Air Quality and Climate Connections

Abstract

Multiple linkages connect air quality and climate change. Many air pollutant sources also emit carbon dioxide (CO 2 ), the dominant anthropogenic greenhouse gas (GHG). The two main contributors to non-attainment of U.S. ambient air quality standards, ozone (O 3 ) and particulate matter (PM), interact with radiation, forcing climate change. PM warms by absorbing sunlight (e.g., black carbon) or cools by scattering sunlight (e.g., sulfates) and interacts with clouds; these radiative and microphysical interactions can induce changes in precipitation and regional circulation patterns. Climate change is expected to degrade air quality in many polluted regions by changing air pollution meteorology (ventilation and dilution), precipitation and other removal processes, and by triggering some amplifying responses in atmospheric chemistry and in anthropogenic and natural sources. Together, these processes shape distributions and extreme episodes of O 3 and PM. Global modeling indicates that as air pollution programs reduce SO 2 to meet health and other air quality goals, near-term warming accelerates due to "unmasking" of warming induced by rising CO 2 . Air pollutant controls on CH 4 , a potent GHG and precursor to global O 3 levels, and on sources with high black carbon (BC) to organic carbon (OC) ratios could offset near-term warming induced by SO 2 emission reductions, while reducing global background O 3 and regionally high levels of PM. Lowering peak warming requires decreasing atmospheric CO 2 , which for some source categories would also reduce co-emitted air pollutants or their precursors. Model projections for alternative climate and air quality scenarios indicate a wide range for U.S. surface O 3 and fine PM, although regional projections may be confounded by interannual to decadal natural climate variability. Continued implementation of U.S. NO x emission controls guards against rising pollution levels triggered either by climate change or by global emission growth. Improved accuracy and trends in emission inventories are critical for accountability analyses of historical and projected air pollution and climate mitigation policies.Implications: The expansion of U.S. air pollution policy to protect climate provides an opportunity for joint mitigation, with CH 4 a prime target. BC reductions in developing nations would lower the global health burden, and for BC-rich sources (e.g., diesel) may lessen warming. Controls on these emissions could offset near-term warming induced by health-motivated reductions of sulfate (cooling). Wildfires, dust, and other natural PM and O 3 sources may increase with climate warming, posing challenges to implementing and attaining air quality standards. Accountability analyses for recent and projected air pollution and climate control strategies should underpin estimated benefits and trade-offs of future policies.

AerChemMIP: quantifying the effects of chemistry and aerosols in CMIP6

“…AerChemMIP aims to identify the patterns of chemical change at the global and regional levels, as well as the ERF associated with NTCF mitigation efforts (focusing on policy choices in areas 1 and 2 above) and their impact on climate (surface temperature and precipitation) and other environmental change (health, ecosystem, visibility, etc. ) between 2015 and 2055 (as the time frame over which aerosol and precursor emissions are expected to be significant; Shindell et al, 2012a;Fiore et al, 2015). Such impact analysis can be performed by contrasting two simulations: (a) a reference with weak air quality policies and relatively high aerosol and ozone precursor emissions; and (b) a perturbation experiment where strong air quality policies are applied, leading to much reduced NTCF emissions.…”

Synoptic meteorological modes of variability for fine particulate matter (PM<sub>2.5</sub>) air quality in major metropolitan regions of China

“…Future climate change can significantly affect synoptic-scale circulation patterns and local meteorology, modifying the transport and deposition of PM 2.5 (Fiore et al, 2015;Jiang et al, 2013;Mickley et al, 2004). Based on the demonstrated strong relationships of synoptic circulation and local meteorology on daily PM 2.5 , we build a regression model to infer how interannual variations of local and synoptic meteorology affect interannual PM 2.5 variability, which we then apply to future climate 15…”

Exploring the relationship between surface PM<sub>2.5</sub> and meteorology in Northern India

“…We additionally derive metrics from the reanalysis data that relate to air stagnation, as stagnation describes the basic meteorological conditions that are thought to exacerbate the worst pollution levels (e.g., Jacob and Winner, 2009;Fiore et al, 2012Fiore et al, , 2015and references therein). Stagnation has also been used as a proxy for air quality under future climate change (e.g., Horton et al, 2014).…”