1. 7th International DOAS Workshop
6-8 July 2015, Brussels
Study on distribution and transport of precursors SO2 and NO2 in North China Plain using mobile DOAS
Pinhua Xie, Ang Li, Fengcheng Wu, Zhaokun Hu,Fusheng Mou,
Jie Zhang, Hao Chen, Jin Xu, Jianguo Liu, Wenqing Liu
Anhui Institute of Optics and Fine Mechanics,
Chinese Academy of Sciences

2. Outline Introduction Mobile DOAS instruments Field Campaigns
- CAREBEIJING 2013
Results and Discussions
Summary

3. Introduction
China is facing with the regional and complex air pollution
2013/10/17－21 (XI’an)
2013/12/01－07 (YRD)
2014/02/19－26 (Beijing)
PM2.5
Number of days of haze
With the last 20 years very fast economy growing, now China is suffering severe air pollution problems, which is in regional and complex air pollution. Such as a large area of haze, this map shows that the number of days of haze in Chnia in most haze aera in east of China. Like JJJ, Yz, Pearl. Among them North China Plain is the most severe part. The annual average concentration of PM2.5 are much exceed the standard.
China was one of the quickest economically developing and urbanizing countries during the last 20 years with mega cities suffering on high air pollution levels. Jing-Jin-Ji area as one of the tree most developed area, the issues of air pollution become more and more serious, like sever haze. It has affected the health and life style of millions seriously, drawing extensive attention by China even national wide people.
>100

4. Introduction SO2, NO2 are important precursors of PM2.5
PM2.5 Chemical Compositions:
SO42- and NO3- contribute nearly 50% to PM2.5
WANG et al, 2014, SCIENCE CHINA
Many SO2 and NO2 sources locate in North China Plain, strongly affected the air quality of Beijing under specific wind field.
Wu et al., 2011, ACP
In order to know better about the sources and their influence to Beijing, it is necessary to investigate the spatial and temporal distribution of SO2 and NO2 in NCP.
Zhang et al., 2014, ACP
Su Fuqing et al, 2004

5. Introduction Mobile DOAS
Estimation of pollutant emissions from point sources or fugitive emission sources (such as: city, industrial area etc.)
Regional distributions of pollutants (SO2, NO2 etc. )
Transport process in combination with trajectory model
Validation of satellite data
Mobile DOAS was used to investigate the distribution of SO2 and NO2 VCDs, transport in in North China Plain (NCP).

6. Mobile DOAS instruments
Mobile DOAS Instrument (I)
-zenith observation
Mobile DOAS
△＜±0.1℃
Weather Station
Telescope
Temperature stabilizer
Our mobile DOAS system include:
Telescope: 80mm diameter and 170mm focal length, field of view about 0.1°
a UV/VIS detector spectrometer unit:
-Ocean Optics HR2000 spectrometer, spectral resolution 0.6nm, wavelength range: 290nm~420nm
- temperature stabilizer: precision ±0.1℃
GPS
miniature weather station: wind speed, wind direction, temperature, humidity, and pressure
DC +12V battery: +12V direct current is converted to AC by a power converter to power the entire system

7. Mobile DOAS instruments
Spectral Analysis –zenith observation
Reference spectra
Source
NO2
Vandaele, 298K (Io-correction using a SCD of 1e17 molec/cm²)
Vandaele, 220K
O3 deconvoluted
Bogumil, 223K (Io-correction using a SCD of 1e20 molec/cm²)
Bogumil, 243K (Io-correction using a SCD of 1e20 molec/cm²) O4
Hermans et al
HCHO
Meller
BrO
Fleischmann
Ring
calculated
Wavelength range nm
fit for NO2 and SO2 recorded at 13:04 on 12 June, 2013
Reference spectra
Source
SO2
Bogumil 293K, 2003
NO2
HCHO O3
Ring
calculated
Wavelength range nm
The spectrum in the “clean area” is chosen as the Frauenhofer reference spectrum which contains minimum concentration of SO2 and NO2. The reference spectrum can be corrected by MAX-DOAS if it is setup along the mobile DOAS measurement route,

8. Mobile DOAS instruments
Mobile DOAS Instrument (II)-Mobile MAX-DOAS
Mobile DOAS with Stabilized Platform
GPS antenna 1
GPS antenna 2
high precision turntable
attitude feedback
Obtained the absolute VCD
Detected more gas due to slant light-path absorption
aerosol and trace gas profile retrieval (dependence on experimental environment)
Gyroscope+GPSPID  Stabilized Platform
Specification:
Elevation angle: 90°, 20° (30°,15°….)
Spectral range: 290~420nm
Gas: SO2, NO2, O4, HCHO, BrO,….
Precision of gyroscope: 0.1°, azimuth angle: 0.5°, elevation angle: 0.3°.

9. Field Campaigns 5 1 4 3 2 CAREBEIJING 2013 field campaign Beijing
Shijiazhuang
Baoding
Jinan
Dezhou
Cangzhou
Tianjin
Zhuozhou
China 5 1 4 3
Routes：
5 routes  1 cycle
—Beijing-Shijiazhuang
—Shijiazhuang-Dezhou
—Dezhou-Baoding-Cangzhou
—Cangzhou-Zhuozhou
—Zhuozhou-Beijing
10:00-14:00
—Stable boundary layer
— battery endurance
June 11th-July 16th , 2013
All routes are expressways
NCP is located in northern China, surrounding by Taihang mountains (at the west of NCP), Yanshan mountains (at the north of NCP) and Bohai sea (at the east of NCP). 2

10. The mobile platform also equipped some point instruments, like gaseous analyzers (SO2, NOx, CO etc.) and aerosol instruments (PM2.5, PM10 etc.)
Inlet system
Inner vehicle
Our mobile DOAS system is installed on a diesel vehicle from PKU. This mobile platform also equipped some point isntruments...
The data were chosen from good weather condition, clear sky and cloudy with cold fration less than 0.4
Roof of vehicle
Wind:
southerly wind (11 Jun~15 Jun, 24 Jun~26 Jun),
northerly wind (17 Jun~21 Jun, 2 Jul~ 7Jul)
Weather condition: clear or cloudy
Cloud Fraction≤0.4：11 Jun~13 Jun，18 Jun，25 Jun~26 Jun，3 Jul，6 Jul， total 8 days

11. Results and Discussions
CAREBEIJING 2013 field campaign
Distributions of SO2 and NO2 VCD over NCP
- Distributions over whole NCP
- Spatial and temporal different routes (southwest route and southeast different wind field (south and north)
Validation of OMI NO2
During the 2013 field campaign, the following results can be discussed...

12. Results and Discussions
Distributions of SO2 and NO2 VCD over NCP
Distributions over whole NCP
Southerly wind
11 Jun.~15 Jun.
11 Jun.~15 Jun.
Shijiazhuang
JiNan
Tianjin
Beijing
NO2
Shijiazhuang
JiNan
Tianjin
Beijing
SO2
The VCDs of SO2 and NO2 are affected by the cities. The VCDs increase near the cities.
Some hot spots are found, like close to JiNan
Serious air pollution in Hebei(southwest route). The VCD over southwest region is higher than those over southeast.

13. Results and Discussions
Distributions of SO2 and NO2 VCD over NCP
Distributions over whole NCP
Northerly wind
17 Jun.~21 Jun.
17 Jun.~21 Jun.
Shijiazhuang
JiNan
Tianjin
Beijing
SO2
Shijiazhuang
JiNan
Tianjin
Beijing
NO2
The VCDs of SO2 and NO2 reduce under northerly wind.
The hot spot near the Ji’Nan disappear under the northerly wind.

14. Results and Discussions
Distributions of SO2 and NO2 VCD over NCP
Spatial and temporal southwest and southeast measurement route
Beijing
Southwest measurement route:
Beijing-Baoding-Shijiazhuang
Southerly wind: 6.11, 6.24
Northerly wind: 6.17, 7.2
Tianjin
Baoding
Southeast measurement route:
Dezhou-Tianjin-Beijing
Southerly wind:
6.13, 6.14, 6.26,7.4, 7.6
Northerly wind: 6.20
Shijiazhuang
Dezhou

15. Results and Discussions
Distributions of SO2 and NO2 VCD over NCP
Spatial and temporal southwest measurement route
SO2 VCD (mobile DOAS)
SO2 surface concentration
The SO2 VCD and near-surface concentration under southerly wind are 2.60 and 1.24 times of that under northerly wind, respectively. The SO2 VCDs have a distinct variations under southerly and northerly wind. It shows high elevated point sources along the southwest route.
According to the “Box-chart”, the peak value indicates the elevated sources exist along the southwest measurement route.
The upper layer SO2 existed, which can be transported to Beijing.
We use the box- chart statistic calculation the data along the route on different days with south or north wind
6.24
6.11
6.17
7.2

16. Results and Discussions
Distributions of SO2 and NO2 VCD over NCP
Spatial and temporal southwest measurement route
NO2 VCD from mobile DOAS
NO2 concentration from point instrument
The difference of NO2 VCD for southerly and northerly wind is lower than SO2.
NO2 mainly located near surface.

17. Results and Discussions
Distributions of SO2 and NO2 VCD over NCP
Spatial and temporal southwest measurement route
石家庄
Southerly wind
SO2
Northerly wind
SO2
Beijing
Beijing
Beijing
Beijing
Shijiazhuang
Shijiazhuang
Shijiazhuang
Shijiazhuang
6.11
6.24
6.17
7.2
Southwest route is a transport route. The air quality of Beijing is affected by the transport from southern area.

18. Results and Discussions
Distributions of SO2 and NO2 VCD over NCP
Spatial and temporal southeast measurement route
SO2 VCD from mobile DOAS
SO2 surface concentration
Low scatted sources in the southeast route.

19. Results and Discussions
Distributions of SO2 and NO2 VCD over NCP
Spatial and temporal southeast measurement route
NO2 VCD from mobile DOAS
NO2 concentration from point instrument
NO2 mainly located near surface, from traffic

20. Results and Discussions
Distributions of SO2 and NO2 VCD over NCP
Spatial and temporal southeast measurement route
southwest route
southeast route
High emissions in the southwest is in accordance with our observation (left figure).
Elevated sources are the major contributors to SO2 along southwest measurement route.
Southwest measurement route is a transport route for Beijing.
Low area sources are the contributors to SO2 along southeast measurement route
Spatial distributions of anthropogenic SO2 in and around
Beijing with horizontal resolution of 12 by 12 km2
cited by Wang et al., ACP, 2014

21. Results and Discussions
2. Validation of OMI NO2
Cloud fraction ≤0.4
Grid resolution= 0.1
Jun 11, 12, 13, 18, 25, 26, July 3 and July 6 total 8 days

22. Results and Discussions
2. Validation of OMI NO2
Mobile DOAS and OMI can capture the high and low value simultaneously.

23. Results and Discussions
3. Validation of OMI NO2
The both datasets have a good agreement, with correlation coefficient R2=0.65.

24. HOPE J3A 2014 field campaign —Beijing 5th Ring Road (98.58km)
Routes：
Two cycle
—Beijing 5th Ring Road (98.58km)
—Beijing 6th Ring Road (192km）
10:00-14:00
November 3th 2014 – January 12th 2015
Weather condition: clear or cloudy
Dominated Wind field: north

25. Dominant wind direction
Observation of NO2 distribution and emission flux during APEC
Data
Dominant wind direction
Wind speed
Emission of
NO2
03/11/2014
south-west (260°)
1 m/s
0.59 kg/s
05/11/2014
north-west (280°)
1.1 m/s
0.51 kg/s
07/11/2014
south (90°)
1.3m/s
1.01 kg/s
21/12/2014
west (270°)
7 m/s
2.47 kg/s
27/12/2014
north-west (320°)
2 m/s
1.34 kg/s
31/12/2014
2.17 kg/s
APEC
A decrease in NO2 emission during the APEC, which caused by the strict control policies.

26. Results and Discussions
Identification of emission Beijing 5th and 6th Ring Road
HOPE J3A 2014 field campaign
NO2 VCD（ppmm）
2014年12月21日
NO2
2014年11月3日
SO2
2014年11月7日
2014年12月31日
NO2
NO2
NO2
NO2
Beijing 6th Ring Road
NO2
NO2
NO2
Beijing 6th Ring Road
The vehicle exhaust is the major source of NO2 in Beijing.
The distribution of NO2 VCD of western 6th ring road is affected by the industrial source near Mentougou Area, which resulted in local NO2 VCD increase.

27. Summary
In NCP, the SO2 and NO2 VCDs are higher along the southwest route than that along southeast route. However, the near-surface concentrations are higher along southeast route.
Southwest route is a important transport pathway to affect air quality in Beijing. High elevated point sources are the major contributors to SO2 along southwest route. Low area sources are the contributors to SO2 along southeast route.
Vehicle emission is main source of NO2. The SO2 and NO2 VCD enhance simultaneously indicates there is coal-combustion source.
In Beijing City, SO2 is most transported from surrounding area whereas the NO2 is from local traffic.
There is a good agreement between OMI and mobile DOAS. The correlation coefficient is R2=0.65.
Mobile DOAS is a potential powerful tool for pollutant distribution investigation , tracking the plume as well as satellite validation. .

28. Case: “Tracking Haze” experimental observation(11 Oct.~18 Oct., 2014 )
Hefei-Zhengzhou-Wuhan-Hefei-JiNan
The distributions of SO2 and NO2 are characterized by mobile DOAS rapidly.
The SO2 and NO2 VCD was greatly influenced by the heavy industrial source emission. The emission sources are identified using this scanning measurement, like heavy emission sources are found in Wuhan.

29. Thank you for your attention!
Acknowledgements:
We would like to thank Prof. Zhu’s group (Peking University) for arrangement of the experiments and providing the data from point instruments during the CAREBEIJING 2013 field campaign.
Anhui Institute of Optics & Fine Mechanics,
Chinese Academy of Sciences