The nationwide extent of surface ozone pollution in China and its comparison to the global ozone distribution have not been recognized because of the scarcity of Chinese monitoring sites before 2012. Here we address this issue by using the latest 5 year (2013–2017) surface ozone measurements from the Chinese monitoring network, combined with the recent Tropospheric Ozone Assessment Report (TOAR) database for other industrialized regions such as Japan, South Korea, Europe, and the United States (JKEU). We use various human health and vegetation exposure metrics. We find that although the median ozone values are comparable between Chinese and JKEU cities, the magnitude and frequency of high-ozone events are much larger in China. The national warm-season (April–September) fourth highest daily maximum 8 h average (4MDA8) ozone level (86.0 ppb) and the number of days with MDA8 values of >70 ppb (NDGT70, 29.7 days) in China are 6.3–30% (range of regional mean differences) and 93–575% higher, respectively, than ...

Severe Surface Ozone Pollution in China: A Global Perspective

Amplified ozone pollution in cities during the COVID-19 lockdown.

Fine particulate matter (PM2.5) decreased by 30–40% across China during 2013–2017 in response to the governmental Clean Air Action. However, surface ozone pollution worsened over the same period. Model simulations have suggested that the increase in ozone could be driven by the decrease in PM2.5, because PM2.5 scavenges hydroperoxy (HO2) and NOx radicals that would otherwise produce ozone. Here we show observational evidence for this effect with 2013–2018 summer data of hourly ozone and PM2.5 concentrations from 106 sites in the North China Plain. The observations show suppression of ozone pollution at high PM2.5 concentrations, consistent with a model simulation in which PM2.5 scavenging of HO2 and NOx depresses ozone concentrations by 25 ppb relative to PM2.5-free conditions. PM2.5 chemistry makes ozone pollution less sensitive to NOx emission controls, emphasizing the need for controlling emissions of volatile organic compounds (VOCs), which so far have not decreased in China. The new 2018–2020 Clean Air Action plan calls for a 10% decrease in VOC emissions that should begin to reverse the long-term ozone increase even as PM2.5 continues to decrease. Aggressive reduction of NOx and aromatic VOC emissions should be particularly effective for decreasing both PM2.5 and ozone. Observations confirm that cleaning up fine particulate matter in the North China Plain has exacerbated ozone pollution, suggesting that both NOx and VOC emissions need to be reduced to improve air quality.

A two-pollutant strategy for improving ozone and particulate air quality in China

China’s nationwide ozone monitoring network initiated in 2013 has observed severe surface ozone pollution. This network, combined with the recent Tropospheric Ozone Assessment Report (TOAR) data set, offers a more comprehensive view on global surface ozone distribution and trends. Here, we report quantitative estimates of the warm-season (April–September) surface ozone trends and resulting health impacts at Chinese cities in 2013–2019. Both the parametric and nonparametric linear trends for 12 ozone metrics relevant to human health and vegetation exposure are derived. We find that all ozone metrics averaged from Chinese urban sites have increased significantly since 2013. The warm-season daily maximum 8-h average (MDA8) ozone levels increased by 2.4 ppb (5.0%) year–¹, with over 90% of the sites showing positive trends and 30% with trends larger than 3.0 ppb year–¹. These rates are among the fastest trends, even faster in some Chinese cities, compared with the urban ozone trends in any other region worldwide reported in TOAR. Ozone metrics reflecting the cumulative exposure effect on human health and vegetation such as SOMO35 and AOT40 have increased at even faster rates (>10% year–¹). We estimate that the total premature respiratory mortalities attributable to ambient MDA8 ozone exposure in 69 Chinese cities are 64,370 in 2019, which has increased by 60% compared to 2013 levels and requires urgent attention.

Rapid Increases in Warm-Season Surface Ozone and Resulting Health Impact in China since 2013

. Severe surface ozone pollution over major Chinese cities has become an
emerging air quality concern, raising a new challenge for emission control
measures in China. In this study, we explore the source contributions to
surface daily maximum 8 h average (MDA8) ozone over China in 2016 and 2017,
the 2 years with the highest surface ozone averaged over Chinese cities in
record. We estimate the contributions of anthropogenic, background, and
individual natural sources to surface ozone over China using the GEOS-Chem
chemical transport model at 0.25 ∘ × 0.3125 ∘ 
horizontal resolution with the most up-to-date Chinese anthropogenic
emission inventory. Model results are evaluated with concurrent surface
ozone measurements at 169 cities over China and show generally good agreement.
We find that background ozone (defined as ozone that would be present in
the absence of all Chinese anthropogenic emissions) accounts for 90 %
(49.4 ppbv) of the national March–April mean surface MDA8 ozone over China
and 80 % (44.5 ppbv) for May–August. It includes large contributions from
natural sources (80 % in March–April and 72 % in May–August). Among
them, biogenic volatile organic compound (BVOC) emissions enhance MDA8
ozone by more than 15 ppbv in eastern China during July–August, while
lightning NOx emissions and ozone transport from the stratosphere both
lead to ozone enhancements of over 20 ppbv in western China during
March–April. Over major Chinese city clusters, domestic anthropogenic
sources account for about 30 % of the May–August mean surface MDA8 ozone
and reach 39–73 ppbv (38 %–69 %) for days with simulated MDA8 ozone
 > 100  ppbv in the North China Plain, Fenwei Plain, Yangtze
River Delta, and Pearl River Delta city clusters. These high ozone episodes
are usually associated with high temperatures, which induce large BVOC
emissions and enhance ozone chemical production. Our results indicate that
there would be no days with MDA8 ozone > 80  ppbv in these major
Chinese cities in the absence of domestic anthropogenic emissions. We find
that the 2017 ozone increases relative to 2016 are largely due to higher
background ozone driven by hotter and drier weather conditions, while
changes in domestic anthropogenic emissions alone would have led to ozone
decreases in 2017. Meteorological conditions in 2017 favor natural source
contributions (particularly soil NOx and BVOC ozone enhancements) and
ozone chemical production, increase the thermal decomposition of peroxyacetyl
nitrate (PAN), and further decrease ozone dry deposition velocity. More
stringent emission control measures are thus required to offset the adverse
effects of unfavorable meteorology, such as high temperature, on surface ozone
air quality.

/pdf/exploring-2016-2017-surface-ozone-pollution-over-china-4ofd2utgwr.pdf

Exploring 2016–2017 surface ozone pollution over China: source contributions and meteorological influences

Ground-level ozone pollution and its health impacts in China

. With the fast development of seaborne trade and relatively more efforts on
reducing emissions from other sources in China, shipping emissions contribute
more and more significantly to air pollution. In this study, based on a
shipping emission inventory with high spatial and temporal resolution within
200 nautical miles (Nm) to the Chinese coastline, the Community Multiscale
Air Quality (CMAQ) model was applied to quantify the impacts of the shipping
sector on the annual and seasonal concentrations of PM 2.5 for the base
year 2015 in China. Emissions within 12 Nm accounted for
51.2 %–56.5 % of the total shipping emissions, and the distinct
seasonal variations in spatial distribution were observed. The modeling
results showed that shipping emissions increased the annual averaged
PM 2.5 concentrations in eastern China up to
5.2  µ g m −3 , and the impacts in YRD
(Yangtze River Delta) and PRD (Pearl River Delta) were much greater than
those in BTH (Beijing–Tianjin–Hebei). Shipping emissions influenced the air
quality in not only coastal areas but also the inland areas hundreds of
kilometers (up to 960 km) away from the sea. The impacts on the PM 2.5 
showed obvious seasonal variations, and patterns in the north and south of
the Yangtze River were also quite different. In addition, since the onshore
wind can carry ship pollutants to inland areas, the daily contributions of
shipping emissions in onshore flow days were about 1.8–2.7 times higher than
those in the rest of the days. A source-oriented CMAQ was used to estimate the
contributions of shipping emissions from maritime areas within 0–12, 12–50,
50–100 and 100–200 Nm to PM 2.5 concentrations. The results
indicated that shipping emissions within 12 Nm were the dominant
contributor,
with contributions 30 %–90 % of the total impacts induced by
emissions within 200 Nm, while a relatively high contribution
(40 %–60 %) of shipping emissions within 20–100 Nm was
observed in the north of the YRD region and south of Lianyungang, due to the
major water traffic lanes far from land. The results presented in this work
implied that shipping emissions had significant influence on air quality in
China, and to reduce its pollution, the current Domestic Emission Control
Area (DECA) should be expanded to at least 100 Nm from the coastline.

/pdf/impacts-of-shipping-emissions-on-pm-2-5-pollution-in-china-46ko614z6h.pdf

Impacts of shipping emissions on PM 2.5 pollution in China

Global shipping activity emits 938 million tonnes of carbon dioxide annually, surpassing the eighth highest emitting country. Although the impacts from the shipping industry have been investigated over the past three decades, allocating responsibilities remains a difficult issue. Numerous parties should share the responsibility and quantitative analysis is therefore required when considering the interaction between the global economy, shipping and ecological connectivity. Here, beginning with our shipping emission inventory model based on satellite-observed vessel activities, we evaluated trade-embodied shipping emissions and their impacts on human health. Combined with international trade databases, we traced shipping impacts back to responsible bilateral trade and proposed an integrated trade–shipping–air quality–health impact nexus. Quantitative analysis shows that the US–China bilateral trade is responsible for 2.5% of the global shipping carbon dioxide emissions and 4.8% of ship-related global premature deaths caused by air pollution. Our research provides the methodology to allocate intercontinental responsibilities to trade pairs and ships. International shipping is a major emitter of greenhouse gases, but quantifying responsibilities has been difficult. This study uses satellite-observed data on vessels to determine the emissions from and subsequent health impacts of US–China bilateral trade of goods.

Emissions and health impacts from global shipping embodied in US–China bilateral trade

Shipping emission forecasts and cost-benefit analysis of China ports and key regions’ control

A new study taking a first look at China’s domestic coastal shipping sector and providing recommendations for actionable long-term decarbonization pathways shows that with mandatory energy efficiency standards and low-carbon fuel regulations, CO 2 emissions from China’s domestic coastal shipping could peak by 2040 and fall significantly by 2060. Two pathways are proposed for achieving the carbon peaking and neutrality goal in China’s domestic coastal shipping sector: The low-carbon fuel regulations should be implemented no later than 2030 to provide sufficient time for development of related industry and technologies. If delayed until 2046 after expiration of mandatory energy efficiency standards, it would be dauntingly difficult to meet the decarbonization goal of the sector.

Zhi-Hang Meng

Papers

Ground-level ozone pollution and its health impacts in China

Impacts of shipping emissions on PM 2.5 pollution in China

Emissions and health impacts from global shipping embodied in US–China bilateral trade

Shipping emission forecasts and cost-benefit analysis of China ports and key regions’ control

Decarbonizing China’s coastal shipping: The role of fuel efficiency and low-carbon fuels