Severe Air Pollution Episodes Research Articles

Hotspot driven air pollution during crop residue burning season in the Indo-Gangetic Plain, India

Intensive crop residue burning (CRB) in northern India triggers severe air pollution episodes over the Indo-Gangetic Plain (IGP) each year during October and November. We have quantified the contribution of hotspot districts (HSDs) and total CRB to poor air quality over the IGP. Initially, we investigated the spatiotemporal distribution of CRB fire within the domain and pinpointed five HSD in each Punjab and Haryana. Furthermore, we have simulated air quality and quantified the impact of CRB using the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem), incorporating recent anthropogenic emissions (EDGAR v5) and biomass burning emissions (FINN v2.4) inventories, along with MOZART-MOSAIC chemistry. The key finding is that HSDs contributed ∼80% and ∼50% of the total fire counts in Haryana and Punjab, respectively. The model effectively captured observed PM₂.₅ concentrations, with a normalized mean bias (NMB) below 0.2 and R-squared (R2) exceeding 0.65 at the majority of validation sites. However, some discrepancies were observed at a few sites in Delhi, Punjab, Haryana, and West Bengal. The National Capital Region experienced the highest PM₂.₅ concentrations, followed by Punjab, Haryana, Uttar Pradesh, Bihar, and West Bengal. Moreover, HSDs were responsible for about 70% of the total increase in CRB-induced PM₂.₅ in the western, central, and eastern cities, and around 50% in the northern cities. By eliminating CRB emissions across the domain, we could potentially save approximately 18,000 lives annually. Policymakers, scientists, and institutions can leverage the framework to address air pollution at national and global scales by targeting source-specific hotspots. This approach, coupled with appropriate technological and financial solutions, can contribute to achieving climate change and sustainable development goals.

Evaluation of WRF-Chem-simulated meteorology and aerosols over northern India during the severe pollution episode of 2016

Abstract. We use a state-of-the-art regional chemistry transport model (WRF-Chem v4.2.1) to simulate particulate air pollution over northern India during September–November 2016. This period includes a severe air pollution episode marked by exceedingly high levels of hourly PM2.5 (particulate matter having an aerodynamic diameter ≤ 2.5 µm) during 30 October to 7 November, particularly over the wider Indo-Gangetic Plain (IGP). We provide a comprehensive evaluation of simulated seasonal meteorology (nudged by ERA5 reanalysis products) and aerosol chemistry (PM2.5 and its black carbon (BC) component) using a range of ground-based, satellite and reanalysis products, with a focus on the November 2016 haze episode. We find the daily and diurnal features in simulated surface temperature show the best agreement followed by relative humidity, with the largest discrepancies being an overestimate of night-time wind speeds (up to 1.5 m s−1) confirmed by both ground and radiosonde observations. Upper-air meteorology comparisons with radiosonde observations show excellent model skill in reproducing the vertical temperature gradient (r>0.9). We evaluate modelled PM2.5 at 20 observation sites across the IGP including eight in Delhi and compare simulated aerosol optical depth (AOD) with data from four AERONET sites. We also compare our model aerosol results with MERRA-2 reanalysis aerosol fields and MODIS satellite AOD. We find that the model captures many features of the observed aerosol distributions but tends to overestimate PM2.5 during September (by a factor of 2) due to too much dust, and underestimate peak PM2.5 during the severe episode. Delhi experiences some of the highest daily mean PM2.5 concentrations within the study region, with dominant components nitrate (∼25 %), dust (∼25 %), secondary organic aerosols (∼20 %) and ammonium (∼10 %). Modelled PM2.5 and BC spatially correlate well with MERRA-2 products across the whole domain. High AOD at 550nm across the IGP is also well predicted by the model relative to MODIS satellite (r≥0.8) and ground-based AERONET observations (r≥0.7), except during September. Overall, the model realistically captures the seasonal and spatial variations of meteorology and ambient pollution over northern India. However, the observed underestimations in pollutant concentrations likely come from a combination of underestimated emissions, too much night-time dispersion, and some missing or poorly represented aerosol chemistry processes. Nevertheless, we find the model is sufficiently accurate to be a useful tool for exploring the sources and processes that control PM2.5 levels during severe pollution episodes.

The turbulent future brings a breath of fresh air

Ventilation of health hazardous aerosol pollution within the planetary boundary layer (PBL) – the lowest layer of the atmosphere – is dependent upon turbulent mixing, which again is closely linked to the height of the PBL. Here we show that emissions of both CO2 and absorbing aerosols such as black carbon influence the number of severe air pollution episodes through impacts on turbulence and PBL height. While absorbing aerosols cause increased boundary layer stability and reduced turbulence through atmospheric heating, CO2 has the opposite effect over land through surface warming. In future scenarios with increasing CO2 concentrations and reduced aerosol emissions, we find that around 10% of the world’s population currently living in regions with high pollution levels are likely to experience a particularly strong increase in turbulence and PBL height, and thus a reduction in intense pollution events. Our results highlight how these boundary layer processes provide an added positive impact of black carbon mitigation to human health.

Role of urban boundary layer dynamics and ventilation efficiency in a severe air pollution episode in Tehran, Iran

Tehran faces a significant health challenge due to severe air pollution episodes during wintertime, which are associated with high concentrations of fine particulate matter with a diameter less than 2.5 µm (PM2.5). In this study, we investigated meteorology conditions of one of the severe air pollution episodes, occurred from 27th December 2020 to 15th January 2021, using the Weather Research and Forecasting (WRF) model. To gain insights into this episode, we also modeled a clean episode for comparison. Model validation of land surface temperature using remote sensing showed acceptable performance as well as ground observations for other parameters. We then calculated the ventilation coefficient (VC) from the WRF outputs and analyzed the results statistically. Results indicate the severe reduction in both VC and planetary boundary layer height (PBLH) during the polluted episode. We further linked the decrease in PBLH and VC of the polluted episode to a high-pressure system above 1020 hPa. In contrast, the results for the clean episode indicate that the low-pressure system as low as 1010 hPa led to higher PBLH and VC than during the polluted episode. This low-pressure system favors the reduction of PM2.5 levels to lower than 21 μgm−3.

Aerosol mass scattering efficiencies and single scattering albedo under high mass loading in Chiang Mai valley, Thailand

Aerosols amend the Earth's radiation budget by absorbing and scattering the incoming solar radiation. Severe air pollution episodes with high aerosol loading have continually occurred in northern Thailand for a long decade. This study comprehensively investigates the light scattering mechanism contingent on synchronous measurement of aerosol physicochemical and optical properties at Chiang Mai, the second largest city in Thailand per population, for two months during the spring of 2016. Daily mean values of the aerosol light scattering coefficient (σsca) at 550 nm ranged between 146 and 501 Mm−1. The scattering Ångström exponent (SAE450/700) ranged from 1.7 to 2.1, indicating a predominant contribution of finer particles to total light scattering. The mean mass scattering efficiency (MSE) of (NH4)2SO4, NH4NO3, organic matter (OM), dust, and others at 550 nm, estimated using a multilinear regression model were 3.3, 1.4, 4.4, 1.8, and 4.0 m2 g−1, respectively. The mean contribution of individual components to σsca was in the order of OM (66%) > Others (12%) > Dust (11%) > (NH4)2SO4 (9%) > NH4NO3 (2%). The mean (±SD) value of aerosol single scattering albedo at 550 nm wavelength was 0.80 ± 0.02 (range; 0.75–0.84), highlighting the presence of strongly absorbing aerosols. The total light absorption was primarily due to the mixture of organic and elemental carbons. The mean (±SD) MSE and mass absorption efficiency (MAE) of composite aerosols were 3.4 ± 0.4 m2 g−1 and 0.9 ± 0.1 m2 g−1, respectively. Notwithstanding the absorption, a simple radiative transfer model quantifies a negative top-of-atmosphere radiative forcing over Chiang Mai. These findings shed light on the impact of ambient aerosols on light scattering and urban climate. Moreover, our study offers a basic dataset to assess the visibility impairment in Chiang Mai.

Prenatal and early postnatal exposure to air pollution associations with primary care and prescription usage

BACKGROUND AND AIM: Health consequences of air pollution in early life have been mostly studied in hospital settings, with less focus put on primary care and prescribed medications. The aim of this study was to investigate general practitioner (GP) consultations and prescriptions dispensed following exposure in utero and in the first year of life to the Hazelwood coal mine fire, a severe air pollution episode lasting six weeks. METHODS: The Victorian Perinatal Data Collection was linked to the Medicare Benefits Schedule and the Pharmaceutical Benefits Scheme for a cohort of children born in the Latrobe Valley, Australia between March 2012 and December 2015. Modelled estimates of fire-related PM2.5 exposure were assigned at the residential address at birth. The total numbers of GP visits and of prescriptions of antibiotics, asthma inhalers and steroid skin creams dispensed in the first year of life or in the year following the fire were extracted for children exposed in utero and in infancy (<1 year old), respectively. Negative binomial regression models estimated associations between each outcome and exposure to fire-related PM2.5, with adjustment made for potential confounders. RESULTS: Higher levels of PM2.5 in utero were associated with increased asthma inhalers dispensed (IRR=1.07, 95%CI=1.00-1.14 per 100µg/m³ of cumulative PM2.5; IRR=1.27, 95%CI=1.01-1.58 per 50µg/m3 of peak 24-h PM2.5) in infancy. Surprisingly, a cumulative exposure >25 µg/m³ in infancy was linked to fewer GP visits (IRR=0.83, 95%CI=0.68-0.99) in the year following the fire. CONCLUSIONS: Our findings indicate that prenatal exposure to time-limited severe air pollution could be linked with increased need of asthma medications in infancy. They also suggest that such exposure in infancy could be associated with less GP consultations following extreme events, which could be due to increased needs of specialised and hospital care. KEYWORDS: Particulate matter; Long-term exposure; Infections; Asthma

Effectiveness of a Protocol to Reduce Children's Exposure to Particulate Matter and NO2 in Schools during Alert Days.

Reducing children’s exposure to air pollutants should be considered a primary goal, especially for the most vulnerable subjects. The goal of this study was to test the effectiveness of applying a protocol in the event of alert days, i.e., days with forecasted PM10 levels above the EU limit value (50 µg/m3). The test was conducted, before the onset of SARS-CoV-2 restrictions, in a classroom of a primary school in Parma (Italy)—a highly polluted area in Northern Italy. The protocol included indications for the frequency of opening windows and doors, as well as the activation of an air purifier. Teachers and students were asked to apply the protocol only in the event of alert days, while no indications were provided for non-alert days. A monitoring system measuring PM1, PM2.5, PM10, CO2, and NO2 was deployed in the classroom. Measurements of the same parameters were also performed outdoors near the school. The application of the protocol reduced the indoor/outdoor (I/O) ratio for all toxic pollutants. The reduction was also remarkable for PM10—the most critical air quality parameter in the study area (1.5 and 1.1 for non-alert and alert days, respectively). Indoor concentrations of PM10—especially during non-alert days—were often higher than outdoors, showing a major contribution from resuspension due to the movement of people and personal cloud. The protocol did not cause any increase in indoor CO2 levels. Our findings showed that the application of a ventilation protocol together with the contribution of an air purifier may represent an effective way to reduce children’s exposure to air pollution during severe air pollution episodes. Considering the onset of COVID-19 and the airborne transmission of pathogens, this protocol now has more meaningful implications for children’s welfare, and can be integrated with protocols designed as measures against the spread of SARS-CoV-2.

Two Typical Patterns of Regional PM2.5 Transport for Heavy Air Pollution Over Central China: Rapid Transit Transport and Stationary Accumulation Transport

The regional transport of air pollutants has been identified as a critical factor that affects air quality over downwind receptor areas; however, the regional transport patterns for air pollution episodes remain poorly understood. In this study, we identified two distinct patterns of regional transport: rapid transit transport (RTT) and stationary accumulation transport (SAT), both of which induced severe PM2.5 pollution episodes in central China during 2015–2020. The differences and similarities between the two regional transport patterns of air pollution were characterized by their influencing meteorological factors. Similar meteorological conditions trigger the RTT and SAT, with a high-PM2.5 concentration air mass from the upstream regions transported to the Twain-Hu Basin (THB) by the strong northerly winds with a southward advance of cold air mass. The average rate of increase in the PM2.5 concentration of the RTT (12.5 μg/m3/h) is more than that of the SAT (5.7 μg/m3/h). However, meteorological conditions evolved differently in RTT and SAT. For RTT with the fast passage of cold air, the THB is located behind the strong cold front during the later stage, and these events rapidly ended owing to the northerly winds and wet scavenging of precipitation. For SAT with the slow cold air accumulation, the THB is mainly occupied by a weak high-pressure system with low wind speeds, strong descending airflow, and a low atmospheric boundary layer height, trapping the air pollutants accumulated in the THB and resulting in persistent heavy pollution incidents. This study provides new insights into the meteorological mechanism underlying the formation of severe air pollution episodes over a receptor region owing to the regional transport patterns of air pollutants.

Inter-annual variability of ice nucleating particles in Mexico city

The continuous and sustained population shift from rural to urban areas is driving most of the fast-growing megacities on a global scale. Considerable pollution, gases and particulate matter, is emitted yearly into the atmosphere of megacities, with unclear impacts on the local and regional hydrological cycle. The present work evaluated the inter-annual variability of super-micron (1.0–10 μm) ice nucleating particles (INP), via immersion freezing, sampled during the dry-warm season in Mexico City on two consecutive years using the UNAM-MicroOrifice Uniform Deposit Impactor-Droplet Freezing Technique (UNAM-MOUDI-DFT). The aerosol particles emitted in Mexico City were found to act as INP via the immersion freezing mode at temperatures below −20 °C with INP concentrations ranging between 0.74 L-1 (−20 °C) and 20.42 L-1 (−30 °C). Although the INP concentration varied between the dry-warm seasons, the average concentrations between 2018 and 2019 were rather similar, with significant differences only observed at −20 °C. The large increase (>200%) in fine particulate matter -PM2.5- observed during the 2019 severe air pollution episode caused by biomass burning (BB) emissions, did not impact the super-micron INP concentrations between −20 °C and −30 °C. However, INPs at temperatures above −15 °C were found to increase during the severe pollution episode. Given that such warm ice nucleation temperatures can be linked with the presence of biological particles, the present observations suggest that the BB plumes transported into Mexico City were most likely advecting co-emitted biological particles.

A Movable Fog-Haze Boundary Layer Conceptual Model Over Jianghuai Area, China

The Jianghuai area is an “important” region not only for its local pollutant accumulation but the belt for pollutant transportation between North China and the Yangtze River Delta during the winter half of the year (often from October to next February). In this study, a movable boundary layer conceptual model for the Jianghuai area in the winter half of the year is established based on the analyses of characteristics of atmospheric circulations and boundary layer dynamic conditions. This conceptual model can well explain the causes of air quality change and frequent fog-haze episodes. Variations of the intensity and range of the cold and warm fronts in the Jianghuai area in the winter half of the year lead to form a movable boundary in this area. When the southerly wind is strong, or affected by strong cold air mass, the air quality in the Jianghuai area may be excellent with a low air pollution index; Two atmospheric circulations provide favorable conditions for the fog-haze formation and maintenance in Jianghuai area: 1) When the shallow weak cold air mass is below the deep moist warm air mass, a stable temperature inversion occurs. The pollutants are transported to the Jianghuai area by the weak cold air mass, and local emissions also accumulate. As a result, a severe air pollution episode appears. 2) When the northerly cold air mass is as intense as the southerly moist warm air mass, the pollutants transported from North China as well as local emissions will continuously accumulate in the study area, which may lead to more severe air pollution. This conceptual model can help us analyze atmospheric diffusion capacity, and benefit the forecast and early warning of airflow stagnation area and fog-haze episode.

The Occurrence of Heavy Air Pollution during the COVID-19 Outbreak in Beijing, China: Roles of Emission Reduction, Meteorological Conditions, and Regional Transport

To prevent the spread of coronavirus disease (COVID-19) and mitigate the epidemic risk, strict lockdown measures were implemented in Beijing during the quarantine period, significantly reducing human activities. However, severe air pollution episodes occurred frequently in Beijing. To explore the occurrence of severe air pollution during the quarantine period, the impacts of emission reductions, meteorological conditions, and regional transport on heavy air pollution were individually evaluated using the Community Multiscale Air Quality (CMAQ) model. Observations showed that the more unfavorable meteorological conditions which occurred during the pandemic as compared to the corresponding 2019 levels, including higher temperature, relative humidity, and frequency of strong southerly winds, and lower HPBL, led to an increase in PM2.5 concentrations. The model results also showed that the meteorological conditions in February 2020 favored PM2.5 formation. The PM2.5 concentrations were mainly dominated by regional transport, which became more significant in the quarantine period than in 2019, suggesting the importance of joint control on regional sources for reducing heavy air pollution. This study highlights that, although the emissions in Beijing and surrounding regions were largely reduced during the quarantine period, severe air pollution in Beijing did not reduce due to the unfavorable meteorological conditions.

The state of science on severe air pollution episodes: Quantitative and qualitative analysis.

Severe episodic air pollution blankets entire cities and regions and have a profound impact on humans and their activities. We compiled daily fine particle (PM2.5) data from 100 cities in five continents, investigated the trends of number, frequency, and duration of pollution episodes, and compared these with the baseline trend in air pollution. We showed that the factors contributing to these events are complex; however, long-term measures to abate emissions from all anthropogenic sources at all times is also the most efficient way to reduce the occurrence of severe air pollution events. In the short term, accurate forecasting systems of such events based on the meteorological conditions favouring their occurrence, together with effective emergency mitigation of anthropogenic sources, may lessen their magnitude and/or duration. However, there is no clear way of preventing events caused by natural sources affected by climate change, such as wildfires and desert dust outbreaks.

The Wasatch Environmental Observatory: A mountain to urban research network in the semi‐arid westernUS

AbstractThe 2085 km2Jordan River Basin, and its seven sub‐catchments draining the Central Wasatch Range immediately east of Salt Lake City, UT, are home to an array of hydrologic, atmospheric, climatic and chemical research infrastructure that collectively forms the Wasatch Environmental Observatory (WEO). WEO is geographically nested within a wildland to urban land‐use gradient and built upon a strong foundation of over a century of discharge and climate records. A 2200 m gradient in elevation results in variable precipitation, temperature and vegetation patterns. Soil and subsurface structure reflect systematic variation in geology from granitic, intrusive to mixed sedimentary clastic across headwater catchments, all draining to the alluvial or colluvial sediments of the former Lake Bonneville. Winter snowfall and spring snowmelt control annual hydroclimate, rapid population growth dominates geographic change in lower elevations and urban gas and particle emissions contribute to episodes of severe air pollution in this closed‐basin. Long‐term hydroclimate observations across this diverse landscape provide the foundation for an expanding network of infrastructure in both montane and urban landscapes. Current infrastructure supports both basic and applied research in atmospheric chemistry, biogeochemistry, climate, ecology, hydrology, meteorology, resource management and urban redesign that is augmented through strong partnerships with cooperating agencies. These features allow WEO to serve as a unique natural laboratory for addressing research questions facing seasonally snow‐covered, semi‐arid regions in a rapidly changing world and an excellent facility for providing student education and research training.

Real-time quantification and source apportionment of fine particulate matter including organics and elements in Delhi during summertime

Delhi is one of the most polluted cities globally, with frequent severe air pollution episodes and haze events occurring in recent years, thereby compelling us to understand the sources to develop effective mitigation plans. Complete chemical characterization of fine particulate matter (PM2.5) components (non-refractory, refractory and elements) with high time resolution has been done during the summer season (June–July 2019). The total PM equivalent (PM2.5(eq)) was 28.7 ± 13.2 μg m−3 of which elements dominated the PM2.5(eq) with 34% contribution followed by organics (28%), black carbon (BC) (17%), SO42− (10%), Cl− (5%) NH4+ (3.5%) and NO3− (2.5%). The contributions from organic aerosols (OA) and SO42− were observed to be more than Cl− and NO3−. The total elemental mass concentration (PMEl) was mostly contributed (~96%) by Si, S, Cl, Ca, K, Fe and Al with Si and S alone contributing around 50% of PMEl. Crustal elements (Al, Fe, Ca and Si) were highly enhanced in summer than elements emitted from anthropogenic emissions (Cl, S, K, Pb and Zn). Source apportionment (SA) of PM was performed using positive matrix factorization (PMF) together with ME-2 (multilinear engine) for OA and elements, separately. PMF on both datasets helped resolve sources such as combustion, industrial, dust-related, incineration and traffic. OA PMF identified three factors related to primary emissions: hydrocarbon-like OA (HOA, 12.3%), solid fuel combustion (SFC, 16.2%) and cooking OA (COA, 7.3%) and two oxygenated OA (OOA): semi-volatile OOA (SVOOA, 15.2%) and low-volatile OOA (LVOOA, 49.1%). The elemental PMF resolved 8 factors: dust (52.5%), S-rich (16.2%), Cl-rich (10.7%), 2 SFC factors (10.5%), non-exhaust (7.2%), Cu-rich (1.5%) and industrial (1.4%). The contribution of BC to total PM mass is shown to increase in the summer compared to previous studies reported for the winter season. The secondary oxidized sources dominated both the OA and elements SA during the summer with 64.3% and 27% (dust not considered) contribution, respectively. The domination of secondary sources implies that it is crucial to control the secondary aerosols' precursors in Delhi for developing pollution control strategies. The ME-2 resolved factors, coupled with concentration weighted trajectory (CWT) showed the probable major elemental source regions of local origin (Delhi- National Capital Region (Delhi-NCR)) as well as regional (from Punjab, Haryana, Uttar Pradesh and Pakistan). The local sources included Cu-rich (Haryana) and SFC-II (Delhi and Uttar Pradesh), while the regional sources were dust (south-west (SW)), industrial, Cl-rich (north-west (NW)), SFC-I (east and south-east (SE)) and S-rich (SE).

Key factors explaining severe air pollution episodes in Hanoi during 2019 winter season

With the aim of identifying key factors explaining the severe pollution events that occur under the impact of the Northeast monsoon during the winter period in Hanoi, a two-month campaign was carried out (11 January to 22 March 2019). The local meteorological parameters and the origin of the air masses were investigated, notably using a Doppler Lidar, and the structure of the boundary layer was thoroughly studied using elastic Lidar measurements for the first time in Hanoi. Four heavily polluted events occurred during the campaign, which were associated with hazy days; the highest daily PM2.5 concentrations reached ~130 μg m−3 while the mean concentration during the campaign was 45 ± 25 μg m−3. These severe polluted events in Hanoi were mainly related to LRT coming from China besides local emission or LRT from other polluted regions of Vietnam. BLH proved to be one of the key factors controlling air pollution in Hanoi. Indeed, the elastic Lidar measurements showed that the daily maximum of the hourly BLH varied from 700m to 1200m during cloudy days, while it was always below 1000m during hazy days. The lower BLH on the hazy days weakened the vertical mixing and was directly related to an increase in aerosol concentrations at the surface.

Another one breathes the dust. The relation between severe air pollution episodes and school attendance in southern Chile

ABSTRACT The intermediate-sized cities of southern Chile experience days of high pollution levels every winter due to the use of wood-burning stoves. Several studies have analysed the factors that hinder energy transition and the social acceptance of measures to improve air quality, the consequences of which are disturbing. However, they have mainly focused on health issues without considering the social impacts of air pollution. This study aims to assess whether exposure to outdoor air pollution is associated with school absenteeism. We analysed the records of approx. 5,000 students in the fourth grade from 25 schools in five cities in southern Chile (2010–2017). Using a fixed-effects model and applying it to the school level, we were able to estimate the effect of air pollution on absenteeism from school after controlling for the effects of individual characteristics. Previous studies have found that independent of air pollution, students from low-income families have a higher absenteeism rate. Our findings suggest that as air pollution worsens, pupils from middle and high-income households are also more likely to miss school days. We argue that this is, presumably, because high-income families are able to develop protective behaviour such as bringing their children to the doctor or keeping them at home on highly polluted days.

Effects of AIR pollution on cardiopuLmonary disEaSe in urban and peri-urban reSidents in Beijing: protocol for the AIRLESS study

Abstract. Beijing, as a representative megacity in China, is experiencing some of the most severe air pollution episodes in the world, and its fast urbanization has led to substantial urban and peri-urban disparities in both health status and air quality. Uncertainties remain regarding the possible causal links between individual air pollutants and health outcomes, with spatial comparative investigations of these links lacking, particularly in developing megacities. In light of this challenge, Effects of AIR pollution on cardiopuLmonary disEaSe in urban and peri-urban reSidents in Beijing (AIRLESS) was initiated, with the aim of addressing the complex issue of relating multi-pollutant exposure to cardiopulmonary outcomes. This paper presents the novel methodological framework employed in the project, namely (1) the deployment of two panel studies from established cohorts in urban and peri-urban Beijing, with different exposure settings regarding pollution levels and diverse sources; (2) the collection of detailed measurements and biomarkers of participants from a nested case (hypertensive) and control (healthy) study setting; (3) the assessment of indoor and personal exposure to multiple gaseous pollutants and particulate matter at unprecedented spatial and temporal resolution with validated novel sensor technologies; (4) the assessment of ambient air pollution levels in a large-scale field campaign, particularly the chemical composition of particulate matter. Preliminary results showed that there is a large difference between ambient and personal air pollution levels, and the differences varied between seasons and locations. These large differences were reflected on the different health responses between the two panels.

Vertical distribution and transport of air pollutants during a regional haze event in eastern China: A tethered mega-balloon observation study

One vertical observation field campaign based on a tethered mega-balloon (with onboard instruments over 200 kg) was conducted at a campus site in rural Shanghai in order to investigate the vertical distributions of key air pollutants (PM2.5, SO2, black carbon (BC) and O3) and regional transport characteristics during a severe air pollution episode in mid-December 2015. Vertical patterns of measured air pollutants show relatively even profiles within the planetary boundary layer (PBL) while declined sharply above PBL during the daytime. Specifically, high concentrations of SO2 were observed near the top of the boundary layer. Lagrangian particle dispersion modeling showed air pollutants within the boundary layer mainly derived from local sources (i.e. Shanghai) and regional transport within the Yangtze River Delta (YRD) region in the morning before the development of boundary layer.Aerosol chemical components measured at a ground site (about 60 km northwest of the balloon site) showed that regional transport brought a large amount of aged sulfate and nitrate. This study provides new insights in the vertical distribution and transport of haze associated with the PBL development and long-range transport.

Abnormally Shallow Boundary Layer Associated With Severe Air Pollution During the COVID-19 Lockdown in China.

After the 2020 Lunar New Year, the Chinese government implemented a strict nationwide lockdown to inhibit the spread of the Coronavirus Disease 2019 (COVID‐19). Despite the abrupt decreases in gaseous emissions caused by record‐low anthropogenic activities, severe haze pollution occurred in northern China during the COVID lockdown. This paradox has attracted the attention of both the public and the scientific community. By analyzing comprehensive measurements of air pollutants, planetary boundary layer (PBL) height, and surface meteorology, we show that the severe air pollution episode over northern China coincided with the abnormally low PBL height, which had reduced by 45%, triggering strong aerosol‐PBL interactions. After dynamical processes initiated the temperature inversion, the Beijing metropolitan area experienced a period with continuously shallow PBLs during the lockdown. This unprecedented event provided an experiment showcasing the role of meteorology, in particular aerosol‐PBL interactions in affecting air quality.

Study of Secondary Organic Aerosol Formation from Chlorine Radical-Initiated Oxidation of Volatile Organic Compounds in a Polluted Atmosphere Using a 3D Chemical Transport Model.

The impact of chlorine (Cl) chemistry on the formation of secondary organic aerosol (SOA) during a severe wintertime air pollution episode is investigated in this study. The Community Multiscale Air Quality (CMAQ) model v5.0.1 with a modified SAPRC-11 gas-phase mechanism and heterogeneous reactions for reactive chlorine species is updated to include the formation of chlorine radical (Cl•)-initiated SOA (Cl-SOA) from aromatic compounds, terpenes, and isoprene. Reported SOA yield data on Cl-SOA formation from environmental chamber studies are used to derive the mass yield and volatility data for the two-product equilibrium-partitioning model. The heterogeneous reaction of particulate chloride (pCl-) leads to a significant increase in the Cl• and hydroxyl radical (OH) concentrations throughout the domain. Monthly Cl-SOA concentrations range from 0.7 to 3.0 μg m-3, with increasing anthropogenic Cl emissions leading to higher Cl-SOA concentrations. Indirectly, this also leads to an increase of monthly SOA by up to 2.5-3.0 g μm-3 from the traditional OH oxidation pathways as well as the surface uptake of glyoxal and methylglyoxal. Increased OH concentrations, however, do not always lead to higher overall SOA concentrations in the entire domain. High OH reduces the lifetime of glyoxal/methylglyoxal (GLY/MGLY), making them less available to form SOA. In the Sichuan Basin (SCB) and part of Southwest China where high O3 concentrations meet high pCl emissions, a higher Cl•/OH ratio leads to net O3 loss from the Cl• + O3 reaction, thus reducing SOA formation from the O3 oxidation of volatile organic compounds (VOCs). Also, the competition between Cl• and OH for VOCs could lead to lower overall SOA because the molar yields of the semivolatile products in Cl-VOC reactions are lower than their OH + VOC reaction counterparts. When Cl• concentrations are further increased with higher emissions of Cl, precursor gases can be depleted and become the limiting factor in SOA formation. This study reveals the direct and indirect impacts of chlorine chemistry on SOA in polluted winter conditions, which are greatly affected by the Cl emissions, the ambient O3 level, and the availability of SOA precursors.