.

s

Yuqiang Zhang1, J. Jason West1, Meridith M. Fry1, Raquel A. Silva1, Steven J. Smith2, Vaishali Naik4, Zachariah Adelman1, Susan C. Anenberg3, Larry W. Horowitz4, Jean-Francois Lamarque5, Louisa Emmons5

1 Environmental Sciences and Engineering, Univ. of North Carolina, Chapel Hill. 2 Joint Global Change Research Institute. 3 US Environmental Protection Agency. 4 NOAA Geophysical Fluid Dynamics Laboratory. 5 National Center for Atmospheric Research.

Acknowledgements: This work was funded by an EPA STAR grant #834285, an EPA STAR Graduate Fellowship (MMF),

the EPA Office of Air Quality Planning and Standards, and the Department of Energy Office of Science.Contact: jasonwest@unc.edu, www.unc.edu/~jjwest

Effect of changes in emissions and climate change on global air quality:A study of the air quality co-benefits of GHGs mitigation

834285

1. Introduction

Sources & Policies

Air pollutants

GHGs

Emissions Problems

Air pollution

ClimateChange2

1

Connections between air quality and climate change, showing two mechanisms of co-benefits of GHG mitigation

on air quality: #1 is immediate and local, #2 is long-term and global.

Years Emissions Meteorology Name

2000 Historical Historical 2000

2030,

2050,

2100

GCAM Reference

RCP8.5 erefm85

RCP4.5 RCP4.5 rcp45

GCAM Reference

RCP4.5 erefm45

Simulations Modeled in the study

3. Preliminary Results

• The air quality co-benefits of global GHG mitigation are substantial.

• The direct co-benefits via changes in co-emitted air pollutants (mechanism #1) appear much more important than the long-term influence via climate change (#2), even in 2100.

• Co-benefits would likely be larger if the Reference Case scenario had not assumed decreased air pollution in the future.

• Methane changes in these emissions scenarios are likely important in contributing to the tropospheric O3 burden change.

• Future work will include assessing the global health impacts of these air quality changes, and meteorological and chemical downscaling of these results to the US using the WRF and CMAQ models.

PM2.5 and O3 concentration changes in 2100Total Co-benefit #2 Meteorology Co-benefit #1 Emissions Co-benefit

5. Conclusions

Actions to reduce emissions of greenhouse gases (GHGs) will benefit global and regional air quality through two mechanisms in the future: 1) directly through reductions in emissions of co-emitted air pollutants (short-term and local), and 2) indirectly by slowing the influence of climate change on air pollution (long-term and global). While a large literature discusses the impacts of climate change on air quality, through meteorological changes, biogenic emissions, and other factors, we focus on the co-benefits of GHG mitigation on air quality.

Here we aim to quantify the global air quality benefits of GHG mitigation through these two mechanisms, in realistic future scenarios to 2100. We use the global chemical transport model MOZART-4 to simulate changes in ozone and fine particular matter (PM2.5) due to changes in co-emitted air pollutants and climate due to the GHG mitigation. We present results for the changes in global air quality due to GHG mitigation in 2030, 2050, and 2100.

• We use scenarios from the GCAM global energy economics model, developed as Representative Concentration Pathway Scenarios (RCPs) for the IPCC 5th Assessment report– a Reference Case and RCP4.5.

• In GCAM, RCP4.5 differs from the Reference Case only in the application of a climate policy. Therefore, we simulate directly the effects of global GHG mitigation on co-emitted air pollutants.

• Global meteorology for these future scenarios is from the GFDL general circulation model (AM3) simulations of RCP8.5 (with similar forcing as the Reference Case) and RCP4.5.

2. Methodology

Global and regional Air Quality Global and regional anthropogenic emissionsOC (Tg C/yr)

SO2 (Tg SO2/yr)

The emission reductions due to the GHG mitigation have a large positive effect on both PM2.5 and O3, while the changing meteorology has less influence. Slowing future climate change increases O3 in remote areas, as increasing water vapor decreases the ozone lifetime. In polluted regions, slowing climate change causes O3 to decrease due to decreasing temperature and biogenic emissions, and other meteorological factors.

PM2.5 concentration (population-weighted annual average)

O3 concentration (population-weighted 6-month of average of 1-hr daily maximum)

PM2.5

O3

4. Analysis

a

b

c

a: Total co-benefit; b: Emission co-benefit; c: Meteorology co-benefit

Methane and isoprene emission change on Tropospheric O3 burden

Over the long term, the global PM2.5 and O3 both decrease for all scenarios, reflecting the assumptions in the RCPs of a cleaner world as economic well-being increases. The air quality co-benefits of GHG mitigation are large—2.37 ug/m3 for PM2.5 and 8.11 ppb for O3, for the global population-weighted concentrations in 2100.

Anthropogenic changes of organic carbon and sulfur dioxide, due to GHGs mitigation, among different scenarios contribute

to the global and regional PM2.5 benefit. Organic carbon and sulfur dioxide play different roles in different regions.

Global North America India East Asia

NO (Tg NO/yr)

Methane concentration (ppb) ISOP emission (Tg C/a-1) ∆O3 burden (Tg /a-1)

Methane emissions changes likely contribute substantially effect the tropospheric ozone burden Changes in isoprene emissions, due to meteorological changes, have a smaller influence on tropospheric ozone burden

• We will present the total co-benefits and those resulting from the two mechanisms as:

Total co-benefit: rcp45−erefm85

Emission co-benefit: rcp45−erefm45

Meteorology co-benefit: erefm45−erefm85

Global North America East AsiaIndia

Global North America East AsiaIndia

Global North America India East Asia

Global North America India East Asia