1. 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

2. The industrial revolution and air pollution
Pittsburgh in the 1940s

3. 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

4. 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

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

6. Fine particulate matter (PM2.5) observed from satellite
US air quality standard China air quality standard

7. 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)

8. 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

9. 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
Zhai et al., 2019

10. 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]

11. 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

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

13. 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]

14. 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
decrease in PM2.5
increases radicals for ozone production
Li et al. [2019a]

15. 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 changes in mean summer MDA8 ozone
Increasing trend is mostly driven by decreasing PM2.5
Li et al., 2019a

16. 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

17. Expected ozone change from Phase 2 of Clean Air Action
Calls for 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

18. Aggressive reduction of VOCs and NOx: an effective two-pollutant control strategy for China
Observed 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

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

20. 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.

21. Effect of 21st century climate change on wind speed and RH
vs 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]

22. Modeling the dependence of extreme haze events on meteorological variables
Observed frequency distribution of wintertime 24-h PM2.5 in Beijing,
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

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

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

25. RCP4.5 future climate scenario
Changes in (V850, RH) joint probability in CMIP5 models, vs
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

26. 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)