Observation-based sources evolution of non-methane hydrocarbons (NMHCs) in a megacity of China.

Both concentrations and emissions of many air pollutants have been decreasing due to implement of control measures in China, in contrast to the fact that an increase in emissions of non-methane hydrocarbons (NMHCs) has been reported. This study employed seven years continuous NMHCs measurements and the related activities data of Shanghai, a megacity in China, to explore evolution of emissions and effectiveness of air pollution control measures. The mixing ratio of NMHCs showed no statistical interannual changes, of which their compositions exhibited marked changes. This resulted in a decreasing trend of ozone formation potential by 3.8%/year (p < 0.05, the same below), which should be beneficial to ozone pollution mitigation as its production in Shanghai is in the NMHCs-limited regime. Observed alkanes, aromatics and acetylene changed by +3.7%/year, -5.9%/year and -7.4%/year, respectively, and alkenes showed no apparent trend. NMHCs sources were apportioned by a positive matrix factorization model. Accordingly, vehicular emissions (-5.9%/year) and petrochemical industry emissions (-7.1%/year) decreased significantly, but the decrease slowed down; significant reduction in solvent usage (-9.0%/year) appeared after 2010; however, emissions of natural gas (+12.6%/year) and fuel evaporation (with an increasing fraction) became more important. The inconsistency between observations and inventories was found in interannual trend and speciation as well as source contributions, emphasizing the need for further validation in NMHCs emission inventory. Our study confirms the effectiveness of measures targeting mobile and centralized emissions from industrial sources and reveals a need focusing on fugitive emissions, which provided new insights into future air policies in polluted region.

[Characteristics and Control Strategies on Summertime Peak Ozone Concentration in Shanghai].

With the continuous development of air pollution control measures, the concentration of PM2.5 in Shanghai has shown a conspicuous downward trend in recent years. However, frequent O3 pollution events have highlighted the urgent need to explore the occurrence patterns of O3 pollution and develop scientific strategies for reducing O3 peaks. This study examines data from July 2017, when the cumulative number of O3 pollution days in 17 cities in the Yangtze River Delta was 165 days, of which Shanghai was the most serious, with an exceedance rate of 64.5%. During this period, the average concentration of NO2 in Shanghai was 27.1 µg·m-3 and volatile organic copunds (VOCs) mixing ratio was 22.5×10-9. By analyzing ozone precursor concentrations and meteorological factors, we determined that these events mainly resulted from a combination of unfavorable meteorological conditions such as high temperature, low humidity, low wind speed, and high precursor emissions. WRF-CMAQ scenario simulations showed that a reduction in precursor emissions in Shanghai alone would have a limited controlling effect on regional O3 pollution. Thus, regional joint control is recommended when widespread pollution events occur. Our analysis shows that if VOCs in Shanghai and nine neighboring cities can be reduced by 30%, the maximum 8-h O3 concentration in Shanghai could be reduced by 7.2%. If the reduction number of these cities rises to 17, the maximum 8-h O3 concentration reduction rate in Shanghai will increase to 7.8%. It is also recommended that the VOCs:NOx reduction ratio should be strictly controlled at more than 3:1, or else the O3 concentration in some areas will increase.

Highly Resolved Dynamic Emissions of Air Pollutants and Greenhouse Gas CO2 during COVID-19 Pandemic in East China.

The unintentional emission reductions caused by the COVID-19 pandemic provides an opportunity to investigate the impact of energy, industry, and transportation activities on air pollutants and CO2 emissions and their synergy. Here, we constructed an approach to estimate city-level high resolution dynamic emissions of both anthropogenic air pollutants and CO2 by introducing dynamic temporal allocation coefficients based on real-time multisource activity data. We first apply this approach to estimate the spatiotemporal evolution of sectoral emissions in eastern China, focusing on the period around the COVID-19 lockdown. Comparisons with observational data show that our approach can well capture the spatiotemporal changes of both short-lived precursors (NOx and NMVOCs) and CO2 emissions. Our results show that air pollutants (SO2, NOx, and NMVOCs) were reduced by up to 31%-53% during the lockdown period accompanied by simultaneous changes of 40% CO2 emissions. The declines in power and heavy industry sectors dominated regional SO2 and CO2 reductions. NOx reductions were mainly attributed to mobile sources, while NMVOCs emission reductions were mainly from light industry sectors. Our findings suggest that differentiated emission control strategies should be implemented for different source categories to achieve coordinated reduction goals.

[Ozone Sensitivity Analysis and Emission Controls in Dezhou in Summer].

In recent years, there have been frequent ozone pollution episodes in Dezhou, China. In the summer of 2018 (from June to August), Dezhou experienced serious ozone pollution episodes. The daily 8-hour maximum ozone concentrations exceeded the national standard for 60 days with the standard exceeding ratio of 65%. The average of daily 8-hour maximum ozone concentration was 176 µg ·m-3 over these three months, and the highest value reached was 262 µg ·m-3. In this study, the WRF-CAMx model coupled with the higher-order decoupled direct method (HDDM) was used to analyze the ozone sensitivity and emission control plans in Dezhou during this period. The results showed that ozone formation was in the strong VOC-limited regime in the urban area of Dezhou, while it was in the NOx and VOCs transition regime in suburban areas. VOCs sensitivity values (dO3_V50) were positive every day in summer, which was higher in June (18.7 µg ·m-3 in urban area, 19.7 µg ·m-3 in suburban area) and August (15.3 µg ·m-3 in urban area, 16.4 µg ·m-3 in suburban area) than in July (13.0 µg ·m-3 in urban area, 11.8 µg ·m-3 in suburban area). NOx sensitivity values (dO3_N50) were positive or negative in the urban area, and most days were positive in the suburban area, which were close to the VOCs sensitivity values. For urban areas, VOC reduction should be the priority for emission reduction plans, whereas for suburban areas, NOx：VOCs=1：1 is recommended because the reductions in NOx and VOCs emissions had the same effect on ozone pollution control.

Driving Forces of Changes in Air Quality during the COVID-19 Lockdown Period in the Yangtze River Delta Region, China.

During the COVID-19 lockdown period (from January 23 to February 29, 2020), ambient PM2.5 concentrations in the Yangtze River Delta (YRD) region were observed to be much lower, while the maximum daily 8 h average (MDA8) O3 concentrations became much higher compared to those before the lockdown (from January 1 to 22, 2020). Here, we show that emission reduction is the major driving force for the PM2.5 change, contributing to a PM2.5 decrease by 37% to 55% in the four YRD major cities (i.e., Shanghai, Hangzhou, Nanjing, and Hefei), but the MDA8 O3 increase is driven by both emission reduction (29%-52%) and variation in meteorological conditions (17%- 49%). Among all pollutants, reduction in emissions mainly of primary PM contributes to a PM2.5 decrease by 28% to 46%, and NOx emission reduction contributes 7% to 10%. Although NOx emission reduction dominates the MDA8 O3 increase (38%-59%), volatile organic compounds (VOCs) emission reduction lead to a 5% to 9% MDA8 O3 decrease. Increased O3 promotes secondary aerosol formation and partially offsets the decrease of PM2.5 caused by the primary PM emission reductions. The results demonstrate that more coordinated air pollution control strategies are needed in YRD.

[Secondary Aerosol Formation in Urban Shanghai: Insights into the Roles of Photochemical Oxidation and Aqueous-Phase Reaction].

Secondary species are one of the most important components of PM1 particles. To investigate the contributions as well as the factors that affect the formation of the secondary aerosols, a high-resolution time-of-flight aerosol mass spectrometer (HR-TOF-AMS, AMS) was employed to characterize sub-micron particles (PM1) during spring and summer in urban Shanghai. Organics were dominant in PM1 particles and comprised around 55% of the total PM1 mass concentration, followed by sulfate (24%) and nitrate (10%). Positive matrix factorization was further applied to explore the sources of the organics. It was found that primary and secondary organic aerosols accounted for around 34% and 66% of the total organics, respectively. Three episodes were observed during the measurements, where secondary species increased substantially. Increases of secondary species were represented by increases of sulfate and LV-OOA1 in spring, especially during the noontime, thus indicating that their formation is promoted by photochemical oxidation; yet in summer, photochemical and aqueous chemistry together accelerate the formation of secondary species, as indicated by the good correlations between nitrate and aerosol liquid water as well as between SOA and Ox. Overall, we found that contributions from secondary organic and inorganic aerosols to total PM1 particles were 35.5% and 43%, respectively. This study highlights that the influence of photochemical and aqueous chemistry is significant in the promotion of secondary species formation in Shanghai.

[Health Benefit Analyses of the Clean Air Action Plan Implementation in Shanghai].

To understand the public health benefits of the Clean Air Action Plan implemented in Shanghai from 2013-2017, the changes of the PM2.5 exposure levels and related health and economic benefits were quantitatively evaluated by using air quality numerical modeling, health risk assessment, and environmental valuation methods. The results show that the proportion of the population exposed to a mean annual PM2.5 concentration lower than or equal to 35 µg·m-3 has increased from 1.62% in the base year to 34.06% in the control year. The death risk attributable to ambient PM2.5 exposure decreased from 15.2% in the base year to 11.9% in the control year. The total health benefits are approximately 11.841 billion RMB(95% CI:5.024-17.819 billion RMB), accounting for 0.55%(95% CI:0.23%-0.82%)of Shanghai's GDP in 2013. The implementation of the action plan has a positive effect on the protection of the health of the population. Health benefits in areas with dense populations and high PM2.5 declines are more pronounced within the outer ring line of Shanghai City.

An Integrated Source Apportionment Methodology and Its Application over the Yangtze River Delta Region, China.

An integrated source apportionment methodology is developed by amalgamating the receptor-oriented model (ROM) and source-oriented numerical simulations (SOM) together to eliminate the weaknesses of individual SA methods. This approach attempts to apportion and dissect the PM2.5 sources in the Yangtze River Delta region during winter. First, three ROM models (CMB, PMF, ME2) are applied and compared for the preliminary SA results, with information from PM2.5 sampling and lab analysis during the winter seasons. The detailed source category contribution of SOM to PM2.5 is further simulated using the WRF-CAMx model. The two pieces of information from both ROM and SOM are then stitched together to give a comprehensive information on the PM2.5 sources over the region. With the integrated approach, the detailed contributing sources of the ambient PM2.5 at different receptors including rural and urban, coastal and in-land, northern and southern receptors are analyzed. The results are compared with previous data and shows good agreement. This integrative approach is more comprehensive and is able to produce a more profound and detailed understanding between the sources and receptors, compared with single models.

[Emissions, Chemical Composition, and Spatial and Temporal Allocation of the BVOCs in the Yangtze River Delta Region in 2014].

Based on the land surface vegetation data interpreted via remote sensing and the meteorological conditions predicted via the WRF model, the MEGAN model was applied to calculate the regional BVOC emissions in the Yangtze River Delta (YRD) in 2014. The chemical components and the temporal and spatial allocations were further analyzed. Results show that the annual BVOC emissions in the YRD were 1886 kt, in which isoprene emissions were 704.2 kt (accounting for 37.3%), monoterpenes 303 kt (16.1%), and other VOCs 878.8 kt (46.6%). Seasonal variation of the BVOC emissions was very significant. The BVOC emissions had a strong seasonal pattern, with maximum emissions in summer, accounting for 60.9% (1088 kt) of the total, whereas the minimum emissions occurred in winter, accounting for 3.2% (57 kt). Spatially, the southern YRD produced more BVOC emissions than the northern part did. In Zhejiang, Anhui, Jiangsu, and Shanghai, the BVOC emissions were 842 kt (44.6%), 760 kt (40.3%), 272 kt (14.4%), and 12 kt (0.7%), respectively. This is mainly related to the distribution of vegetation types.

[Ozone source apportionment at urban area during a typical photochemical pollution episode in the summer of 2013 in the Yangtze River Delta].

With the fast development of urbanization, industrialization and mobilization, the air pollutant emissions with photochemical reactivity become more obvious, causing a severe photochemical pollution with the characteristics of high ozone concentration. However, the ozone source identification is very complicated due to the high non linearity between ozone and its precursors. Thus, ways to reduce ozone is still not clear. A high ozone pollution episode occurred during July, 2013, which lasted for a long period, with large influence area and high intensity. In this paper, we selected this episode to do a case study with the application of ozone source apportionment technology(OSAT) coupled within the CAMx air quality model. In this study, 4 source regions(including Shanghai, north Zhejiang, South Jiangsu and long range transport), 7 source categories (including power plants, industrial process, industrial boilers and kilns, residential, mobile source, volatile source and biogenic emissions) are analyzed to study their contributions to surface O3 in Shanghai, Suzhou and Zhejiang. Results indicate that long range transport contribution to the surface ozone in the YRD is around 20 x 10(-9) - 40 x 10(-9) (volume fraction). The O3 concentrations can increased to 40 x 10(-9) - 100 x 10(-9) (volume fraction) due to precursors emissions in Shanghai, Jiangsu and Zhejiang. As for the regional contribution to 8 hour ozone, long range transport constitutes 42.79% +/- 10.17%, 48.57% +/- 9.97% and 60.13% +/- 7.11% of the surface ozone in Shanghai, Suzhou and Hangzhou, respectively. Regarding the high O3 in Shanghai, local contribution is 28.94% +/- 8.49%, north Zhejiang constitutes 19.83% +/- 10.55%. As for surface O3 in Suzhou, the contribution from south Jiangsu is 26.41% +/- 6.80%. Regarding the surface O3 in Hangzhou, the major regional contributor is north Zhejiang (29.56% +/- 8.33%). Contributions from the long range transport to the daily maximum O3 concentrations are slightly lower than those to the 8-hourly O3, with the contribution of 35.35%-58.04%, while local contributions increase. As for the contributions from source sectors, it is found that the major source contributors include industrial boilers and kilns (18.4%-21.11%), industrial process (19.85%-28.46%), mobile source (21.30%-23.51%), biogenic (13.01%-17.07%) and power plants (7.08%-9.75%). Thus, industrial combustion, industrial processes, and mobile source are major anthropogenic sources of high ozone pollution in summer in the YRD region.

[Source Contribution Analysis of the Fine Particles in Shanghai During a Heavy Haze Episode in December, 2013 Based on the Particulate Matter Source Apportionment Technology].

The haze pollution caused by high PM2.5 concentrations has become one of the major environmental issues restricting urban and regional sustainable development in China in recent years. Therefore, the diagnosis of the pollution sources of PM2.5 and its major components in a scientific and efficient way is of great significance both scientifically and theoretically. A rare heavy haze pollution event occurred in Shanghai and the surrounding Yangtze River Delta in early December, 2013, that the hourly PM2.5 concentration reached 640 µg x m(-3). In this study, we analyzed the three typical episodes that occurred in Shanghai during this period. The particulate matter source apportionment technology (PSAT) was applied to study the source contributions to PM2.5 and its major components. Results showed that NO3-(2.5) were mostly contributed by industrial boilers and kilns, transportation and power plants. Comparatively, most of the SO4(2-) 2.5 came from industry and transport sectors. During the three episodes including haze, foggy haze and transport, local emissions contributed 35.3%, 44.8%, 22.7%, while super-regional transport accounted for 42.0%, 41.1% and 59.8% to PM2.5, respectively. In the YRD modeling domain, fugitive dust, industrial processing, volatile source, industrial boilers and kilns and transport were the major contributors to high concentrations of PM2.5, with the average contributions of 25.1%, 14.9%, 15.8%, 13.7% and 15.9%, respectively. Results showed that the very heavy haze pollution is usually not caused by a single city, the regional joint pollution control is of great importance to relieve the pollution level.