The effect of emission control measures on ozone concentration The 9th International GEOS-Chem Meeting (IGC9) The effect of emission control measures on ozone concentration in Hangzhou during G20 meeting in 2016 Ye Wang & Hong Liao* School of Environmental Science and Engineering, Nanjing University of Information Science & Technology Good afternoon, everyone. I am Ye Wang, from NUIST. My advisor is pro. Hong Liao. And the topic of my presentation is … I am going to start with the current status of O3 pollution in China.

Current status of O3 pollution in China With the effective reduction of PM2.5 in past several years, O3 concentration increased sharply in most regions of China. Under the background of increasingly serious ozone pollution, emission reduction during G20 in 2016 provided us a typical opportunity to study if control measures could decrease ozone concentration effectively in summer. We’ll now move on to the observed air pollutants in Hangzhou during G20 under emission control. Ke Li et al., PNAS, 2018 National standard: MDA8 O3 > 160 μg m-3 (≈ 80 ppbv)

Observed air pollutants in Hangzhou during G20 under emission control Before G20 During G20 After G20 The blue dashed lines represent national standards for pollutants. It is obvious that all pollutants, except for o3, were below national standards during G20. And the mean value of MDA8 o3 during g20 was up to 160 micrograms per cubic meter. But the trend of MDA8 O3 was continuous downward. So the scientific questions are as follows: G20: 4-5 September, 2016 Period of emission control: 24 August to 6 September, 2016

Scientific questions Did emission control measures carried out during G20 reduced O3 effectively? Is it necessary to implement district-joint control measures? How sensitive is O3 concentration to emission reductions in different sectors?

Emission reductions in YRD during G20 Areas in YRD under emission control YRD CA(YRD) CA (ZJ) SCA CRA CRA: Core area SCA: Strictly controlled area CA (ZJ): Controlled area in Zhejing province CA (YRD): Controlled area in YRD Emission reductions by sectors during G20 Periods Sectors CRA SCA CA (ZJ) CA (YRD) Emission Reduction NOx (kt) VOC (ktC) VOC (ktC) 8/24-8/27 Industry 1.37 2.43 100% 1.64 2.83 50% 0.87 1.56 10.58 10.63 40% Power 0.54 0.003 1.35 0.01 30% 0.50 7.50 0.04 Residential 0.02 0.17 0.03 0.24 0.19 0.41 2.14 0%  Transport 0.98 0.66 0 % 1.46 0.91 0.90 0.58  0% 10.96 3.38 0% 8/28-9/6 3.53 5.03 4.24 5.86 2.26 3.23 27.81 22.29 1.15 2.89 1.09 16.61 0.08 0.35 0.07 0.49 0.06 0.38 1.03 4.30 2.50 1.28 3.72 1.78 2.30 1.12 27.94 6.86 According to the environmental quality guarantee scheme issued by government in 2016, areas in Yangtze River delta were divided into four parts and they are… emission reductions by sectors are described in this table. The emissions in different regions were calculated by MEIC inventory in 2016. ——Environmental Quality Guarantee Scheme, 2016.

Nested simulation over Asia Numerical experiments GEOS-Chem simulation Nested simulation over Asia Numerical experiments Version: v11-01 MET: MERRA2 Spatial resolution: 0.5°x0.625° Vertial resolution: 72 levels Resolution: 0.5°x0.625° Emission: MEIC_2016 Time: 8 August-30 September To quantify the necessity of district-joint control measures CTRLCRA CTRLZJ CTRLYRD To quantify how sensitive is O3 concentration to emission reductions in different sectors The version of GEOS-Chem model we used is 11.01, meteorological field is MERRA2 and emission inventory is MEIC in 2016. To quantify the necessity of district-joint control measures, we designed three numerical experiments and areas in CTRLZJ experiment are core area, strictly controlled area, controlled area in zj province. And ctrlYRD experiment includes all control areas. Four numerical experiments were designed to quantify how sensitive is O3 concentration to emission reductions in different sectors. And all emissions were cut down in them. CA(YRD) CTRLIND CTRLPOW CTRLRES CTRLTRA CRA SCA CA (ZJ)

Model evaluation: MDA8 O3 Observation Simulation Comparison of MDA8 O3 in Hangzhou between obs. and sim. NMB: Before G20: 21.7% During G20: 6.1% After G20: 25.0% Comparison of distribution of MDA8 O3 8 Aug. 6 Sep. Comparison of MDA8_O3 between observation and simulation in Base case were conducted to evaluate model performance. There are good agreements between simulated and observed data. Dots: observed values Contour: simulated values

Results: the effect of emission controls on O3 during G20 Comparison of MDA8_O3 in Hangzhou among OBS., BASE and CTRLYRD OBS BASE CTRLYRD CTRLYRD-BASE CTRLYRD-BASE (Percentage) Now we will move on to the results. Comparison of MDA8_O3 during G20 in Hangzhou among observation, base case and CTRLYRD experiment is shown in this picture. CTRLYRD is the actual strategy applied during G20. we can find that the values of MDA8 O3 simulated in CTRLYRD are much lower than that in base case. The mean difference of MDA8_O3 in Hangzhou between CTRLYRD experiment and base case is minus twenty one micrograms per cubic meter. Therefore, the control measures reduced O3 concentration in Hangzhou effectively. Mean difference of MDA8 O3 in Hangzhou: -21.0 μg m-3 (-11.6%) μg m-3

Results: impact of area and district-joint control on O3 during G20 BASE Reduction (Experiments-BASE) in MDA8 O3 in Hangzhou during G20: CTRLCRA (Controlling core area): -12.5 μg m-3 CTRLZJ (Controlling Zhejiang province): -16.1 μg m-3 CTRLYRD (Controlling Yangtze River Delta): -21.0 μg m-3 Difference in MDA8 O3 during G20 from control measures CTRLCRA-CTRL CTRLCRA-CTRL CTRLCRA-CTRL Let’s see the impact of area and district-joint control on O3 during G20. Comparing the reduction in MDA8 O3 in Hangzhou, it is obvious that controlling core area, Zhejiang province and Yangtze River delta could all decrease O3 concentration in Hangzhou effectively. However, controlling YRD is most effective. The distribution of absolute difference of MDA8_O3 shows the same conclusion. So it is necessary to carry out district-joint measures during G20. CA(YRD) CRA SCA CA(ZJ) μg m-3

Results: Why did O3 concentration decrease so effectively? VOCs/NOx (Base) NOx: NO+NO2 VOCs: C2H6+C3H8+ALK4+PRPE+ACET+MEK+ISOP VOCs/NOx>15: NOx-limited zone VOCs/NOx<4 : VOC-limited zone 4≤VOCs/NOx≤15: transition zone Carrillotorres et al., 2017 The ratios of VOCs to Nox in base case can explain why measures during G20 reduced ozone concentration so effectively. The reason is that … Core area and most of Zhejiang province were in transition zone; reductions in either NOx or VOCs reduce O3

Results: impact of emission reductions by sectors on O3 CTRLIND-BASE CTRLPOW-BASE Mean reductions of MDA8 O3 in Hangzhou during G20: CTRLIND: 18.85 μg m-3 CTRLPOW: 5.25 μg m-3 CTRLTRA: 12.98 μg m-3 CTRLRES: 3.14 μg m-3 CTRLTRA-BASE CTRLRES-BASE More emission reductions should be made to keep O3 below national standard during the meeting. So how sensitive is O3 concentration to emission reductions in different sectors? Mean reductions of MDA8 O3 in Hangzhou in each experiments are shown here. So controlling any sector could reduce O3 concentration when industrial emission control is most effective following by traffic emission control. It is suggested that the intensity of industrial and traffic emission control could be improved to achieve the standard.

Summary The mean difference of simulated MDA8 O3 in Hangzhou between Base and CTRLYRD during G20 is -21.0 μg m-3 (-11.6%). The control measures reduced O3 in Hangzhou effectively during G20. Comparing mean reduction of MDA8 O3 in Hangzhou during G20 in CTRLCRA, CTRLZJ and CTRLYRD, it is necessary to carry out district-joint emission control measures during G20. Comparing mean reduction of MDA8 O3 in Hangzhou during G20 in CTRLIND, CTRLPOW, CTRLRES and CTRLTRA, the intensity of industrial and traffic emission control could be improved to keep O3 below national standards. Here is my brief summary. So that’s all, thank you very much.

THANK YOU