Fine particulate matter and ozone pollution in China

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) Shixian Zhai Viral Shah Lu Shen Ke Li Junfeng Wang Drew Pendergrass

The industrial revolution and air pollution Pittsburgh in the 1940 s

London fog: first evidence of air pollution deaths Fine particulate matter (PM 2. 5) from domestic+industrial combustion “Killer fog” of December 1952 caused 10, 000 deaths in 4 days Altitude inversion < 1 km Temperature Sulfur dioxide (SO 2) Coal combustion particles (PM 2. 5) sulfate soot

Los Angeles smog: first evidence of ozone air pollution Respiratory problems, vegetation damage due to high surface ozone altitude produced by photolysis of oxygen (O 2) stratosphere ~ 10 km troposphere ozone ~ 1 km temperature inversion Sunlight Nitrogen oxides (NOx ≡ NO + NO 2) radicals Volatile organic compounds (VOCs) vehicles, industry, vegetation Ozone (O 3) PM 2. 5

PM 2. 5 and ozone air pollution are major environmental killers today Million environmental deaths per year worldwide (2010) 2. 5 2 1. 5 1 0. 5 0 PM 2. 5 ozone water supply indoor air malaria OECD [2012]

Fine particulate matter (PM 2. 5) observed from satellite US air quality standard China air quality standard http: //www. nasa. gov/topics/earth

A dismal Beijing day Mean PM 2. 5 composition in Beijing [Huang et al. , 2017] Agriculture (as NH 3) Fuel combustion (as NOx) Ammonium 12% Nitrate 20% Sulfate 16% Coal combustion (as SO 2) Combustion, industry (partly as VOCs) Organics 27% Black carbon 8% Mineral dust 17% Combustion Construction, soils ~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 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 PM 2. 5 air quality Annual mean PM 2. 5 at China Ministry of Ecology and Environment (MEE) sites 108 → 55 67 → 40 71 → 40 47 → 31 PM 2. 5 has decreased by 30 -50% across urban China over 2013 -2018 Zhai et al. , 2019

Chinese emission inventory (MEIC) PM 2. 5 trends have been driven by controls on primary combustion emissions and SO 2 Solvents Transportation Residential Industry Electricity Zheng et al. [2018]; Zhai et al. [2019] Primary emissions VOCs

Confirmation of Chinese emission trends by the NASA Aura satellite SO 2 Aura satellite observations since 2004 NO 2 Formaldehyde (VOC proxy) Wang et al. , 2019; Shah et al. , 2019; Shen et al. , 2019 2005 2017

Unlike PM 2. 5, ozone pollution is getting worse Trends at the Ministry of Ecology and Environment sites PM 2. 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. [2019 a]

Decrease in PM 2. 5 pollution may be responsible for increase in ozone Sunlight H 2 O particles scavenge HO 2 radicals that would otherwise produce ozone particles HO 2 radicals Nitrogen oxides (NOx) Organics (VOCs) Ozone Model increase in ozone due to PM changes 2013 -2017 decrease in PM 2. 5 increases radicals for ozone production Li et al. [2019 a]

PM 2. 5 is more important than other factors in driving ozone increase GEOS-Chem simulation with MEIC (NOx, VOCs) and observed (PM 2. 5) trends: Simulated 2013 -2017 changes in mean summer MDA 8 ozone Increasing trend is mostly driven by decreasing PM 2. 5 Li et al. , 2019 a

Evidence of ozone suppression under high PM 2. 5 conditions Summertime relationship between ozone and PM 2. 5 in megacity clusters without PM 2. 5 with PM 2. 5 ozone suppression common influence of meteorology Ozone is depleted by 25 ppb at high PM 2. 5 Li et al. , 2019 b

Expected ozone change from Phase 2 of Clean Air Action Calls for 2018 -2020 decreases of 8% for PM 2. 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. , 2019 b

Aggressive reduction of VOCs and NOx: an effective two-pollutant control strategy for China Observed 2014 -2017 change in PM 2. 5 composition in Beijing Organic Sulfate Nitrate Ammonium Chloride Elemental carbon Decreasing NOx and VOCs will be necessary for further gains in PM 2. 5 H. Li et al. , 2019

Effect of climate change on Beijing winter haze (high PM 2. 5) events

Meteorological conditions driving winter haze events: low wind speed (WS), low mixing depth (MLH), high relative humidity (RH) Chronology of observed haze event Cold front 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 21 st century climate change on wind speed and RH 2080 -2099 vs. 2000 -2019 differences in CMIP 5 models for RCP 8. 5 scenario Change in meridional velocity at 850 h. Pa (V 850) Change in relative humidity (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 PM 2. 5 in Beijing, 2009 -2017 Apply extreme value theory to fit probability of extreme events to meteorological variables: point process model 95 th percentile Best fit is to meridional wind velocity at 850 h. Pa (V 850) and relative humidity (RH) Pendergrass et al. , 2019

Extreme haze event probability as function of V 850 and RH Green: observed 24 -h PM 2. 5 > 300 μg m-3, 2009 -2017 data Black: observed 24 -h PM 2. 5 < 300 μg m-3 extreme haze regime Pendergrass et al. , 2019

RCP 8. 5 future climate scenario Changes in (V 850, RH) joint probability in CMIP 5 models, 2051 -2060 vs. 2006 -2015 extreme haze regime RCP 8. 5 scenario shows no change for the (V 850, RH) range leading to extreme events Pendergrass et al. , 2019

RCP 4. 5 future climate scenario Changes in (V 850, RH) joint probability in CMIP 5 models, 2051 -2060 vs. 2006 -2015 extreme haze regime RCP 4. 5 decreased the(V 850, RH) RH)rangeleadingtotoextremeevents RCP 8. 5 shows scenario shows noprobability change forofthe Pendergrass et al. , 2019

Conclusions • Fine particulate matter (PM 2. 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 PM 2. 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 PM 2. 5 and ozone pollution in China • Climate change is likely to decrease PM 2. 5 pollution in China through a decrease in relative humidity (RH)