Severe ozone (O
) episodes occur frequently in Shanghai during late-summers. We define geopotential height averaged over the key area region (122.5°E-135°E, 27.5°N -35°N) at 500 hPa as a WPSH_SHO
...index which has high positive correlation with surface O
concentration in Shanghai. In addition, the index has a significant long-term increasing trend during the recent 60 years. Analysis shows the meteorological conditions under the strong WPSH_SHO
climate background (compared to the weak background) have several important anomalies: (1) A strong WPSH center occurs over the key area region. (2) The cloud cover is less, resulting in high solar radiation and low humidity, enhancing the photochemical reactions of O
. (3) The near-surface southwesterly winds are more frequent, enhancing the transport of upwind pollutants and O
precursors from polluted regions to Shanghai and producing higher O
chemical productions. This study suggests that the global climate change could lead to a stronger WPSH in the key region, enhancing ozone pollution in Shanghai. A global chemical/transport model (MOZART-4) is applied to show that the O
concentrations can be 30 ppbv higher under a strong WPSH_SHO
condition than a weak condition, indicating the important effect of the global climate change on local air pollution in Shanghai.
Severe haze in northern China An, Zhisheng; Huang, Ru-Jin; Zhang, Renyi ...
Proceedings of the National Academy of Sciences - PNAS,
04/2019, Letnik:
116, Številka:
18
Journal Article
Recenzirano
Odprti dostop
Regional severe haze represents an enormous environmental problem in China, influencing air quality, human health, ecosystem, weather, and climate. These extremes are characterized by exceedingly ...high concentrations of fine particulate matter (smaller than 2.5 μm, or PM2.5) and occur with extensive temporal (on a daily, weekly, to monthly timescale) and spatial (over a million square kilometers) coverage. Although significant advances have been made in field measurements, model simulations, and laboratory experiments for fine PM over recent years, the causes for severe haze formation have not yet to be systematically/comprehensively evaluated. This review provides a synthetic synopsis of recent advances in understanding the fundamental mechanisms of severe haze formation in northern China, focusing on emission sources, chemical formation and transformation, and meteorological and climatic conditions. In particular, we highlight the synergetic effects from the interactions between anthropogenic emissions and atmospheric processes. Current challenges and future research directions to improve the understanding of severe haze pollution as well as plausible regulatory implications on a scientific basis are also discussed.
The causes of haze formation in Beijing, China were analyzed based on a comprehensive measurement, including PBL (planetary boundary layer), aerosol composition and concentrations, and several ...important meteorological parameters such as visibility, RH (relative humidity), and wind speed/direction. The measurement was conducted in an urban location from Nov. 16, 2012 to Jan. 15, 2013. During the period, the visibility varied from >20km to less than a kilometer, with a minimum visibility of 667m, causing 16 haze occurrences. During the haze occurrences, the wind speeds were less than 1m/s, and the concentrations of PM2.5 (particle matter with radius less than 2.5μm) were often exceeded 200μg/m3. The correlation between PM2.5 concentration and visibility under different RH values shows that visibility was exponentially decreased with the increase of PM2.5 concentrations when RH was less than 80%. However, when RH was higher than 80%, the relationship was no longer to follow the exponentially decreasing trend, and the visibility maintained in very low values, even with low PM2.5 concentrations. Under this condition, the hygroscopic growth of particles played important roles, and a large amount of water vapor acted as particle matter (PM) for the reduction of visibility. The variations of meteorological parameters (RH, PBL heights, and WS (wind speed)), chemical species in gas-phase (CO, O3, SO2, and NOx), and gas-phase to particle-phase conversions under different visibility ranges were analyzed. The results show that from high visibility (>20km) to low visibility (<2km), the averaged PBL decreased from 1.24km to 0.53km; wind speeds reduced from 1m/s to 0.5m/s; and CO increased from 0.5ppmv to 4.0ppmv, suggesting that weaker transport/diffusion caused the haze occurrences. This study also found that the formation of SPM (secondary particle matter) was accelerated in the haze events. The conversions between SO2 and SO4 as well as NOx to NO3− increased, especially under high humidity conditions. When the averaged RH was 70%, the conversions between SO2 and SO4 accounted for about 20% concentration of PM2.5, indicating that formation of secondary particle matter had important contribution for the haze occurrences in Beijing.
•The cases of haze formation in Beijing, China were analyzed.•The effects of RH on PM2.5 concentration and visibility were studied.•Gas-phase to particle-phase conversion under different visibility was analyzed.•With high RH, the conversion SO2 to SO4= accounted for 20%.
A comprehensive measurement was carried out to analyze the heavy haze events during 2012–2013 winter in Beijing. The measured variables include some important meteorological parameters, such wind ...directions, wind speeds, relative humidity (RH), planetary boundary layer (PBL), solar radiation, and visibility. The aerosol composition and concentrations (including particular matters (PM2.5), nitrate (NO3), sulfate (SO4), ammonium (NH4)) as well as their gas-phase precursors (including nitrogen oxides (NOx) and sulfur dioxide (SO2)) were analyzed during the period between Nov. 16, 2012 and Jan. 15, 2013. The results show that the hourly mean concentrations of PM2.5 often exceeded 200 μg/m3, with a maximum concentration of 600 μg/m3 on Jan. 13, 2013. The relative humidity was increased during the haze events, indicating that both aerosol concentrations and RH had important effect on the reduction of visibility, causing the occurrence of the haze events. Because the wind speeds were generally low (less than 1 m/s) during the haze event, the vertical dispersion and the PBL heights were very important factors for causing the strong variability of aerosol concentrations. This study also finds that under the lower visibility condition, the conversion from the gas-phase of NOx and SO2 to the particle phase of NO3 and SO4 were higher than the values under the higher visibility condition. Because the lower visibility condition was corresponding to the lower photochemical activity than the higher visibility condition, the higher conversion from gas phase to particle phase in the lower visibility condition indicated that there was important heterogeneous formation of NO3 and SO4 during the heavy haze events.
•Both aerosol concentrations and RH had strong effect for the occurrence of the haze events.•The lower PBL height in haze events leads to an increase in the surface aerosol concentrations.•During the heavy haze events, higher heterogeneous conversions from gas to particle phases of NOx and SO2 was observed.
The fine particles (PM2.5) in China have decreased significantly in
recent years as a result of the implementation of Chinese Clean Air Action Plan
since 2013, while the O3 pollution is getting ...worse, especially in
megacities such as Beijing and Shanghai. Better understanding of the elevated
O3 pollution in Chinese megacities and its response to emission change
is important for developing an effective emission control strategy in
the future. In this study, we analyze the significant increasing trend of daily
maximum O3 concentration from 2006 to 2015 in the megacity Shanghai
with the variability of 0.8–1.3 ppbv yr−1. It could likely be attributed to
the notable reduction in NOx concentrations with the decreasing rate of
1.86–2.15 ppbv yr−1 accompanied by the small change in VOCs during
the same period by excluding the weak trends of meteorological impacts on
local dispersion (wind speed), regional transport (wind direction), and
O3 photolysis (solar radiation). It is further illustrated by using a
state-of-the-art regional chemical and dynamical model (WRF-Chem) to explore the
O3 variation response to the reduction in NOx emissions in
Shanghai. The control experiment conducted for September of 2009 shows
excellent performance for O3 and NOx simulations, including both
the spatial distribution pattern and the day-by-day variation through
comparison with six in situ measurements from the MIRAGE-Shanghai field campaign.
Sensitivity experiments with 30 % reduction in NOx emissions from 2009
to 2015 in Shanghai estimated by Shanghai Environmental Monitoring Center
shows that the calculated O3 concentrations exhibit obvious enhancement
by 4–7 ppbv in urban zones with increasing variability of 0.96–1.06 ppbv yr−1, which is consistent with the observed O3 trend as a
result of the strong VOC-limited condition for O3 production. The large
reduction in NOx combined with less change in VOCs in the past 10
years promotes the O3 production in Shanghai to move towards
an NOx-limited regime. Further analysis of the WRF-Chem experiments and
O3 isopleth diagram suggests that the O3 production downtown
is still under a VOC-limited regime after 2015 despite the remarkable
NOx reduction, while it moves to the transition regime between
NOx-limited and VOC-limited in sub-urban zones. Supposing the
insignificant VOC variation persists, the O3 concentration downtown
would keep increasing until 2020 with the further 20 % reduction in
NOx emission after 2015 estimated by Shanghai Clean Air Action Plan.
The O3 production in Shanghai will switch from a VOC-limited to
an NOx-limited regime after 2020 except for downtown area, which is likely
close to the transition regime. As a result the O3 concentration will
decrease by 2–3 ppbv in sub-urban zones and by more than 4 ppbv in rural areas as a response to a 20 % reduction in NOx emission after 2020, whereas it is not
sensitive to both NOx and VOC changes downtown. This result reveals
that the control strategy of O3 pollution is a very complex process
and needs to be carefully studied.
Volatile organic compounds (VOCs) were measured from 2007 to 2010 at the center of Shanghai, China. Because VOCs are important precursors for ozone photochemical formation, detailed information of ...VOC sources needs to be investigated. The results show that the measured VOC concentrations in Shanghai are dominated by alkanes (43%) and aromatics (30%), following by halo-hydrocarbons (14%) and alkenes (6%). Based on the measured VOC concentrations, a receptor model (PMF; positive matrix factorization) coupled with the information related to VOC sources (the distribution of major industrial complex, meteorological conditions, etc.) is applied to identify the major VOC sources in Shanghai. The result shows that seven major VOC sources are identified by the PMF method, including (1) vehicle related source which contributes to 25% of the measured VOC concentrations, (2) solvent based industrial source to 17%, (3) fuel evaporation to 15%, (4) paint solvent usage to 15%, (5) steel related industrial production to 12%, (6) biomass/biofuel burning to 9%, and (7) coal burning to 7%. Furthermore, ozone formation potential related to VOC sources is calculated by the MIR (maximum incremental reactivity) technique. The most significant VOC source for ozone formation potential is solvent based industrial sources (27%), paint solvent usage (24%), vehicle related emissions (17%), steel related industrial productions (14%), fuel evaporations (9%), coal burning (6%), and biomass/biofuel burning (3%). The weekend effect on the VOC concentrations shows that VOC concentrations are generally higher in the weekdays than in the weekends at the sampling site, suggesting that traffic conditions and human activities have important impacts on the VOC emissions in Shanghai.
In recent years, China and other emerging countries have been experiencing severe air pollution problems with high concentrations of atmospheric aerosol particles. Satellite measurements indicate ...that the aerosol loading of the atmosphere in highly populated regions of China is about 10 times higher than, for example, in Europe and in the Eastern United States. The exposure to extremely high aerosol concentrations might lead to important human health effects, including respiratory and cardiovascular diseases as well as lung cancers. Here, we analyze 52-year historical surface measurements of haze data in the Chinese city of Guangzhou, and show that the dramatic increase in the occurrence of air pollution events between 1954 and 2006 has been followed by a large enhancement in the incidence of lung cancer.
With its dense population, rapid economic growth and dramatic rate of urbanization, China is experiencing extreme air pollution problems. This is particularly the case in Central-Eastern China （CEC）, ...where the two major cities of Beijing and Tianjin are located, in the Yangtze-River Delta （YRD） with the city of Shanghai, and in the Pearl-River Delta （PRD） with the mega-city of Gnangzhou. Space observations show that the atmospheric aerosol load in these three regions is considerably higher than, for example, in the urbanized regions of Europe and North America. The high aerosol concentrations in these regions have raised many environmental problems, such as impact on human health, visibility, and climate changes. In this paper, several crucial issues regarding aerosol pollution in these highly populated regions （CEC, YRD, and PRD） are discussed, including （1） when the aerosol load starts to rapidly increase in these regions; （2） how the high aerosol concentrations affects the environment; and （3） what the potential consequences are under possible low aerosol load in these regions. Discussion on these crucial issues might lead to some insight for better understanding of the characterizations of aerosol pollution due to the rapid economical development in China.
Rapid industrialization and urbanization have caused frequent occurrence of haze in China during wintertime in recent years. The sulfate aerosol is one of the most important components of fine ...particles (PM2. 5) in the atmosphere, contributing significantly to the haze formation. However, the heterogeneous formation mechanism of sulfate remains poorly characterized. The relationships of the observed sulfate with PM2. 5, iron, and relative humidity in Xi'an, China have been employed to evaluate the mechanism and to develop a parameterization of the sulfate heterogeneous formation involving aerosol water for incorporation into atmospheric chemical transport models. Model simulations with the proposed parameterization can successfully reproduce the observed sulfate rapid growth and diurnal variations in Xi'an and Beijing, China. Reasonable representation of sulfate heterogeneous formation in chemical transport models considerably improves the PM2. 5 simulations, providing the underlying basis for better understanding the haze formation and supporting the design and implementation of emission control strategies.
A field experiment was conducted in Tianjin, China from September 9-30, 2010, focused on the evolution of Planetary Boundary Layer （PBL） and its impact on surface air pollutants. The experiment used ...three remote sensing instruments, wind profile radar （WPR）, microwave radiometer （MWR） and micro-pulse lidar （MPL）, to detect the vertical profiles of winds, temperature, and aerosol backscattering coefficient and to measure the vertical profiles of surface pollutants （aerosol, CO, SO2, NOx）, and also collected sonic anemometers data from a 255-m meteorological tower. Based on these measurements, the evolution of the PBL was estimated. The averaged PBL height was about 1000-1300 m during noon/afternoon-time, and 200-300 m during night-time. The PBL height and the aerosol concentrations were anti-correlated during clear and haze conditions. The averaged maximum PBL heights were 1.08 and 1.70 km while the averaged aerosol concentrations were 52 and 17 μg/m＆3 under haze and clear sky conditions, respectively, The influence of aerosols and clouds on solar radiation was observed based on sonic anemometers data collected from the 255-m meteorological tower. The heat flux was found significantly decreased by haze （heavy pollution） or cloud, which tended to depress the development of PBL, while the repressed structure of PBL further weakened the diffusion of pollutants, leading to heavy pollution. This possible positive feedback cycle （more aerosols→lower PBL height → more aerosols） would induce an acceleration process for heavy ground pollution in megacities.
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