Air Pollution Dispersion Research Articles

Evaluation of the impact of the national strike of the road freight transport sector on the air quality of the metropolitan region of Rio de Janeiro, Brazil

In May 2018, there was a road freight transport standstill in Brazil that lasted 11 days. During this period, several impacts on Rio de Janeiro’s daily life were reported, such as the reduction of road passenger transport services and lack of fuels. This study aimed to evaluate the impact on the air quality of the metropolitan region of Rio de Janeiro (MRRJ) of the reduction of heavy-duty vehicles on the streets and roads. For this purpose, the reductions of PM10, NOx, SOx and CO emissions, due to low circulation of buses and trucks, were estimated in order to assess the levels of air pollution indirectly. Besides, air quality data (PM10, NO2, SO2, and CO) monitored before and during the strike were used. The results showed a reduction in total emissions of local air pollutants, harmful to human health from 22 % to 43 % during strike days. However, the air quality reflexes were not observed in the same proportion, on the contrary, increases were observed in pollutant concentrations in the atmosphere during traffic stoppage in the study areas, due to different weather conditions in the two periods, which directly influenced air pollutants dispersion.

Exposure to particulate matter and risk of conversion from mild cognitive impairment to dementia: a cohort study in a Northern Italy population

Background/Aim Exposure to air pollutants such as inhalable particulate matter has been linked to increased risk of chronic disease including neurodegenerative diseases, such as Alzheimer’s dementia. In this study, we aimed to evaluate the effect of long-term exposure to outdoor air pollution, and specifically to particulate matter ≤10 μm (PM10), on the risk of dementia in a cohort of subjects with mild cognitive impairment. MethodsWe recruited 53 subjects newly-diagnosed with mild cognitive impairment of non-vascular origin and residing in the Modena and Reggio Emilia provinces of Northern Italy. Using a Geographical Information System and a validated air pollution dispersion model, we assessed exposure to outdoor PM10 from motorized traffic at subjects’ residence. We investigated the relation of these concentrations to subsequent onset of dementia, using a Cox proportional hazards model. We computed hazard ratio (HR) and 95% confidence interval (CI) according to fixed categories of PM10 exposure, adjusting for sex, age, and educational attainment level. ResultsDuring a median follow-up of 42 months, 19 participants developed Alzheimer’s dementia, 3 frontotemporal dementia and 2 Lewy body dementia. Baseline PM10 exposure levels were 9.6 µg/m3 on average. Using PM10 levels below 5 µg/m3 as reference, we found a dose-response increase in any dementia risk with HR of 1.04 (95% CI 0.41-2.66) at 5-10 µg/m3, 1.32 (95% CI 0.36-4.92) at 10-20 µg/m3, and 1.38 (95% CI 0.14-13.13) above 20 µg/m3, respectively. Conclusions Our results suggest that exposure to particulate matter emitted by motorized vehicles increases the risk of conversion from mild cognitive impairment to dementia, though the low number of study participants suggests caution in the interpretation of these findings.

Association between long-term exposure to air pollution and ambient noise with altered resting-state brain connectivity in the 1000BRAINS study

Background/Aim: Long-term air pollution (AP) is associated with cognitive impairment and altered brain structure. These changes are also observed during normal aging. Studies in younger children additionally hint at an age-related functional brain reorganization, i.e. reduced resting-state functional connectivity (RSFC) within functional brain networks and increased RSFC between different brain networks. The current study examined the associations between long-term AP and ambient noise (AN) with RSFC reorganization in older adults.Methods: We used data from participants of the German 1000BRAINS study. To measure AP at the participant’s residences for the years 2000-2003, we applied land use regression and spatiotemporal European Air Pollution Dispersion Chemistry Transport modeling. Exposure to AN was modeled as weighted 24-h (LDEN) means and night-time (LNIGHT) means. Between 2011 and 2015, resting-state functional imaging brain scans were acquired. We defined seven resting-state brain networks (RSN): visual, sensorimotor, dorsal- and ventral attention, limbic, frontoparietal and default RSN and evaluated the degree of segregation as the ratio of within-network RSFC and inter-network RSFC. Multiple linear regression models adjusted for age, sex, socioeconomic status and lifestyle variables were used to estimate the relationship of AP and AN with RSFC.Results: The analysis included 583 participants (44.1% female, mean age of 56 years). Overall, clearly decreased segregation patterns were not visible. Weak associations of particular matter (PM2.5), soot and particle number concentration with decreased segregation were observed in the sensorimotor RSN (i.e. 0.088 [95%-Confidence-Interval: -0.170; -0.006] per 1.41 µg/m3 increase in PM2.5). For a 10 dB(A) increase of LDEN and LNIGHT, we observed weak decreases in segregation of the visual RSN.Conclusions: In accordance with major aging theories, higher exposure to AP and AN could possibly lead to an acceleration of age-related functional brain reorganization. To verify these findings, further studies with larger sample size are needed.

Long-term Exposure to Low Concentration of PM2.5 and Mortality: A Danish Nurse Cohort Study

Background/Aim. The association between air pollution and mortality is well established, yet studies in areas with low levels of air pollution, below EU limit values, with adjustment for road traffic noise, are sparse. We examined the association of long-term exposure to fine particulate matter (PM2.5) with mortality due to cardiovascular disease (CVD), respiratory disease (RD), and diabetes as well as all-cause natural mortality.Methods. We used data on 24,541 female nurses from the Danish Nurse Cohort who, at recruitment in 1993 or 1999, reported information on risk factors. Data on death were obtained from the Danish Register of Causes of Death until the end of 2013. Annual mean concentrations of PM2.5 in 1990-2013 at the nurses’ residences were estimated using the Danish air pollution dispersion modeling system. We examined associations between the 3-year running mean of PM2.5 with all-cause natural and cause-specific mortality by using time-varying Cox Regression models, adjusting for individual characteristics.Results. During the study time-period, 3,708 nurses died, and of these, 843 were due to CVD, 310 due to RD, and 64 due to diabetes. The mean level of PM2.5 at the baseline was 20.5 µg/m3. In the fully adjusted models, including road traffic noise, we found positive associations of 3-year running mean of PM2.5 with all-cause natural (hazard ratio; 95% confidence interval: 1.06; 1.01-1.11), CVD (1.14; 1.03-1.26), and diabetes mortality (1.41; 1.05-1.90), per interquartile range of 4.39 μg/m3. In subjects exposed to low levels of PM2.5 (< 20 µg/m3), we found even stronger association with all-cause natural (1.19; 1.11-1.27), CVD (1.27; 1.01-1.46), RD (1.27; 1.00-1.60), and diabetes mortality (1.44; 0.83-2.48).Conclusion. In a Danish cohort of female nurses, long-term exposures to low-levels of PM2.5 were associated with all-cause mortality, strongest for diabetes, and CVD, which persisted at the levels below the current EU limit values.

Application of Bayesian networks for accuracy estimation of modeling results of the air pollution dispersion given inaccurate input data

The article deals with estimating the results accuracy of the modeling of air pollution dispersion when introducing inaccurate input data. Restrictions on accuracy estimation methods for Ukraine are considered. It is suggested to use Bayesian networks with discrete input variables to obtain the estimates. The structure of the network is presented, and the methods of filling the probability tables are proposed.

Characterization of Urban Greening in a District of Lecce (Southern Italy) for the Analysis of CO2 Storage and Air Pollutant Dispersion

This paper is devoted to the assessment of urban greening effects on two important ecosystem services, i.e., air quality and CO2 storage, including the corresponding economic impacts in a real urban area, i.e., a district located in the Mediterranean city of Lecce (southern Italy). Two tools were employed, i-Tree Canopy and the computational fluid dynamics (CFD) microclimate model ENVI-met. i-Tree Canopy allowed fully determining the land-cover percentage on the basis of different ground cover classes and obtaining an estimate of annual values of CO2 storage, air pollutant removal, and economic benefits in the presence of urban greening. The estimate in i-Tree Canopy considered only the amount of greening; therefore, air pollutant removal estimates were only potential. As the vegetation was located in street canyons, its interaction with local meteorology and urban geometry strictly affected the dispersion of nitrogen oxides (NOx) (taken here as an example) as obtained from ENVI-met simulations. In ENVI-met, both deposition/absorption and aerodynamic effects were considered, and local increases in concentration were found in the district. The analysis of results obtained from different tools (one complex (CFD model) and the other simple (i-Tree model)) showed the error associated with the simple model in the computation of impacts if the interaction among the vegetation characteristics, the meteorological conditions, and the urban geometry was neglected; however, it also uncovers a novel approach for comprehensively characterizing a given area in terms of its vegetation cover, CO2 storage, and economic benefits, as well as local effects on air quality. This study is set in a broader context aimed at assessing the air quality in urban canopies of Mediterranean areas characterized by the presence of narrow street canyons where pollutants can accumulate due to ineffective air exchange with the above atmosphere.

Analysis of the urban heat island under different synoptic patterns using local climate zones

Characterising the spatio-temporal variability of the Urban Heat Island intensity (UHII) is of utmost importance to understand processes related to air pollution dispersion and thermal comfort. However, this feature is still under-researched in most global cities due to instrument limitations or lack of expertise. This study aims at investigating the influences of standard and subclasses of Local Climate Zones (LCZ) on the behaviour of the UHI in a Brazilian city, using LCZs classification/sub-classification and in situ near-surface air temperature observations. Cluster analysis applied to daily meteorological data split the study period into five groups with similar weather characteristics. Each cluster was dominated by a combination of weather systems acting over the region which, in turn, determined the strength of the UHII. The overall diurnal UHII was strong during the nights and early mornings, with mean maximum values of 6.0 °C, and around 0 °C or negative during the rest of the day. The largest UHII (11.0 °C) was registered under anticyclone conditions, whilst the smallest ones (around 0 °C) were always observed under overcast and rainy conditions regulated by the passage of troughs, cold fronts and mesoscale complex systems. The spatial distribution of the nocturnal UHII based on the sampled and predicted LCZ temperature analysis showed that the central areas were substantially warmer than the suburban and rural areas. The introduction of six LCZ sub-classes revealed to be a suitable mapping approach to describe the land use and cover and evaluate the air temperature field in areas with mixed urban fabric . The LCZ map helped identify key climatic areas which could be used in planning strategies to target the UHI effects and create both aesthetically pleasant and healthy cities.

In Defense of the Weight-of-Evidence Approach to Literature Review in the Integrated Science Assessment

In Defense of the Weight-of-Evidence Approach to Literature Review in the Integrated Science Assessment

Source apportionment of black carbon and the feedback effect on the meteorological factors in Beijing, China.

Black carbon (BC) is a major light-absorbing component in the atmosphere and plays an important role in aerosol radiative forcing. In this study, the combination of monitoring data and the WRF-Chem model was used to study the source apportionment of BC in China during January 2017. Meanwhile, the aerosol-radiation interaction (ARI) effect of BC was also simulated. We found that the average BC/PM2.5 ratios were 4.8%, 4.2%, and 3.8% in Shijiazhuang, Tangshan, and Beijing, respectively. The source apportionment suggested that traffic emissions played a dominant role in the BC concentration over Beijing. The traffic, residential, industrial, and power contributions accounted for 41%, 32%, 25%, and 2% of total concentration, respectively. The BC concentration in Beijing was also affected by regional transport. During January, the contributions of monthly regional transport to BC and PM2.5 concentrations in Beijing were 41% and 49%, respectively. BC emissions decreased downward shortwave radiation (SWDOWN) at the surface, leading to a decrease in temperature. As a result, the planetary boundary layer height (PBLH) development was suppressed and the relative humidity increased. The stable meteorological conditions suppressed the dispersion of air pollutants and increased BC concentrations. Traffic emissions decreased the monthly SWDOWN by approximately 2.2W/m2, decreased 2m temperature (T2) by approximately 0.1°C, increased 2m relative humidity (RH2) by approximately 0.5%, and decreased PBLH by approximately 4.4m.

Airflow Characteristics Downwind a Naturally Ventilated Pig Building with a Roofed Outdoor Exercise Yard and Implications on Pollutant Distribution

The application of naturally ventilated pig buildings (NVPBs) with outdoor exercise yards is on the rise mainly due to animal welfare considerations, while the issue of emissions from the buildings to the surrounding environment is important. Since air pollutants are mainly transported by airflow, the knowledge on the airflow characteristics downwind the building is required. The objective of this research was to investigate airflow properties downwind of a NVPB with a roofed outdoor exercise yard for roof slopes of 5°, 15°, and 25°. Air velocities downwind a 1:50 scaled NVPB model were measured using a Laser Doppler Anemometer in a large boundary layer wind tunnel. A region with reduced mean air velocities was found along the downwind side of the building with a distance up to 0.5 m (i.e., 3.8 times building height), in which the emission concentration might be high. Additional air pollutant treatment technologies applied in this region might contribute to emission mitigation effectively. Furthermore, a wake zone with air recirculation was observed in this area. A smaller roof slope (i.e., 5° slope) resulted in a higher and shorter wake zone and thus a shorter air pollutant dispersion distance.

Mathematical Model in Air Pollution with Area Source

A steady state two-dimensional atmospheric advection- diffusion numerical model of area source air pollution is presented. This model takes into account the actual form of variable settling velocity and eddy-diffusivity profile. Here the influence of settling velocity must be taken into account for the study of atmosphere dispersion. Therefore in the present analysis the two dimensional steady state dispersion of air pollutants over an area source under the settling effect has been investigated. The results obtained are compared with the known results and are found in close agreement.

Major air pollutants seasonal variation analysis and long-range transport of PM10 in an urban environment with specific climate condition in Transylvania (Romania)

The air quality decrease, especially in urban areas, is related to local-scale conditions and to dispersion of air pollutants (regional and long-range) as well. The main objective of this study was to decipher the seasonal variation of PM10, NO, NO2, NOx, SO2, O3, and CO over a 1-year period (2017) and the possible relationships between air pollution and meteorological variables. Furthermore, trajectory cluster analysis and concentration-weighted trajectory (CWT) methods were used to assess the trajectories and the source-receptor relationship of PM10 in the Ciuc basin Transylvania, known as the “Cold Pole” of Romania. The pollutants show lower concentrations during warmer periods, especially during summer, and significantly higher concentrations were observed on heating season in winter due to seasonal variations in energy use (biomass burning) and atmospheric stability. Subsequently, in February, the highest concentration of PM10 was 132 μg/m3, which is 4 times higher than the highest recorded monthly mean. Our results indicate a negative correlation between CO/temperature (− 0.89), NOx/temperature (− 0.84) and positive between NOx/PM10 (0.95), CO/PM10 (0.9), and NOx/CO (0.98), respectively. Dominant transport pathways were identified and the results revealed that slow-moving southerly (~ 45%) and northwesterly (~ 32%) air masses represent almost 80% and mainly regional flows were discerned. During 2017, increased PM10 levels were measured at the study site when air masses arrived mostly from northwest and southeast. The CWT and polarplot models show a strong seasonal variation and significant differences were observed between weekdays and weekends, namely highest PM10 concentrations during weekends at low wind speed (2–4 m/s).

Air Pollution Dispersion Modeling in Port Areas

For the last couple of decades, environmental protection awareness within port areas is gaining ever more importance. Ports can have a tremendous impact on the environment, especially in terms of air pollution. The main pollution sources are various port activities such as road and rail traffic, cargo handling and marine vessel operations. Air quality models can be of great help in estimating the effect on the ambient air quality from one or more sources emitting pollutants to the atmosphere. One of those models is the widely used Gaussian Plume dispersion approach. Based on existing measurements and port activity data, models can simulate the dispersion of air pollutants caused by activities and operations taking place within the port. By using historical data, they can simulate the current state of the air quality in the port and with the help of weather predictions simulate possible future situation. Simulations can assist the port manager/operator in the decision-making process in order to optimize various activities within the port and minimize their impact on the environment. One of the main objectives of the Horizon 2020 Project PIXEL (Port IoT for environmental leverage) is the deployment of environmental pollution models which can aid in the decision-making processes within the port domain. This paper reviews the current advances in the field of air pollution modelling with a special emphasis on port scenarios.

Boundary Layer Height as Estimated from Radar Wind Profilers in Four Cities in China: Relative Contributions from Aerosols and Surface Features

The turbulent mixing and dispersion of air pollutants is strongly dependent on the vertical structure of the wind, which constitutes one of the major challenges affecting the determination of boundary layer height (BLH). Here, an adaptive method is proposed to estimate BLH from measurements of radar wind profilers (RWPs) in Beijing (BJ), Nanjing (NJ), Chongqing (CQ), and Wulumuqi (WQ), China, during the summer of 2019. Validation against simultaneous BLH estimates from radiosondes (RSs) yielded a correlation coefficient of 0.66, indicating that the method can be used to derive BLH from RWPs. Diurnal variations of BLH and the ventilation coefficient (VC) at four sites were then examined. A distinct diurnal cycle of BLH was observed over all four cities; BLH gradually increased from sunset, reached a maximum in the afternoon, and then dropped sharply after sunset. The maximum hourly average BLH (1.426 ± 0.46 km) occurred in WQ, consistent with the maximum hourly mean VC larger than 5000 m2/s observed there. By comparison, the diurnal variation of VC was not strong, with values ranging between 2000 and 3000 m2/s, likely owing to the high-humidity environment. Furthermore, surface sensible heat flux, latent heat flux, and dry mass of particulate matter with aerodynamic diameter ≤2.5 µm (PM2.5) concentrations were found to somehow affect the vertical structure of wind and thermodynamic features, leading to a difference between RS and RWP BLH estimates. This indicates that the atmospheric environment can affect BLH estimates using RWP data. The BLH results from RWPs were better in some specific cases. These findings show great potential of RWP measurements in air quality research, and will provide key data references for policy-making toward emission reductions.

Wind-tunnel measurements and LES simulations of air pollutant dispersion caused by fire-induced buoyancy plume inside two parallel street canyons

A physical model consisting of two parallel street canyons with the fire room located in the windward side of the first street canyon was established. Large eddy simulation (LES) was employed to investigate the effects of air pollutant dispersion caused by the fire-induced buoyancy plume on the indoor and outdoor air quality. The effect of thermal buoyancy was firstly taken into account by burning the smoke cakes in wind-tunnel experiments under different Fr (Froude number) cases. Results show that the diffusion characteristics of smoke plume, temperature and velocity distributions by wind-tunnel measurements agreed well with the numerical models. According to the smoke soot’s effects on two street canyons, the dispersion of fire pollutants can be divided into three regimes. There exist two critical Fr, Frcrit,1=0.313 and Frcrit,2=0.389, at which the smoke plume begins to influence the 1st and 2nd street canyons, respectively. Moreover, the region areas of w < 0 (vertical velocity) can indirectly represent the concentration distribution of pollutants, and the temperature distribution is closely proportional to the distribution of pollutant (smoke plume, CO2 and CO) concentration, that is, where the plume concentration is high, the temperature is high. The quantitative formulas between Ucrit (Ucrit,1 and Ucrit,2) and the reference height (Zref) of the fire source at different floors were further confirmed. This study provides a new idea for visualizing the diffusion characteristics of fire pollutants, and is helpful for dealing with the building fire, personnel evacuation and emergency escape.

Numerical Modeling for the Accidental Dispersion of Hazardous Air Pollutants in the Urban Metropolitan Area

A numerical simulation system is developed to predict the dispersion of hazardous air pollutants (HAPs) over a populated city due to accidental release. Ulsan, as one of the megacities in Korea, is chosen as an ideal testbed for the simulation, as it is located in complex terrain and hosts a national industrial complex on the outskirts of the city. The system is based on the California puff model (CALPUFF) for simulating a HAP’s dispersion, in which the three-dimensional atmospheric circulation derived from the observed weather station data is specified at a fine horizontal resolution of 200 m. A test scenario is developed for the accidental release of benzene during the daytime and nighttime, respectively, by a fictitious explosion of a storage container, and the injection amount is determined arbitrarily yet comparable to those in the past accidents. In attempting a quantitative assessment and zoning the level of potential risk over the impacted area, multiple simulations have been conducted each day with different hourly varying meteorological conditions in August. The dispersion characteristics of the air pollutant depend largely on the local wind patterns that vary substantially from day to day. Nevertheless, the composite analysis sufficiently identifies the impacted area by the HAP’s dispersion due to the local prevailing wind such as the land–sea breeze circulation. An immediate hazardous area is determined based on the vulnerability map constructed by zoning the level of risk determined by the spatial distribution of the HAPs’ concentration and the harmfulness standard to the human body.

Opposite interdecadal variations of wintertime haze occurrence over North China Plain and Yangtze River Delta regions in 1980–2013

In this study the interdecadal variations of haze pollution during recent 34 years from 1980 to 2013 over eastern China are investigated. It is found that opposite interdecadal variations of wintertime haze days (WHDs) between the North China Plain region (NCP) and the Yangtze River Delta region (YRD) occurred in this period, i.e., a decreased interdecadal trend of anomalous WHDs appeared in NCP and an increased trend in YRD. Meteorological factors driven the opposite interdecadal variations of anomalous WHDs are revealed. In the phase of interdecadal variations with more WHDs in NCP and less in YRD before 1996, there were weaker northerly winds in the lower troposphere over eastern China accompanied with a weakened Siberia High and mid-latitude westerly jet. The decreased northerly winds are conductive to the local accumulation of air pollutants in NCP and inhibition of air pollutants to be transported from North China to YRD. Consequently, more WHDs appeared in YRD and less in NCP. On the contrary, in the phase of interdecadal variations with less WHDs in NCP and more in YRD after 1996, stronger northerly winds associated with strengthened Siberia High and westerly jet, appeared over eastern China. The increased northerly winds are favorable for the dispersion of air pollutants in NCP and transport more pollutants from North China to the downstream area in YRD, resulting in less WHDs in NCP and more in YRD.

Modeling the salt-dust aerosols distribution in the atmosphere, taking into account the soil erosion

In the general case, when modelling the process of air pollution dispersion, it is necessary to take into account factors associated with the interaction of air mass with the underlying earth surface or wind erosion. The main purpose of this work is to study the factors affecting the amount of particulates carried upward from the soil into the air due to wind erosion. The study of this aspect is very relevant for the analysis of environmental situation in the Aral region of Uzbekistan. The major share of harmful substances emission in Aral Sea region is undertaken by dust, salts and toxic chemicals blown up from dried bottom of the Aral Sea. Thus, in mathematical modelling of atmospheric dispersion process, it is necessary to take into account the physic and mechanical properties of the particles and basic forces acting on them. In the paper there are presented certain numerical calculations for studying the process of soil erosion depending on the air mass velocity of the atmosphere, the size and density of particles, and the acting forces. The basic forces that play a significant role in the process of soil erosion were determined by carried numerical calculations.

Quantification methods of forest and land fires impact on the atmospheric environment (case study: oil palm plantation in Kayuagung District, OKI Regency, South Sumatra)

The impact of forest and land fires on the atmospheric environment can be classified into three components, namely ambient air quality, its contribution to greenhouse gases, and microclimate change. Each component has a different method for assessing and measuring the magnitude of its impact. The aim of the study is to obtain quantitative methods to assess the magnitude of the impact of forest and land fires on the atmospheric environment so that they can be used for the valuation of environmental losses. The magnitude of the impact of the air quality component is measured based on the Air Pollution Index (ISPU) and visibility, the component of the greenhouse gas is assessed by approaching the amount of GHG emissions and / or loss of carbon stocks, while changes in the microclimate by assessing changes in the level of thermal comfort. Gas and particulate emissions values of forest and land fires use the carbon mass balance approach and emission factors. Analysis of air pollution dispersion is conducted use the Gaussian model, with case study is the incidence of land fires in oil palm plantations located in Kayuagung sub-district, Ogan Komering Ilir Regency, South Sumatra Province in 2015, 2016 and 2017. The data used in this study consisted of Landsat 8 satellite imagery, MODIS and VIIRS Hotspots, measurements of vegetation biomass in the field, organic C-peat and climate data during fires. The results of the assessment show that land fires covering 551 ha in 2015, 59 ha in 2016 and 253 ha in 2018 have resulted in changes in the air pollutant standard index in Kayuagung from the medium category (ISPU PM10 = 75) to very unhealthy (ISPU PM10 = 272) in 2015, unhealthy (ISPU CO = 116) in 2016 and very unhealthy (ISPU CO = 205) in 2018. Visibility in an area of about 500-600 meters in the direction of the wind from the fire’s location was less than 1 km with PM10 of more than 176 µg m−3. The contribution of GHGs to each fire’s year is 26.8, 2.8 and 12.3 kilo tons of CO2e consist of CO2 and CH4. The results of this study can be used to quantify the magnitude of the land fires impact on the atmospheric environment.

Haze pollution under a high atmospheric oxidization capacity in summer in Beijing: insights into formation mechanism of atmospheric physicochemical processes

Abstract. Under a high atmospheric oxidization capacity, the synergistic effect of the physicochemical processes in the atmospheric boundary layer (ABL) caused summer haze pollution in Beijing. The southern and southwestern areas, generally 60–300 km away from Beijing, were seriously polluted in contrast to Beijing, which remained clean. Southerly winds moving faster than 20–30 km h−1 since the early morning primarily caused haze pollution initiation. The PM2.5 (particulate matter with a dynamic equivalent diameter smaller than 2.5 µm) level increased to 75 µg m−3 over several hours during the daytime, which was simultaneously affected by the ABL structure. Additionally, the O3 concentration was quite high during the daytime (250 µg m−3), corresponding to a high atmospheric oxidation capacity. Much sulfate and nitrate were produced through active atmospheric chemical processes, with sulfur oxidation ratios (SORs) up to ∼0.76 and nitrogen oxidation ratios (NORs) increasing from 0.09 to 0.26, which further facilitated particulate matter (PM) level enhancement. However, the increase in sulfate was mainly linked to southerly transport. At midnight, the PM2.5 concentration sharply increased from 75 to 150 µg m−3 over 4 h and remained at its highest level until the next morning. Under an extremely stable ABL structure, secondary aerosol formation dominated by nitrate was quite intense, driving the haze pollution outbreak. The PM levels in the southern and southeastern areas of Beijing were significantly lower than those in Beijing at this time, even below air quality standards; thus, the contribution of pollution transport had almost disappeared. With the formation of a nocturnal stable boundary layer (NSBL) at an altitude ranging from 0–0.3 km, the extremely low turbulence kinetic energy (TKE) ranging from 0 to 0.05 m2 s−2 inhibited the spread of particles and moisture, ultimately resulting in elevated near-surface PM2.5 and relative humidity (∼90 %) levels. Due to the very high humidity and ambient oxidization capacity, NOR rapidly increased from 0.26 to 0.60, and heterogeneous hydrolysis reactions at the moist particle surface were very notable. The nitrate concentration steeply increased from 11.6 to 57.8 µg m−3, while the sulfate and organics concentrations slightly increased by 6.1 and 3.1 µg m−3, respectively. With clean and strong winds passing through Beijing, the stable ABL dissipated with the potential temperature gradient becoming negative and the ABL height (ABLH) increasing to ∼2.5 km. The high turbulence activity with a TKE ranging from 3 to 5 m2 s−2 notably promoted pollution diffusion. The self-cleaning capacity of the atmosphere is commonly responsible for air pollution dispersion. However, reducing the atmospheric oxidization capacity, through strengthening collaborative control of nitrogen oxide (NOx) and volatile organic compounds (VOCs), as well as continuously deepening regional joint air pollution control, is urgent.