controlling particulate nitrate pollution in...
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Controlling particulate nitrate pollution in China
Shixian Zhai
with Daniel J. Jacob*, Xuan Wang, Viral Shah, Ke Li, Jonathan Moch, Kelvin H. Bates, Shaojie Song, Lu Shen, and Yuzhong Zhang from Harvard University
Zirui Liu, Tianxue Wen, and Yele Sun, IAP/CAS; Gan Luo and Fangqun Yu, U. at Albany; Litao Wang and Mengyao Qi, Hebei U. of Engineering; Jun Tao, Jinan U.; Ke Gui, CAMS; Honghui Xu, Zhejiang Institute of Meteorological Sciences; Qiang Zhang, Tsinghua U.; Hyun Chul Lee and Hyoungwoo Choi, Samsung; Tianliang Zhao and Hong Liao, NUIST.
AGU FALL MEETING 2020: A172-06
LIVE Q&A: Tuesday, 15 December 2020, 04:00 – 05:00 PST
Funding: JLAQC and SAMSUNG
China’s rigorous Clean Air Action has greatly improved its PM2.5 air quality
Zheng et al., ACP, 2018
MEIC emission inventory
Zhai et al., ACP, 2019
2013 2018
Observed annual mean PM2.5
30~50%108 → 55
67 → 40
47 → 3171 → 40
Air quality standard:35μg m-3(Phase I), 10μg m-3(WHO).
China Clean Air action
↓59%
↓33%↓23%↓21%
BC: ↓28%OC: ↓32%
NitrateSulfateAmmoniumOABCChlorineOthers
2011
2012
2013
2014
2015
2016
2017
2018
Concentration, µg m-3
Observations in winter & autumn at Beijing
Particulate nitrate didn’t decrease with the decrease of NOx emissions
From National Air Pollution Prevention and Control Center (provided by PKU)
120
80
40
40
40
40
0
Percentage
2011
2012
2013
2014
2015
2016
2017
2018
0%
30%
60%
90%40
40
40
40
Tota
l PM
2.5
PM1
nitra
te
2014-2015 2016-2017 2017-2018 2018-2019a
b
Mean observed: 90 μg m-3
Model: 71 μg m-310078
4238
5257
Mean observed: 9 μg m-3
Model: 7 μg m-31810
55
109
μg m-3
Mass ratio of
PM1 nitrate / total PM
2.5
Particulate nitrate on winter haze days has increasedBeijing wintertime data: nitrate is now the most important component of PM2.5
Observation data are provided by Yele Sun from IAP/CASZhai et al., submitted
Standard simulation Fixed meteorology
Nitrate in winter would have increased were it not for favorable meteorologyNitrate under winter haze conditions increased by > 30%
Chemical drivers of particulate nitrate trends:
Model results overNorth China Plain
Zhai et al., submitted
Faster conversion from NOx to nitrate
NO3T
Nonlinearity:
NOx-limited: NOx ↓à HOx ↓à NOx lifetime ↑(slower NOx to nitrate)
NOx-saturated: NOx ↓à HOx ↑à NOx lifetime ↓(faster NOx to nitrate)
Diagram for nitrate production
Faster NOx to nitrate conversion rate in winter.
(shorter NOx lifetime)
Shah et al., ACP, 2019
NOx trends over China
NO3T = NO3
- + HNO3
Daytime
Nighttime
(from Viral Shah)
Faster conversion from NOx to nitrate is insufficient to explain the increase of nitrate under winter haze conditions
Winter hazeWinterSummer
NOx lifetime, hours NO3T production, µg m-3 hr-1
Zhai et al., submitted
Increase in NO3T lifetime against deposition is the dominant factor
explaining the lack response of nitrate to NOx emission controlsThe lifetime of NO3
T is controlled by the small fraction present as HNO3(g).
[NO3-]/[NO3
T] ratio NO3T lifetime, hours
SO2 ↓ NH3 ↑NO3
- HNO3(g)
Surface
x10 ≈Slow Fast
deposition
Vice versa: decreasing NH3 emissions should be able to decrease NO3
T total nitrate lifetime.Zhai et al., submitted
In large excess
NH3 is the most effective lever for PM2.5 nitrate controlResponse of particulate nitrate
to emission controls
Zhai et al., submitted
Ø Reducing NH3 emissions by any increment is beneficial.
Ø Reducing NOx emissions drives a decrease in NOx lifetime which offsets the decrease in NO3
T
production.
SO2 NOx VOCs NH3NOx + VOCs + NH3
Conclusions
1. Stringent emission controls have decreased PM2.5 concentrations in China by 30-50% over the 2013-2018 period.
2. Particulate nitrate has not responded effectively to emission controls on NOx, and has increased during winter haze pollution events in the North China Plain.
3. The dominant factor driving the observed nitrate trends is the increase in NO3T
lifetime against deposition as the particulate fraction of NO3T approaches unity.
4. Decreasing wintertime ammonia emissions would be most effective for decreasing particulate nitrate in China.
Welcome to my LIVE Q&A SESSION: A172-06 Tuesday, 15 December 2020, 04:00 – 05:00 PST
Contact: Shixian Zhai ([email protected])