Severe Haze Pollution Research Articles

Investigating vertical distribution patterns of lower tropospheric PM2.5 using unmanned aerial vehicle measurements

A lightweight unmanned aerial vehicle (UAV) was outfitted with miniaturized sensors to investigate the vertical distribution patterns and sources of fine aerosol particles (PM2.5) within the 1 000 m lower troposphere. A total of 16 UAV flights were conducted in the Yangtze River Delta (YRD) region, China, from the summer to winter in 2014. The associated ground-level measurements from two environmental monitoring stations were also used for background analysis. The results show that ground-level PM2.5 concentrations demonstrated a decreasing trend from Feb. to Jul. and an increasing trend from Aug. to Jan. (the following year). Higher PM2.5 concentrations during the day were mainly observed in the morning (Local Time, LT 05-09) in the spring and summer. However, higher PM2.5 concentrations occurred mainly in the late afternoon and evening (LT 16-20) in the autumn and winter, excluding severe haze pollution days when higher PM2.5 concentrations were also observed during the morning periods. Lower tropospheric PM2.5 concentrations exhibited similar diurnal vertical distribution patterns from the summer to winter. The PM2.5 concentrations decreased with height in the morning, with significantly large vertical gradients from the summer to winter. By contrast, the aerosol particles were well mixed with PM2.5 concentrations of lower than 35 μg⋅m−3 in the early afternoon (LT 12-16) due to sufficient expansions of the planetary boundary layer. The mean vertical PM2.5 concentrations within the 1 000 m lower troposphere in the morning were much larger in the winter (∼87.5 μg⋅m−3) than in the summer and autumn (∼20 μg⋅m−3). However, subtle differences of ∼11 μg⋅m−3 in the mean vertical PM2.5 concentrations were observed in the early afternoon from the summer to winter. The vertical distribution patterns of black carbon and its relationships with PM2.5 indicated that the lower tropospheric aerosol particles might be mainly derived from fossil-fuel combustion sources. In addition, a 48-h backward trajectory analysis of air parcels showed that the lower tropospheric aerosol particles were mainly from emissions of local sources in the YRD region in the summer and autumn. By sharp contrast, the aerosol particles of this region in the winter were mainly of long-range transport sources from the north and northwest China due to the impact of Asian winter monsoon.

Role of atmospheric circulations in haze pollution in December 2016

Abstract. In the east of China, recent haze pollution has been severe and damaging. In addition to anthropogenic emissions, atmospheric circulations and local meteorological conditions were conducive factors. The number of December haze days over North China and the Huanghuai area has increased sharply since 2010 and was greatest in 2016. During 2016, the most aggressive control measures for anthropogenic emissions were implemented from 16 to 21 December, but the most severe haze pollution still occurred, covering approximately 25 % of the land area of China and lasting for 6 days. The atmospheric circulations must play critical roles in the sub-seasonal haze events. Actually, the positive phase of the East Atlantic–West Russia pattern in the middle troposphere strengthened the anomalous anti-cyclone over the NH area that confined vertical motion below. The associated southerly anomalies made the cold air and surface wind speed weaker, but enhanced the humid flow. Thus, the horizontal and vertical dispersion of atmospheric particulates was suppressed and the pollutants gathered within a narrow space. In December 2016, these key indices were strongly beneficial for haze occurrence and combined to result in the severest haze pollution. The influences of the preceding autumn sea surface temperature near the Gulf of Alaska and the subtropical eastern Pacific, October–November snow cover in western Siberia, and associated physical processes on haze pollution are also discussed.

Moisture and oily molecules stable nanofibrous electret membranes for effectively capturing PM 2.5

Abstract The fabrication of electret air filter with robust charge stability towards moisture and oily molecules is becoming increasingly essential due to the severe haze pollution, which is featured with high relative humidity (80–90%) and contains oily components (30–40%); however, this remains an ongoing challenge. Herein, a nanofibrous electret membrane able to enduringly capture PM 2.5 with high efficiency and low air resistance under the surroundings containing moisture and oily components is successfully designed via electrospinning. Benefiting from the high electrical resistivity of polyvinyl butyral (PVB) and high dielectric constant of silicon nitride nanoparticles (Si 3 N 4 NPs), PVB/Si 3 N 4 nanofibrous membranes are endowed with improved stable surface potentials from 1610 to 2010 V when the content of charge enhancer (Si 3 N 4 ) increases from 0 to 1 wt%. More importantly, the charge dissipating mechanism under water and oil condition is revealed. Moreover, by further introducing hydro-oleophobic fluorinated polyurethane (FPU), the stable surface potentials of PVB/Si 3 N 4 - FPU membranes are elevated by 62.8% under high relative humidity (85%) and 48.4% towards oily components, compared with PVB/Si 3 N 4 membranes. The resultant membranes achieve a high filtration efficiency of 99.950%, low air resistance of 55.0 Pa, and robust durability, providing a guidance for the design of electret air filtration materials used in haze environment.

Model elucidating the sources and formation mechanisms of severe haze pollution over Northeast mega-city cluster in China

Recent studies on regional haze pollution over China come up in general with strong variability of main causes of heavy polluted episodes, in linkage with local specificities, sources and pollution characteristics. This paper therefore aims at elucidating the main specific sources and formation mechanisms of observed strong haze pollution episodes over 1–15 November 2015 in Northeast region considered as one of biggest megacity clusters in China. The Northeast China mega-city cluster, including Heilong Jiang, Jilin and Liaoning provinces, is adjacent to Russia in the north, Mongolian at the west, North Korea at east, and representing key geographical location in the regional and transnational air pollution issues in China due to the presence of heavy industries and intense economic activities. The present study, based on air quality monitoring, remote sensing satellite data and sensitivity experiments carried on the Nested Air Quality Prediction Modeling System (NAQPMS), quantitatively assesses the impact of meteorological conditions and potential contributions from regional chemical transport, intensive energy combustion, illegal emission and biomass burning emissions to PM2.5 concentration variation. The results indicate strong inversion occurrence at lower atmosphere with weak near-surface wind speed and high relative humidity, leading to PM2.5 concentration increase of about 30–50%. Intensive energy combustion (plausibly for heating activities) and illegal emission also significantly enhance the overall PM2.5 accumulation by 100–200 μg m−3 (60–70% increase), against 75–100 μg m−3 from the biomass burning under the northeast-southwest transport pathway, corresponding to a contribution of 10–20% to PM2.5 concentration increase. Obviously, stagnant meteorological conditions, energy combustion, illegal emission and biomass burning are main drivers of strong haze formation and spatial distribution over Northeast China megacity cluster. In clear, much effort on emission abatement at both local and regional scales is still an urgent imperative to overcome current critical haze pollution.

A comparison of individual exposure, perception, and acceptable levels of PM2.5 with air pollution policy objectives in China

Atmospheric pollution has emerged as a major public health issue in China. Public perception and acceptable risk levels of air pollution can prompt individual behavioral changes and play a major role in the public’s response to health risks. Therefore, to explore these responses and evaluate what constitutes publicly acceptable concentrations of fine particulate matter (PM2.5), questionnaire surveys were conducted in three representative cities of China: Beijing, Nanjing, and Guangzhou. Great differences in public risk perception were revealed. Public perception of the health effects of air pollution (Effect) and familiarity with it (Familiarity) were significantly higher in the winter than in the summer, and also during severe haze days compared with typical days. The public perception of trust in the government (Trust) was consistent across all conditions. Exposure to severe haze pollution and experiencing harms from it were key factors influencing public willingness to respond to haze. These results reflected individual exposure levels correlating closely with risk perception and acceptance of PM2.5. However, a crucial gap exists between public acceptable risk levels (PARL) of air pollution and the policy objectives of the State Council’s Action Plan. Thus, policymakers can utilize this study to develop more targeted measures to combat air pollution.

Roles of regional transport and heterogeneous reactions in the PM2.5 increase during winter haze episodes in Beijing

Regional transport and chemical conversions are two major processes that lead to the severe haze pollution in China. Our observations during five haze episodes in Beijing between February 19 and March 12 of 2014 show that the two processes played different roles as PM2.5 increased from the clean (<75μgm−3) to the light-medium pollution level (75–150μg m-3) and to levels of heavy (150–250μgm−3) and severe (>250μgm−3) pollution. In the initial twelve hours of each episode, the PM2.5 reached the light-medium level with an increase of approximately 120μgm−3. At the same time, the particle (~10–700nm) number concentration also showed a distinct increase accompanied by a rapid increase in the mean diameter. A light-medium PM2.5 occurred in the south areas prior to the haze occurrence in Beijing and the southerly winds were predominant, indicating the rapid increase of PM2.5 in the initial stage was caused by the regional transport from the south. Subsequently, PM2.5 elevated to the heavy and severe levels when the wind was weak, relative humidity was high and ozone concentration was low. The increase of PM2.5 in the elevated stages was characterized by a high percentage (45% for the heavy level and 55% for the severe level) of secondary inorganic components, indicating the substantial contribution of the formation of secondary aerosols. In addition, the increases of the mean diameter (from 108nm to 120nm) and the total volume concentration (by 67%) are regarded as a consequence of heterogeneous reactions on the surfaces of aerosol particles because the particle number concentration remained nearly constant in these two stages. Our results indicate that, during the five winter haze episodes, the regional transport from the south was the major reason for the initial-stage PM2.5 increase, while heterogeneous reactions dominated the later elevation.

Cause and predictability for the severe haze pollution in downtown Beijing in November–December 2015

Based on the hourly PM2.5 concentrations, meteorological variable records and ERA-Interim reanalysis data, a series of diagnostic analyses were conducted to explore the possible meteorological causes for the severe haze pollution that occurred in Beijing in November–December 2015. Using the online-coupled WRF-Chem model and GFS data, the predictability of hourly and daily PM2.5 concentrations was evaluated. The results showed that, in the context of pollutant emission, the severe haze pollution in downtown Beijing in November–December 2015 was primarily attributed to anomalous local meteorological conditions, which were caused and strengthened by anomalous large-scale atmospheric circulations. The abnormal changes in the upper troposphere appeared to trigger the anomalies in the middle-lower troposphere and the local conditions. The numerical simulations can capture the spatial distribution patterns of the PM2.5 concentrations for predictions of 1 to 10days in advance. The PM2.5 concentration trends in downtown Beijing were generally consistent with the predictions on both daily and hourly time-scales, although the predictability decreased gradually as the lead times prolonged. The predictability of the daily mean PM2.5 concentration was slightly higher than that of the hourly concentration. The statistical indices suggested that the predictions of daily and hourly mean PM2.5 concentrations were generally skillful and reliable for maximum lead times of 8 and 5days, respectively.

Attributions of meteorological and emission factors to the 2015 winter severe haze pollution episodes in China's Jing-Jin-Ji area

Abstract. In the 2015 winter month of December, northern China witnessed the most severe air pollution phenomena since the 2013 winter haze events occurred. This triggered the first-ever red alert in the air pollution control history of Beijing, with an instantaneous fine particulate matter (PM2. 5) concentration over 1 mg m−3. Air quality observations reveal large temporal–spatial variations in PM2. 5 concentrations over the Beijing–Tianjin–Hebei (Jing-Jin-Ji) area between 2014 and 2015. Compared to 2014, the PM2. 5 concentrations over the area decreased significantly in all months except November and December of 2015, with an increase of 36 % in December. Analysis shows that the PM2. 5 concentrations are significantly correlated with the local meteorological parameters in the Jing-Jin-Ji area such as the stable conditions, relative humidity (RH), and wind field. A comparison of two month simulations (December 2014 and 2015) with the same emission data was performed to explore and quantify the meteorological impacts on the PM2. 5 over the Jing-Jin-Ji area. Observation and modeling results show that the worsening meteorological conditions are the main reasons behind this unusual increase of air pollutant concentrations and that the emission control measures taken during this period of time have contributed to mitigate the air pollution ( ∼ 9 %) in the region. This work provides a scientific insight into the emission control measures vs. the meteorology impacts for the period.

A dark October in Beijing 2016

AbstractIn recent years, haze pollution events in Beijing have increased sharply, and the haze pollution of Beijing in October 2016 reached a new high. Meteorological conditions are thought to have influences on the haze occurrence, yet the associated atmospheric circulation of haze in October and why the most severe haze pollution occurred in 2016 is still unclear. Here, the authors show through daily observation and reanalysis data that key regions of North Atlantic and North Pacific sea surface temperature (SST) anomalies may be the main factors for this most severe haze event. Since 2013, the SSTs of these two key regions have increased dramatically and reached a peak, which could have induced the severe haze pollution by affecting the Eurasia teleconnection (EU) and the North Pacific Oscillation, with these factors then providing favorable dynamic and thermodynamic conditions for haze development.

Characterization of black carbon in an urban-rural fringe area of Beijing

Measuring black carbon (BC) is critical to understand the impact of combustion aerosols on air quality and climate change. In this study, BC was measured in 2014 at a unique community formed with rapid economic development and urbanization in an urban-rural fringe area of Beijing. Hourly BC concentrations were 0.1–33.5 μg/m3 with the annual average of 4.4 ± 3.7 μg/m3. BC concentrations had clear diurnal, weekly, and seasonal variations, and were closely related with atmospheric visibility. The absorption coefficient of aerosols increased while its contribution to extinction coefficient decreased with the enhancement of PM2.5 concentration. The high mass absorption efficiency (MAE) of EC was attributed to a combination of coal combustion, vehicular emission and rapidly coating by water-soluble ions and organic carbon (OC). BC concentrations followed a typical lognormal pattern, with over 88% samples in 0.1–10.0 μg/m3. Low BC levels were mostly bounded up with winds from north and northwest. Coal combustion and biomass burning were closely associated with severe haze pollution events. Firework discharge had significant UV absorption contribution. During the Asia-Pacific Economic Cooperation (APEC) forum in November 2014, air quality obviously improved due to various control strategies.

Predicting household PM2.5-reduction behavior in Chinese urban areas: An integrative model of Theory of Planned Behavior and Norm Activation Theory

Fine particulate matter (PM2.5) emissions have attracted wide attention due to their negative effects on haze air pollution and human health. Regulating household PM2.5-reduction behavior is a beneficial measure for PM2.5 emission control in urban areas. The current research examines the determinants that affect household PM2.5-reduction behavioral intention, and an integrative model of Theory of Planned Behavior (TPB), incorporated with Norm Activation Theory (NAM), was used. An effective sample of 418 urban households who lived in heavy haze areas of China was collected. The empirical results revealed that household attitude toward PM2.5-reduction, perceived behavioral control and descriptive norm all significantly affected PM2.5-reduction intention, while subjective norm was not. Furthermore, in addressing severe haze pollution, household environmental concern indirectly and significantly affects their moral norm and intention. In addition, there was a moderating effect of perceived behavioral control (stemming from TPB) on the relationship between household moral norm (stemming from NAM) and PM2.5-reduction intention. The results confirm the appropriateness of the integrative model in predicting household intention to participate in PM2.5-reduction behavior. Then, we discuss the implications for regulating household PM2.5-reduction behavior based on the determinants and provide suggestions for future studies.

Characterization of chemical compositions in size-segregated atmospheric particles during severe haze episodes in three mega-cities of China

To investigate the characterization of chemical compositions in size-segregated particles during severe haze pollution episodes in different regions of China, a campaign was conducted in Tianjin, Hangzhou and Chengdu. Size-segregated particles were collected with eight-stage Anderson cascade impactor in these cities in winter respectively. Ten major compositions of particles including (Na+, NH4+, K+, Mg2+, Ca2+, Cl−, NO3−, SO42−, OC and EC) were analyzed. A similar bimodal distribution of particles was found between northern and southern cities peaked at 0.7–2.1 and 9.0–10.0μm. OC, EC, SO42−, NO3−, Cl− and NH4+ were the major chemical compositions of fine-mode particles, whereas OC, EC, SO42−, NO3− and Ca2+ were the major compositions of coarse-mode particles. In the three cities, Cl−, SO42−, NO3−, NH4+ and K+ of all compositions were unimodal distributions peaked at 0.7–2.1μm. Different sources to particles in the three cities were inferred based on the size distribution characteristics of chemical compositions. For Tianjin, the influence of sea salt was greater to Hangzhou and Chengdu based on the concentrations and distributions of Na+ and the Cl−. Fine-mode Cl− and SO42− were highest in Tianjin, meaning the greater contribution of coal burning to particles during severe pollution. For Hangzhou, the NO3− concentration was higher than Tianjin and Chengdu. Contribution of nitrate to PM was higher than that of sulfate. For Chengdu, carbonaceous species contributed mostly to fine particles. However, sulfate and nitrate contributed mostly to fine particles in Tianjin and Hangzhou. The contributions of EC and Ca2+ to coarse-mode particles was much higher than that in other cities, implying the greater influence of soil particles, construction dust or falling dust to PM in Chengdu. In addition, there were greater emission source of NH4+ in Chengdu. Northwest, west and southeast were the major transport pathways of air masses for Tianjin, Hangzhou and Chengdu.

Reactive nitrogen chemistry in aerosol water as a source of sulfate during haze events in China.

Fine-particle pollution associated with winter haze threatens the health of more than 400 million people in the North China Plain. Sulfate is a major component of fine haze particles. Record sulfate concentrations of up to ~300 μg m-3 were observed during the January 2013 winter haze event in Beijing. State-of-the-art air quality models that rely on sulfate production mechanisms requiring photochemical oxidants cannot predict these high levels because of the weak photochemistry activity during haze events. We find that the missing source of sulfate and particulate matter can be explained by reactive nitrogen chemistry in aerosol water. The aerosol water serves as a reactor, where the alkaline aerosol components trap SO2, which is oxidized by NO2 to form sulfate, whereby high reaction rates are sustained by the high neutralizing capacity of the atmosphere in northern China. This mechanism is self-amplifying because higher aerosol mass concentration corresponds to higher aerosol water content, leading to faster sulfate production and more severe haze pollution.

Characterizing PM2.5 in Beijing and Shanxi Province using terahertz radiation

Particles of aerodynamic diameter⩽2.5 μm (PM2.5) caused extremely severe and persistent haze pollution is of concern in many cities. In this study, samples of PM2.5 were collected from atmosphere environment of Beijing and Shanxi Province, and analyzed using terahertz (THz) radiation. The transmission spectrum of PM2.5 in Shanxi Province had two distinct absorption peaks at 6.0 and 6.7 THz, and the curve was increasing on the whole. However, the transmission spectrum of PM2.5 in Beijing had obviously different variation tendency and the absorption peak was studied by monitoring PM2.5 masses in conjunction with two-dimensional correlation spectroscopy (2DCOS). By comparing the pollutant species and concentrations of Shanxi Province and Beijing over the time of collecting samples, the concentrations of sulfate and ammonium were similar, which contributed to emerge absorption bands in the same position. While the concentrations of organic matter (OM), nitrate, chloride and elemental carbon (EC) were different. Furthermore, dust and some other inorganic ion are unique to Shanxi province, which lead to different variation tendency of the transmission spectrum of PM2.5. These results will be of importance for environmental monitoring and for controlling PM emissions. According to this research, optical techniques, and especially spectral methods, should be considered for PM2.5 monitoring.

Modeling analysis of secondary inorganic aerosols over China: pollution characteristics, and meteorological and dust impacts.

Secondary inorganic aerosols (SIA) are the predominant components of fine particulate matter (PM2.5) and have significant impacts on air quality, human health, and climate change. In this study, the Community Multiscale Air Quality modeling system (CMAQ) was modified to incorporate SO2 heterogeneous reactions on the surface of dust particles. The revised model was then used to simulate the spatiotemporal characteristics of SIA over China and analyze the impacts of meteorological factors and dust on SIA formation. Including the effects of dust improved model performance for the simulation of SIA concentrations, particularly for sulfate. The simulated annual SIA concentration in China was approximately 10.1 μg/m3 on domain average, with strong seasonal variation: highest in winter and lowest in summer. High SIA concentrations were concentrated in developed regions with high precursor emissions, such as the North China Plain, Yangtze River Delta, Sichuan Basin, and Pearl River Delta. Strong correlations between meteorological factors and SIA pollution levels suggested that heterogeneous reactions under high humidity played an important role on SIA formation, particularly during severe haze pollution periods. Acting as surfaces for heterogeneous reactions, dust particles significantly affected sulfate formation, suggesting the importance of reducing dust emissions for controlling SIA and PM2.5 pollution.

High molecular weight organic compounds (HMW-OCs) in severe winter haze: Direct observation and insights on the formation mechanism

High molecular weight organic compounds (HMW-OCs), formed as secondary organic aerosols (SOA), have been reported in many laboratory studies. However, little evidence of HMW-OCs formation, in particular during winter season in the real atmosphere, has been reported. In January 2013, Beijing faced historically severe haze pollution, in which the hourly PM2.5 concentration reached as high as 974 μg m−3. Four typical haze events (HE1 to HE4) were identified, and HE2 (Jan. 9–16) was the most serious of these. Based on the hourly observed chemical composition of PM2.5 and the daily organic composition analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS), we found that abundant ion peaks in m/z 200–850 appeared on heavy haze days, whereas these were negligible on a clear day, indicating the existence of HMW-OCs in the wintertime haze. A negative nonlinear correlation between HMW-OCs and O3 suggested that gas oxidation was not likely to be the dominant mechanism for HMW-OCs formation. During the heavy haze events, the relative humidity and mass ratio of H2O/PM2.5 reached as high as 80% and 0.2, respectively. The high water content and its good positive correlation with HMW-OCs indicated that an aqueous-phase process may be a significant pathway in wintertime. The evidence that acidity was much higher during HE2 (0.37 μg m−3) than on other days, as well as its strong correlation with HMW-OCs, indicated that acid-catalyzed reactions likely resulted in HMW-OCs formation during the heavy winter haze in Beijing.

Surface charges on aerosol particles – Accelerating particle growth rate and atmospheric pollution

Many Chinese mega-cities frequently experienced severe and persistent haze pollution in recent years. Especially, the so-called ‘explosive growth’ of PM2.5 concentration has often been observed at the beginning of a severe pollution event in winter. As shown in Figure 1(a), the explosive growth of PM2.5 concentration could be increased from below 50 mg/m up to 250 mg/m in only 5–10 h. The explosive growth of PM2.5 concentration in cities can have a strong impact on people’s life and health. In contrast, in Figure 1(b), during 1–5 November 2013 in winter, the PM2.5 mass concentration grew accumulatively in Xi’an, increasing the concentration from 23 to 137 mg/m. Meanwhile, the speed of coagulation of new particles in these PM2.5 concentrations during the explosive growth event is evidently far more than the speed of normal accumulation of these PM2.5 concentrations as shown in Figure 1(b) and with long duration. Although many scholars have put forward ideas to analyse the pollution of high PM2.5 concentration from various directions, the details and theory of particulate explosive growth process are still not clearly defined and elucidated. Secondary reactions may have contributed to the increment growth of particle number concentration, but the high speed of chemical reaction is confusing the possible theory. Actually, at the beginning of a severe haze, the process of explosive growth of PM2.5 concentration could be undergoing a series of physical–chemical processes, in which the charging particles have a significant influence. The charges and ions on particle surfaces could affect the collision and coagulation behaviour of particles, and also the subsequent chemical reactions occurring on the particle porous surfaces. Aerosols in any form are usually electrically charged, no matter in solid, air or liquid (including cloud aerosol, fog aerosol and smog aerosol), either in natural or artificial form. There are many natural or artificial factors that could charge the aerosol particles, such as cosmic rays in space, radiation from radioactive material in air and on earth, atmospheric lightning, electromagnetic radiation, high temperature discharge and static electricity caused by particles collision. On the other hand, because fine particles are porous media with rough surfaces, changeable shapes and uneven energy distribution on surfaces, the distribution of ions and electrical charges on particle surfaces must be uneven, and the energy would gather at the location with small curvature. Thus, the high potential and electrical charges could easily aggregate at the cusp. When a fine particle is separated from a larger particle, a static charge transfer would arise giving two charged particles. Particles with different diameters would become charged after their collision and then separate from each other. When aerosol particles are carrying electrical charges, particle interactions and surface chemical reactions could be affected by these surface charges, thus changing some physical characteristics of particles, such as cohesion, adhesion and its stability in the atmosphere. The electron dynamics of these charged particles could also have an adverse effect on human’s health. The recent research suggested that during the process of explosive growth, the reverse growth of volume concentration of aerosol may be influenced by fluctuation of air moisture under stable atmospheric conditions, which means that in a very short period of time, under the condition of stable or declining number concentration of aerosol particles, adsorbing moisture could increase the diameter of aerosols. In fact, water molecules adsorbed on the surface of particles in atmospheric environment could play a very complicated role in the process of particles collision. If thin water film is present on the surfaces of suspended aerosol particles, a ‘water bridge’ could be formed at the contact interface when particles are moving and colliding in the air, by which hydrogen ions would be

Causation mechanism analysis for haze pollution related to vehicle emission in Guangzhou, China by employing the fault tree approach

Recently, China has frequently experienced large-scale, severe and persistent haze pollution due to surging urbanization and industrialization and a rapid growth in the number of motor vehicles and energy consumption. The vehicle emission due to the consumption of a large number of fossil fuels is no doubt a critical factor of the haze pollution. This work is focused on the causation mechanism of haze pollution related to the vehicle emission for Guangzhou city by employing the Fault Tree Analysis (FTA) method for the first time. With the establishment of the fault tree system of “Haze weather—Vehicle exhausts explosive emission”, all of the important risk factors are discussed and identified by using this deductive FTA method. The qualitative and quantitative assessments of the fault tree system are carried out based on the structure, probability and critical importance degree analysis of the risk factors. The study may provide a new simple and effective tool/strategy for the causation mechanism analysis and risk management of haze pollution in China.

Aerosol characterization over the North China Plain: Haze life cycle and biomass burning impacts in summer

AbstractThe North China Plain experiences frequent severe haze pollution during all seasons. Here we present the results from a summer campaign that was conducted at Xianghe, a suburban site located between the megacities of Beijing and Tianjin. Aerosol particle composition was measured in situ by an Aerosol Chemical Speciation Monitor along with a suite of collocated measurements during 1–30 June 2013. Our results showed that aerosol composition at the suburban site was overall similar to that observed in Beijing, which was mainly composed of organics (39%), nitrate (20%), and sulfate (18%). Positive matrix factorization of organic aerosol (OA) identified four OA factors with different sources and processes. While secondary organic aerosol dominated OA, on average accounting for 70%, biomass burning OA (BBOA) was also observed to have a considerable contribution (11%) for the entire study period. The contribution of BBOA was increased to 21% during the BB period in late June, indicating a large impact of agricultural burning on air pollution in summer. Biomass burning also exerted a significant impact on aerosol optical properties. It was estimated that ~60% enhancement of absorption at the ultraviolet spectral region was caused by the organic compounds from biomass burning. The formation mechanisms and sources of severe haze pollution episodes were investigated in a case study. The results highlighted two different mechanisms, i.e., regional transport and local sources, driving the haze life cycles differently in summer in the North China Plain. While secondary aerosol species dominated aerosol composition in the episode from regional transport, organics and black carbon comprised the major fraction in the locally formed haze episode.

Possible influence of atmospheric circulations on winter haze pollution in the Beijing–Tianjin–Hebei region, northern China

Abstract. Using the daily records derived from the synoptic weather stations and the NCEP/NCAR and ERA-Interim reanalysis data, the variability of the winter haze pollution (indicated by the mean visibility and number of hazy days) in the Beijing–Tianjin–Hebei (BTH) region during the period 1981 to 2015 and its relationship with the atmospheric circulations at middle–high latitude were analyzed in this study. The winter haze pollution in BTH had distinct inter-annual and inter-decadal variabilities without a significant long-term trend. According to the spatial distribution of correlation coefficients, six atmospheric circulation indices (I1 to I6) were defined from the key areas in sea level pressure (SLP), zonal and meridional winds at 850 hPa (U850, V850), geopotential height field at 500 hPa (H500), zonal wind at 200 hPa (U200), and air temperature at 200 hPa (T200), respectively. All of the six indices have significant and stable correlations with the winter visibility and number of hazy days in BTH. In the raw (unfiltered) correlations, the correlation coefficients between the six indices and the winter visibility (number of hazy days) varied from 0.57 (0.47) to 0.76 (0.6) with an average of 0.65 (0.54); in the high-frequency ( &lt; 10 years) correlations, the coefficients varied from 0.62 (0.58) to 0.8 (0.69) with an average of 0.69 (0.64). The six circulation indices together can explain 77.7 % (78.7 %) and 61.7 % (69.1 %) variances of the winter visibility and the number of hazy days in the year-to-year (inter-annual) variability, respectively. The increase in Ic (a comprehensive index derived from the six individual circulation indices) can cause a shallowing of the East Asian trough at the middle troposphere and a weakening of the Siberian high-pressure field at sea level, and is then accompanied by a reduction (increase) of horizontal advection and vertical convection (relative humidity) in the lowest troposphere and a reduced boundary layer height in BTH and its neighboring areas, which are favorable for the formation of haze pollution in BTH winter, and vice versa. The high level of the prediction statistics and the reasonable mechanism suggested that the winter haze pollution in BTH can be forecasted or estimated credibly based on the optimized atmospheric circulation indices. Thus it is helpful for government decision-making departments to take action in advance in dealing with probably severe haze pollution in BTH indicated by the atmospheric circulation conditions.