Fine particulate matter and ozone pollution in China: recent trends, future controls, and impact of climate change Daniel J. Jacob A typical day in Beijing (2030) Viral Shah Lu Shen Shixian Zhai Ke Li Junfeng Wang Drew Pendergrass

The industrial revolution and air pollution Pittsburgh in the 1940s

London fog: first evidence of air pollution deaths Fine particulate matter (PM2.5) from domestic+industrial coal combustion “Killer fog” of December 1952 caused 10,000 deaths in 4 days Altitude inversion < 1km Sulfur dioxide (SO2) particles (PM2.5) sulfate soot Temperature Coal combustion

Los Angeles smog: first evidence of ozone air pollution Respiratory problems, vegetation damage due to high surface ozone altitude produced by photolysis of oxygen (O2) stratosphere ~ 10 km troposphere temperature ozone inversion ~ 1 km Sunlight radicals Nitrogen oxides (NOx ≡ NO + NO2) Volatile organic compounds (VOCs) Ozone (O3) PM2.5 vehicles, industry, vegetation

PM2.5 and ozone air pollution are major environmental killers today Million environmental deaths per year worldwide (2010) OECD [2012]

Fine particulate matter (PM2.5) observed from satellite US air quality standard China air quality standard http://www.nasa.gov/topics/earth

A dismal Beijing day Agriculture (as NH3) Mean PM2.5 composition in Beijing [Huang et al., 2017] Agriculture (as NH3) Combustion, industry (partly as VOCs) Ammonium 12% Fuel combustion (as NOx) Nitrate 20% Organics 27% Combustion Mineral dust 17% Construction, soils Coal combustion (as SO2) ~50% is directly emitted (primary) ~50% is produced in atmosphere (secondary)

In 2013, the Chinese government initiated the “Clean Air Action” Scrubbing of emissions from coal combustion Bans on residential coal combustion Closing of polluting industries Emission standards for vehicles Bans on agricultural fires Encouragement of renewable energy sources

Clean Air Action has led to great improvement in PM2.5 air quality Annual mean PM2.5 at China Ministry of Ecology and Environment (MEE) sites 108 → 55 67 → 40 71 → 40 47 → 31 PM2.5 has decreased by 30-50% across urban China over 2013-2018 Zhai et al., 2019

Solvents Transportation Residential Industry Electricity Chinese emission inventory (MEIC) VOCs Primary emissions PM2.5 trends have been driven by controls on primary combustion emissions and SO2 Zheng et al. [2018]; Zhai et al. [2019]

Confirmation of Chinese emission trends by the NASA Aura satellite SO2 Aura satellite observations since 2004 NO2 Formaldehyde (VOC proxy) Wang et al., 2019; Shah et al., 2019; Shen et al., 2019 2005 2017

Unlike PM2.5, ozone pollution is getting worse Trends at the Ministry of Ecology and Environment sites PM2.5 ozone

Very severe ozone pollution problem in China Ozone is produced photochemically by VOCs in the presence of NOx US air quality standard China air quality standard Li et al. [2019a]

Decrease in PM2.5 pollution may be responsible for increase in ozone Sunlight H2O particles particles scavenge HO2 radicals that would otherwise produce ozone HO2 radicals Nitrogen oxides (NOx) Organics (VOCs) Ozone Model increase in ozone due to PM changes 2013-2017 decrease in PM2.5 increases radicals for ozone production Li et al. [2019a]

PM2.5 is more important than other factors in driving ozone increase GEOS-Chem simulation with MEIC (NOx, VOCs) and observed (PM2.5) trends: Simulated 2013-2017 changes in mean summer MDA8 ozone Increasing trend is mostly driven by decreasing PM2.5 Li et al., 2019a

Evidence of ozone suppression under high PM2.5 conditions Summertime relationship between ozone and PM2.5 in megacity clusters without PM2.5 with PM2.5 ozone suppression common influence of meteorology Ozone is depleted by 25 ppb at high PM2.5 Li et al., 2019b

Expected ozone change from Phase 2 of Clean Air Action Calls for 2018-2020 decreases of 8% for PM2.5, 9% for NOx, 10% for VOCs GEOS-Chem model simulation for North China Plain conditions Decreases of VOCs and NOx should (timidly!) reverse ozone increase Li et al., 2019b

Aggressive reduction of VOCs and NOx: an effective two-pollutant control strategy for China Observed 2014-2017 change in PM2.5 composition in Beijing Organic Sulfate Nitrate Ammonium Chloride Elemental carbon Decreasing NOx and VOCs will be necessary for further gains in PM2.5 H. Li et al., 2019

Effect of climate change on Beijing winter haze (high PM2.5) events

Meteorological conditions driving winter haze events: low wind speed (WS), low mixing depth (MLH), high relative humidity (RH) Cold front Chronology of observed haze event fog December 2016, local time High RH drives formation of sulfate and organics in the particle aqueous phase Wang et al., in prep.

Effect of 21st century climate change on wind speed and RH 2080-2099 vs. 2000-2019 differences in CMIP5 models for RCP8.5 scenario Change in meridional velocity Change in relative humidity at 850 hPa (V850) (RH) Decrease of RH over China is expected because of: Expansion of Hadley circulation Stronger warming over land than over oceans Shen et al. [2018]

Modeling the dependence of extreme haze events on meteorological variables Observed frequency distribution of wintertime 24-h PM2.5 in Beijing, 2009-2017 Apply extreme value theory to fit probability of extreme events to meteorological variables: point process model 95th percentile Best fit is to meridional wind velocity at 850 hPa (V850) and relative humidity (RH) Pendergrass et al., 2019

Extreme haze event probability as function of V850 and RH Green: observed 24-h PM2.5 > 300 μg m-3, 2009-2017 data Black: observed 24-h PM2.5 < 300 μg m-3 extreme haze regime Pendergrass et al., 2019

RCP8.5 future climate scenario Changes in (V850, RH) joint probability in CMIP5 models, 2051-2060 vs. 2006-2015 extreme haze regime RCP8.5 scenario shows no change for the (V850, RH) range leading to extreme events Pendergrass et al., 2019

RCP4.5 future climate scenario Changes in (V850, RH) joint probability in CMIP5 models, 2051-2060 vs. 2006-2015 extreme haze regime RCP4.5 shows decreased probability of the (V850, RH) range leading to extreme events RCP8.5 scenario shows no change for the (V850, RH) range leading to extreme events Pendergrass et al., 2019

Conclusions Fine particulate matter (PM2.5) in China has decreased by 30-50% from 2013 to 2018, largely because of controls on coal combustion Surface ozone pollution has increased during that period and this may largely be caused by decrease of PM2.5 that scavenges the radicals necessary for ozone production Controlling emissions of volatile organic compounds (VOCs) and nitrogen oxides (NOx) is an effective two-pollutant strategy to decrease both PM2.5 and ozone pollution in China Climate change is likely to decrease PM2.5 pollution in China through a decrease in relative humidity (RH)