a CMAQ simulation of a larger nesting domain, and (3) concentration files from GEOS-Chem (re-gridded and re-projected using the Model-VAT). The three BC inputs and simulated ambient concentrations and deposition were compared using the Model-VAT. The results show that the model simulations based on the static BCs (default profile) underestimates the Hg concentrations by ~6.5%, dry depositions by ~9.4%, and wet depositions by ~43.2% compared to those of the model-derived (e. g. GEOS-Chem or nesting CMAQ) BCs. This study highlights the importance of model nesting approach and demonstrates that the innovative functions of Model-VAT enhances the efficiency of analyzing and comparing the model results from various atmospheric model simulations.

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.

The impacts of aviation emissions on current and future year fine particulate matter (PM2.5) were investigated using the Community Multiscale Air Quality model, accounting for aviation emissions from 99 airports and below 3 km during landing and takeoff (LTO) cycles. Results indicated that current year aviation emissions increased annual average PM2.5 concentrations by 3.2 ng m−3 (0.05%) in the continental U.S. while projected 2025 aviation emissions increased annual average PM2.5 by 11.2 ng m−3 (0.20%). Ammonium nitrate aerosol was the largest contributor to the increase in PM2.5 concentrations, particularly in the future year. Using an indicator of inorganic PM2.5 change, we attributed ammonium nitrate aerosol contributions in both years to excess free ammonia (8% higher NH3 and 35% lower NOx emissions from non-aviation sources in 2025 than 2005), and higher aircraft emissions of NOx (which when converted to HNO3 forms ammonium nitrate aerosol) than SO2 (a precursor of ammonium sulfate aerosol). Our findings highlight the critical role that non-aviation emissions play in assessing the air quality impacts of aviation emissions in a future year scenario.

Excess wet and dry deposition of nitrogen-containing compounds is a concern at a number of national parks. The Rocky Mountain Atmospheric Nitrogen and Sulfur Study (RoMANS) was conducted during the spring and summer of 2006 to identify the overall mix of ambient and deposited sulfur and nitrogen at Rocky Mountain National Park (RMNP), in north-central Colorado. The Comprehensive Air Quality Model with extensions (CAMx) was used to simulate the fate of gaseous and particulate species subjected to multiple chemical and physical processes during RoMANS. This study presents an operational evaluation with a special emphasis on the model performance of reduced nitrogen species. The evaluation showed large negative biases and errors at RMNP and the entire domain for ammonia; therefore the model was considered inadequate for future source apportionment applications. The CAMx Integrated Processes Rate (IPR) analysis tool was used to elucidate the potential causes behind the poor model performance. IPR served as a tool to diagnose the relative contributions of individual physical and chemical processes to the final concentrations of reduced nitrogen species. The IPR analysis revealed that dry deposition is the largest sink of ammonia in the model, with some cells losing almost 100% of the available mass. Closer examination of the ammonia dry deposition velocities in CAMx found that they were up to a factor of 10 larger than those reported in the literature. A series of sensitivity simulations were then performed by changing the original deposition velocities with a simple multiplicative scaling factor. These simulations showed that even when the dry deposition values were altered to reduce their influence, the model was still unable to replicate the observed time series; i.e., it fixed the average bias, but it did not improve the precision.

A prototype online photolysis module has been developed for the Community Multiscale Air Quality (CMAQ) modeling system. The module calculates actinic fluxes and photolysis rates (j values) at every vertical level in each of seven wavelength intervals from 291 to 850 nm, as well as the total surface irradiance and aerosol optical depth within each interval. The module incorporates updated opacity at each time step, based on changes in local ozone, nitrogen dioxide, and particle concentrations. The module is computationally efficient and requires less than 5% more central processing unit time than using the existing CMAQ “lookup” table method for calculating j values. The main focus of the work presented here is to describe the new online module as well as to highlight the differences between the effective cross sections from the lookup-table method currently being used and the updated effective cross sections from the new online approach. Comparisons of the vertical profiles for the photolysis rates for nitrogen dioxide (NO2) and ozone (O3) from the new online module with those using the effective cross sections from a standard CMAQ simulation show increases in the rates of both NO2 and O3 photolysis.

The Emission Scenario Projection (ESP) method produces future-year air pollutant emissions for mesoscale air quality modeling applications. We present ESP v2.0, which expands upon ESP v1.0 by spatially allocating future-year non-power sector emissions to account for projected population and land use changes. In ESP v2.0, US Census division-level emission growth factors are developed using an energy system model. Regional factors for population-related emissions are spatially disaggregated to the county level using population growth and migration projections. The county-level growth factors are then applied to grow a base-year emission inventory to the future. Spatial surrogates are updated to account for future population and land use changes, and these surrogates are used to map projected county-level emissions to a modeling grid for use within an air quality model. We evaluate ESP v2.0 by comparing US 12 km emissions for 2005 with projections for 2050. We also evaluate the individual and combined effects of county-level disaggregation and of updating spatial surrogates. Results suggest that the common practice of modeling future emissions without considering spatial redistribution over-predicts emissions in the urban core and under-predicts emissions in suburban and exurban areas. In addition to improving multi-decadal emission projections, a strength of ESP v2.0 is that it can be applied to assess the emissions and air quality implications of alternative energy, population and land use scenarios.

Background Reductions in greenhouse gas emissions often reduce emissions of coemitted air pollutants, yielding cobenefits for air quality and human health. Here, we report results of a global cobenefits study—the first to use a global atmospheric model and consistent future scenarios—and results from follow-on studies that downscale those global results to focus on the continental US. Methods We use the RCP4.5 scenario as an aggressive global greenhouse gas mitigation scenario, and compare it with its associated reference case, the difference between these scenarios is uniquely attributable to the global carbon policy. Findings In the global study, we find that global greenhouse gas mitigation avoids roughly 0·5 million air pollution-related deaths per year in 2030, 1·3 million air pollution-related deaths per year in 2050, and 2·2 million air pollution-related deaths per year in 2100. Global average cobenefits are US$50–380 per ton of CO2 reduced, which exceeds previous estimates. These cobenefits also exceed the marginal abatement costs in 2030 and 2050. Cobenefits here are higher than in previous studies because we account for global air pollution transport, and because of projected population, and baseline mortality growth. We then downscale these results in 2050 to the continental USA to project these cobenefits at fine resolution, using the WRF, SMOKE and CMAQ models, and we separate the contributions of domestic and foreign reductions to US cobenefits. We find that for PM2.5, most of the air quality and health cobenefits are from domestic emissions. By contrast, for ozone, most of the cobenefits results from foreign emissions, including global methane reductions. Interpretation These results suggest that the air quality and health cobenefits realised by one country will be much greater if foreign countries also reduce greenhouse gas emissions in a coordinated effort. We also conclude that previous studies that focus on domestic or local cobenefits might significantly underestimate the total cobenefits of global greenhouse gas reductions. Funding US Environmental Protection Agency, the Integrated Assessment Research Program in the US Department of Energy, Office of Science, the National Institute of Environmental Health Sciences, the Portuguese Foundation for Science and Technology, and an EPA STAR Graduate Fellowship.

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.

Non-methane volatile organic compounds (NMVOCs) influence air quality and global climate change through their effects on secondary air pollutants and climate forcers. Here we simulate the air quality and radiative forcing (RF) impacts of changes in ozone, methane, and sulfate from halving anthropogenic NMVOC emissions globally and from 10 regions individually, using a global chemical transport model and a standalone radiative transfer model. Halving global NMVOC emissions decreases global annual average tropospheric methane and ozone by 36.6 ppbv and 3.3 Tg, respectively, and surface ozone by 0.67 ppbv. All regional reductions slow the production of peroxyacetyl nitrate (PAN), resulting in regional to intercontinental PAN decreases and regional NOx increases. These NOx increases drive tropospheric ozone increases nearby or downwind of source regions in the Southern Hemisphere (South America, Southeast Asia, Africa, and Australia). Some regions' NMVOC emissions contribute importantly to air pollution in other regions, such as East Asia, the Middle East, and Europe, whose impact on US surface ozone is 43%, 34%, and 34% of North America's impact. Global and regional NMVOC reductions produce widespread negative net RFs (cooling) across both hemispheres from tropospheric ozone and methane decreases, and regional warming and cooling from changes in tropospheric ozone and sulfate (via several oxidation pathways). The 100 yr and 20 yr global warming potentials (GWP100, GWP20) are 2.36 and 5.83 for the global reduction, and 0.079 to 6.05 and −1.13 to 18.9 among the 10 regions. The NMVOC RF and GWP estimates are generally lower than previously modeled estimates, due to the greater NMVOC/NOx emissions ratios simulated, which result in less sensitivity to NMVOC emissions changes and smaller global O3 burden responses, in addition to differences in the representation of NMVOCs and oxidation chemistry among models. Accounting for a fuller set of RF contributions may change the relative magnitude of each region's impacts. The large variability in the RF and GWP of NMVOCs among regions suggest that regionally specific metrics may be necessary to include NMVOCs in multi-gas climate trading schemes.

Carbon monoxide (CO) emissions influence global and regional air quality and global climate change by affecting atmospheric oxidants and secondary species. We simulate the influence of halving anthropogenic CO emissions globally and individually from 10 regions on surface and tropospheric ozone, methane, and aerosol concentrations using a global chemical transport model (MOZART-4 for the year 2005). Net radiative forcing (RF) is then estimated using the GFDL (Geophysical Fluid Dynamics Laboratory) standalone radiative transfer model. We estimate that halving global CO emissions decreases global annual average concentrations of surface ozone by 0.45 ppbv, tropospheric methane by 73 ppbv, and global annual net RF by 36.1 mW m−2, nearly equal to the sum of changes from the 10 regional reductions. Global annual net RF per unit change in emissions and the 100 yr global warming potential (GWP100) are estimated as −0.124 mW m−2 (Tg CO)−1 and 1.34, respectively, for the global CO reduction, and ranging from −0.115 to −0.131 mW m−2 (Tg CO)−1 and 1.26 to 1.44 across 10 regions, with the greatest sensitivities for regions in the tropics. The net RF distributions show widespread cooling corresponding to the O3 and CH4 decreases, and localized positive and negative net RFs due to changes in aerosols. The strongest annual net RF impacts occur within the tropics (28° S–28° N) followed by the northern midlatitudes (28° N–60° N), independent of reduction region, while the greatest changes in surface CO and ozone concentrations occur within the reduction region. Some regional reductions strongly influence the air quality in other regions, such as East Asia, which has an impact on US surface ozone that is 93% of that from North America. Changes in the transport of CO and downwind ozone production clearly exceed the direct export of ozone from each reduction region. The small variation in CO GWPs among world regions suggests that future international climate agreements could adopt a globally uniform metric for CO with little error, or could use different GWPs for each continent. Doing so may increase the incentive to reduce CO through coordinated policies addressing climate and air quality.