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1. Fine particulate matter and ozone pollution in China:
recent trends, future controls, and impact of climate change
Daniel J. Jacob
Shixian Zhai Ke Li
Lu Shen
Viral Shah
A typical day in Beijing (2030)
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
Coal combustion
Temperature
Altitude
inversion
sulfate
soot
particles
(PM2.5)
< 1km
Sulfur dioxide (SO2)

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

5. PM2.5 and ozone air pollution are major environmental killers today
OECD [2012]
0
0.5
1
1.5
2
2.5
PM2.5 ozone water supply indoor air malaria
Million environmental deaths per year worldwide (2010)

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

7. A dismal Beijing day
Black carbon
8%
Sulfate
16%
Organics 27%
Combustion, industry
(partly as VOCs)
Combustion
Mineral dust
17%
Construction, soils
Coal combustion
(as SO2)
Nitrate
20%
Fuel combustion
(as NOx)
Ammonium
12%
Agriculture
(as NH3)
Mean PM2.5 composition in Beijing
[Huang et al., 2017]
~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
Zhai et al., 2019
PM2.5 has decreased by 30-50% across urban China over 2013-2018
108 → 55
67 → 40
47 → 31
71 → 40

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

11. Confirmation of Chinese emission trends by the NASA Aura satellite
Aura satellite observations since 2004
2005 2017
SO2
Formaldehyde
(VOC proxy)
NO2
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
Li et al. [2019a]
China
air quality
standard
US
air quality
standard
Ozone is produced photochemically by VOCs in the presence of NOx

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

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

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

17. 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

18. 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

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)
0
5
0
0
0
0
0
20
10
0
SO
2
(ppb)
4
2
0
10
5
0
HONO
(ppb)
40
20
NH
3
(ppb
0
0
0
100
50
0
NO
2
(ppb)
80
40
0
RH
(%)
4
2
0
1200
600
0
MLH
(m.A.G.L.)
a
b
c
d
e
f
Stage I Stage II
0
5
0
0
0
0
5
0
0
0
0
20
10
0
SO
2
(ppb)
400
200
0
PM
2.5
(µg
m
-3
)
4
2
0
10
5
0
HONO
(ppb)
40
20
0
NH
3
(ppb)
0
0
0
100
50
0
NO
2
(ppb)
80
40
0
RH
(%)
4
2
0
1200
600
0
MLH
(m.A.G.L.)
a
b
c
d
e
f
g
Stage I Stage II
16 17 18 19 20 21 22
4 5
ate
December 2016, local time, UTC+8
0
5
0
0
0
0
5
0
0
0
0
20
10
0
SO
2
(ppb)
400
200
0
PM
2.5
(µg
m
-3
)
4
2
0
10
5
0
HONO
(ppb)
40
20
0
NH
3
(ppb)
0
0
0
100
50
0
NO
2
(ppb)
80
40
0
RH
(%)
0 0
L.)
b
c
d
e
f
g
16 17 18 19 20 21 22
4 5
te
December 2016, local time, UTC+8
30
15
0
O
3
(ppb)
330
320
N
2
O
(ppb)
30
15
0
BC
(µg
m
-3
)
60
30
0
Sulfate
(µg
m
-3
)
20
10
0
(ppb)
400
200
0
(µg
m
-3
)
0.4
0.2
0.0
LWC
(g
m
-3
) 10
5
0
(ppb)
40
20
0
(ppb)
60
30
0
Nitrate
(µg
m
-3
)
100
50
0
(ppb)
80
40
0
0 0
L.)
b
c
d
e
f
g
16 17 18 19 20 21 22
4 5
Date
December 2016, local time, UTC+8
30
15
0
O
3
(ppb)
330
320
N
2
O
(ppb)
30
15
0
BC
(µg
m
-3
)
60
30
0
Sulfate
(µg
m
-3
)
20
10
0
(ppb)
400
200
0
(µg
m
-3
)
0.4
0.2
0.0
LWC
(g
m
-3
)
10
5
0
(ppb)
40
20
0
(ppb)
60
30
0
Nitrate
(µg
m
-3
)
100
50
0
(ppb)
80
40
0
4
2
0
WS
(m
s
-1
)
1200
600
0
(m.A.G.L.)
a
b
c
d
e
f
g
16 17 18 19 20 21 22
4 5
Date
December 2016, local time, UTC+8
30
15
O
3
(ppb)
330
320
N
2
O
(ppb)
60
30
0
Sulfate
(µg
m
-3
)
20
10
0
(ppb)
0.4
0.2
0.0
LWC
(g
m
-3
)
10
5
0
(ppb)
40
20
(ppb)
60
30
0
Nitrate
(µg
m
-3
)
100
50
0
(ppb)
80
40
0
4
2
0
WS
(m
s
-1
)
1200
600
0
(m.A.G.L.)
a
b
c
d
e
f
Stage I Stage II
December 2016, local time
Chronology of observed haze event
fog
Cold front
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
2080-2099 vs. 2000-2019 differences in CMIP5 models for RCP8.5 scenario
Shen et al. [2018]
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

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

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

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

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