Transport Of Atmospheric Pollutants Research Articles

Unveiling the health impacts of air pollution transport in China

The transport of atmospheric pollutants plays a pivotal role in regional air pollution, highlighting critical concerns over the unequal health outcomes that arise from such transport. While previous researches predominantly focused on key areas in the battle against air pollution, the intensification of control measures necessitates a national perspective to comprehend the health impacts due to pollution transport. Our study establishes an integrated assessment framework that combine an emission-concentration response surface model with a health impact evaluation model to analyse the nationwide health impacts of PM2.5 and O3 pollution transport across China’s 31 provinces. We found that, interprovincial transport of PM2.5 and O3 contributed to 747,000 and 110,000 deaths respectively in 2017, which amounts to 38% and 48% of deaths caused by total anthropogenic emissions. North, East, and Central China together contribute 82% and 69% to the health impacts caused by regional PM2.5 and O3 transport respectively, and the transport among these three regions is also significant. The analysis of interprovincial health impact transport shows that, for PM2.5, the top contributors are Hebei, Shandong, Henan, Anhui, and Jiangsu, with the most affected being Henan, Shandong, Jiangsu, Hebei, and Guangdong. Regarding O3, Shandong, Hebei, Henan, Jiangsu, and Anhui contribute the most, while Henan, Shandong, Hebei, Jiangsu, and Anhui are the most affected. This study can shed lights on regional control strategies by prioritizing control areas based on the health impact of air pollution transport in China.

Chasing parts in quadrillion: applications of dynamical downscaling in atmospheric pollutant transport modelling during field campaigns

Atmospheric transport and dispersion models (ATDMs) are widely used to study and forecast pollution events. In the frame of the “Effect of Megacities on the transport and transformation of pollutants on the regional to global scales” (EMeRGe) project, ATDM forecasts were carried out to identify potential airborne sampling areas of perfluorocarbons (PFCs) emanating from controlled PFC releases. The forecasts involved short-distance transport over small-scale topographic maxima (Manilla; Philippines), short-distance transport over large-scale topographic maxima (Taipei, Taiwan) and long-distance transport over mixed topography (Nanjing, China, sampled over Taiwan). In situ aircraft measurements of PFC mixing ratios down to a few parts per quadrillion (ppqv) provide us with a unique dataset to explore the added benefits of dynamical downscaling. Transport simulations were repeated using FLEXPART driven by ERA5 and IFS meteorological data and FLEXPART-WRF with dynamically downscaled IFS data down to 1.1 km and four PBL parametrisations. Of the three cases studied, dynamical downscaling led to significant differences for the Manilla and Taipei releases that can be interpreted through changes in the modelled orographic flow regimes. The choice of PBL scheme also significantly impacted accuracy, but there was no systematically better-performing option, highlighting the benefits of ensemble forecasting. Results show how convergence and divergence between ensemble members can be utilised to help decision-making during field campaigns. This study highlights the role that dynamical downscaling can play as an important component in campaign planning when dealing with observations over orographically complex areas.

Analysis of atmospheric pollutant characteristics and regional transport in coastal area along the East China Sea

PM2.5 and black carbon (BC) are important air pollutants impacting radiation balance, air quality, health, and ecosystems. Ozone (O3) levels are increasing despite decreases in other pollutants, posing a challenge for pollution control, especially in coastal cities like Zhoushan, where the monsoonal climate can exacerbate PM2.5 and ozone pollution. This study conducted continuous online measurements of major atmospheric pollutants in Zhoushan, Zhejiang Province, in 2020. The results indicate that the highest contribution from local air masses in Zhoushan is observed in spring, accounting for 17.7 %, while the greatest average contribution from northern Zhejiang Province, Jiangsu Province, and Shanghai occurs in winter, at 18.5 %. Pollutant concentrations were seasonally variable, with PM2.5, BC, and sulfur dioxide concentrations 56.6 %, 36 %, and 58.2 % higher in the cold season compared to the warm season. The O3 in spring is approximately 50 % higher than that in summer. Ship emissions significantly contributed to BC, nitrogen oxides (NOx), and carbon monoxide in Zhoushan. In spring, PM2.5 sources included photochemical processes and northern air mass transport, while in winter, PM2.5 was due to regional transport. The inhibitory effect of PM2.5 on O3 formation in the Zhoushan area is relatively weak. Reducing NOx emissions may increase O3, emphasizing the need for volatile organic compounds monitoring and regional control measures to improve air quality and ensure sustainable development in Zhoushan.

Uncovering sources, distribution, and seasonal patterns of trace element deposition: the elemental puzzle of the western Himalayas.

The transport and deposition of atmospheric pollutants in the Himalayas have a adverse impact on the climate, cryosphere, ecosystem, and monsoon patterns. Unfortunately, there is a insufficiency of data on trace element concentrations and behaviors in the high-altitude Himalayan region, leading to limited research in this area. This study presents a comprehensive and detailed comprehension of trace element deposition, its spatial distribution, seasonal variations, and anthropogenic signals in the high-altitude Kashmir region of the Western Himalayas. Our investigation involved the analysis of 10 trace elements (Al, Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd, and Pb) in glacier ice, snow pits, surface snow, and rainwater collected at various sites including Kolahoi, Thajwas, Pahalgam (Greater Himalayan ranges), and Kongdori and Shopian (Pir Panjal Ranges) during 2021.The study reveals distinct ranges of concentrations for the trace elements at different sampling sites. Our analysis of trace element concentration depth profiles in snow pits reveals seasonal fluctuations during the deposition year. The highest concentrations were found in the autumn(below 20cm) and summer (top layer), compared to the winter concentration (10-20cm). The high enrichment factors (EFs) suggest the severity of human-induced trace metal deposition in the western Himalayan region, relative to surrounding regions. Surprisingly, the concentrations and EFs of trace elements showed seasonal contradictions, with lower concentration values and higher EFs during the non-monsoon season and vice versa. A source apportionment analysis using the positive matrix factorization (PMF) technique identified five sources of trace element deposition in the region, including crustal sources (32.33%), coal combustion (15.62%), biomass burning (17.63%), traffic emission (18.8%), and industrial sources (15.6%). Additionally, the study incorporated backward trajectories coupled with δ18O using the NOAA HYSPLIT model to estimate moisture sources in the region, which suggests atmospheric pollutants predominately deposited from the large-scale atmospheric circulation from westerlies (75%) during non-monsoon season. These findings underscore the urgent need for enhanced monitoring and research efforts in the future.

Distribution Characteristics of Near Surface Ozone Volume Fraction in Shanxi Province Based on Atmospheric Composition Observation Network

Based on the continuous data of O3， NO， NO2， and NOx and the meteorological data from March 2019 to February 2020 at six atmospheric composition observation stations in Shanxi Province， the characteristics and influence factors of O3 volume fractions were studied using statistical analysis and backward trajectory analysis. The results showed that O3 volume fractions were generally higher from April to September and lower from October to the following March. During the study period， O3 pollution represented by φ（MDA8O3）， i.e.， the maximum daily 8-h average of O3 volume fractions， was the most serious at the Jincheng and Linfen stations in the south of Shanxi， followed by that in the Wutaishan， Shuozhou， and Datong stations in the north， with the least pollution occurring at the Taiyuan station in the middle. There were differences between the urban and alpine stations， although their seasonal O3 volume fractions were both summer > spring > autumn > winter. O3 volume fractions at the urban station were usually lower than those at the alpine station； O3 at the urban station might have been influenced by photochemical reactions with precursor NOx； however， this was not the main source of high O3 at the alpine station. The peak and valley values appeared at 15：00 and 06：00， respectively， at the urban station， whereas they appeared at 20：00 and 10：00， respectively， at the alpine station， representing diametrically opposite diurnal variation patterns. Further， the daily amplitude of O3 at the urban station was much larger than that at the alpine station. For urban stations specifically， temperature was the most important meteorological factor affecting O3 volume fraction， compared with sunlight hours， precipitation， and total cloud cover. The NO2 volume fraction in the daytime affected the daily amplitude of O3； although the photochemical generation potential of O3 at the Taiyuan station was good， the O3 volume fractions were the lowest among urban stations due to strong NO titration. The higher O3 corresponded to lower NOx in which NO2 was dominant， and the higher NOx was largely composed of NO， under which conditions O3 would be depleted completely. The surface wind that affected O3 volume fractions of all stations primarily came from the southeast， south， and southwest， and specific wind speed led to the increase in O3 volume fraction. The geographical situation of the station would cause the difference in the transport of atmospheric pollutants， whereas the horizontal transmissions of high O3 from the North China Plain and Fenwei Plain were likely to be the common reason for the increase in O3 volume fraction in Shanxi.

Measurement of the vertical distributions of atmospheric pollutants using an uncrewed aerial vehicle platform in Xi'an, China.

Vertical observations of atmospheric pollutants play crucial roles in a comprehensive understanding of the distribution characteristics and transport of atmospheric pollutants. A hexacopter uncrewed aerial vehicle equipped with miniature monitors was employed to measure the vertical distribution of atmospheric pollutants within a height of 1000 m at a rural site in Xi'an, China, in 2021. The concentrations of carbon monoxide (CO) and particulate matter (PM) showed generally decreasing trends with increasing height. The ozone (O3) concentration showed a general increasing trend with height followed by a gradual decreasing trend. Vertical decrements of PM2.5 and CO from 0 to 1000 m were significantly (p < 0.05) lower on observation days during summer (14.0 ± 8.1 μg m-3 and 8.7 ± 6.6 ppb, respectively), compared with those in winter (78.3 ± 14.1 μg m-3 and 34.8 ± 17.3 ppb, respectively). The horizontal transport of PM and CO mostly occurred in the morning and at night during winter observations at an altitude of 400-500 m. During the winter haze, the PM and CO profile concentrations below 500 m increased substantially with the decrease in the height of the thermal inversion layer. Vertical O3 transportation was observed in the afternoon and evening during summer, and a ∼37.7% (11.6 ppb) increase in ground-level O3 was observed in relation to vertical transport from the upper atmosphere. The results provide insights into the vertical distribution and transport of atmospheric pollutants in rural areas near cities.

The influence of meteorological parameters on PM2.5 and PM10 values in Ümraniye and Silivri districts of İstanbul

In this study, spatiotemporal relationship between PM2.5 and PM10 concentrations and meteorological parameters were investigated for Silivri and Umraniye districts in Istanbul for 2014-2020. For this purpose, hourly PM2.5 and PM10 concentrations values of two air quality monitoring stations and meteorological data (wind speed, wind direction, relative humidity, total precipitation, minimum and maximum temperature) were examined. In all seasons, while PM concentrations were lowest at 06:00 local time (LT), PM2.5 and PM10 have peak values around 09:00 and 19:00 LT both in Silivri and Umraniye mainly due to anthropogenic activities such as vehicle exhaust emissions. In daily perspective, highest PM values were observed on Sundays in winter at Silivri. On the other side, peak PM values are shown on Fridays at Umraniye. It was found that local emission sources during low wind speeds cause the highest PM2.5 concentrations during winter months and southerly winds exceeding 8 m/s increase the PM10 levels at Silivri and Umraniye. The statistical analysis showed that PM2.5 and PM10 concentrations at Silivri were negatively correlated with wind speed with correlation coefficients of -0.56 (winter), -0.47 (autumn), respectively. Wind speed is negatively associated with PM2.5 (r=-0.48) and PM10 (r=-0.38) in winter season at Umraniye. In addition to this, relative humidity showed negative relationship with PM10 (r=-0.43) in spring at Silivri, while a positive correlation was found between PM10 (r=0.40) and PM2.5 (r=0.38) measured in the summer season and the maximum temperature. In addition to the anthropogenic factors (e.g. urbanization, transportation, and industrialization) that decrease air quality of Istanbul, local meteorological variables and atmospheric transport of pollution are observed to be the other factors that contribute to air pollution.

Impact of the Guinea coast upwelling on atmospheric dynamics, precipitation and pollutant transport over southern West Africa

Abstract. In West Africa, the zonal band of precipitation is generally located around the southern coast in June before migrating northward towards the Sahel in late June/early July. This gives way to a relative dry season for coastal regions from Côte d'Ivoire to Benin called “little dry season”, which lasts until September–October. Previous studies have noted that the coastal rainfall cessation in early July seems to coincide with the emergence of an upwelling along the Guinea coast. The aim of this study is to investigate the mechanisms by which this upwelling impacts precipitation, using a set of numerical simulations performed with the Weather Research and Forecasting regional atmospheric model (WRF v 3.7.1). Sensitivity experiments highlight the response of the atmospheric circulation to an intensification or reduction of the strength of the coastal upwelling. They clearly show that the coastal upwelling emergence is responsible for the cessation of coastal precipitation by weakening the northward humidity transport, thus decreasing the coastal convergence of the humidity transport and inhibiting the deep atmospheric convection. In addition, the diurnal cycle of the low-level circulation plays a critical role: the land breeze controls the seaward convergence of diurnal anomaly of humidity transport, explaining the late night–early morning peak observed in coastal precipitation. The emergence of the coastal upwelling strongly attenuates this peak because of a reduced land–sea temperature gradient in the night and a weaker land breeze. The impact on the inland transport of anthropogenic pollution is also shown with numerical simulations of aerosols using the CHIMERE chemistry-transport model: warmer (colder) sea surface temperature (SST) increases (decreases) the inland transport of pollutants, especially during the night, suggesting an influence of the upwelling intensity on the coastal low-level jet. The mechanisms described have important consequences for inland humidity transport and the predictability of the West African monsoon precipitation in summer.

Source Attribution and Process Analysis of Summertime Ozone Pollution in Guanzhong Basin, Northwestern China

The adverse effects of the transportation of O3 and its precursors on local air quality under certain meteorological conditions has long been recognized. Previous studies covered the effects of their transport without distinguishing specific forms (direct transport, via air pollutants originating from emissions outside the target regions; indirect transport, via air pollutants generated from chemical reactions between local and outside precursors) and processes (chemical and physical). This study aimed to figure out the effects of different scales of emissions on O3 pollution in the Guanzhong basin (GZB) by quantifying the forms and processes of transport using the CAMx model. The results showed that the emissions on different scales had various pathways for influencing O3 formation under two polluted, synoptic circulation types (southeast high and northeast ridge). Under the southeast high type, the meteorological conditions favored the chemical production of O3, which led to the highest local O3 contributions from the GZB. The prominent cross-regional transport was positive for indirect transport from south Shaanxi, implying the synergistic impacts of biogenic VOCs and urban pollutants in the GZB. With the southerly winds in the GZB, the downwind cities of Xi’an were impacted by positive direct and indirect transport from the emissions of Xi’an. These impacts occurred through the processes of gas-phase chemistry (especially O3P + O2 and O3 + NO) and vertical advection. For the northeast ridge type, positive direct transport from the emissions of Henan Province was important for O3 pollution in the GZB, as there were remarkable easterly airflows. From the east to the west of the GZB, the impacts from the emissions from Henan Province on cities in the GZB were reduced, which occurred through the processes of horizontal advection and vertical dispersion. This work highlights significant differences in the forms and processes of O3 formation in downwind areas impacted by the emissions from different-scale emissions, and advances our knowledge of atmospheric pollutant transport and its impact on O3 pollution.

Passive-tracer modelling at super-resolution with Weather Research and Forecasting – Advanced Research WRF (WRF-ARW) to assess mass-balance schemes

Abstract. Super-resolution atmospheric modelling can be used to interpret and optimize environmental observations during top-down emission rate retrieval campaigns (e.g. aircraft-based) by providing complementary data that closely correspond to real-world atmospheric pollution transport and dispersion conditions. For this work, super-resolution model simulations with large-eddy-simulation sub-grid-scale parameterization were developed and implemented using WRF-ARW (Weather Research and Forecasting - Advanced Research WRF). We demonstrate a series of best practices for improved (realistic) modelling of atmospheric pollutant dispersion at super-resolutions. These include careful considerations for grid quality over complex terrain, sub-grid turbulence parameterization at the scale of large eddies, and ensuring local and global tracer mass conservation. The study objective was to resolve small dynamical processes inclusive of spatio-temporal scales of high-speed (e.g. 100 m s−1) airborne measurements. This was achieved by downscaling of reanalysis data from 31.25 km to 50 m through multi-domain model nesting in the horizontal and grid-refining in the vertical. Further, WRF dynamical-solver source code was modified to simulate the release of passive tracers within the finest-resolution domain. Different meteorological case studies and several tracer source emission scenarios were considered. Model-generated fields were evaluated against observational data (surface monitoring network and aircraft campaign data) and also in terms of tracer mass conservation. Results indicated agreement between modelled and observed values within 5 ∘C for temperature, 1 %–25 % for relative humidity, and 1–2 standard deviations for wind fields. Model performance in terms of (global and local) tracer mass conservation was within 2 % to 5 % of model input emissions. We found that, to ensure mass conservation within the modelling domain, tracers should be released on a regular-resolution grid (vertical and horizontal). Further, using our super-resolution modelling products, we investigated emission rate estimations based on flux calculation and mass-balancing. Our results indicate that retrievals under weak advection conditions (horizontal wind speeds &lt; 5 m s−1) are not reliable due to weak correlation between the source emission rate and the downwind tracer mass flux. In this work we demonstrate the development of accurate super-resolution model simulations useful for planning, interpreting, and optimizing top-down retrievals, and we discuss favourable conditions (e.g. meteorological) for reliable mass-balance emission rate estimations.

A Case Study of Air Quality and a Health Index over a Port, an Urban and a High-Traffic Location in Rhodes City

One of people’s greatest concerns about air quality degradation is its impact on human health. This work is a case study that aims to investigate the air quality and the related impact on people’s health in a coastal city over the eastern Mediterranean. The analysis proceeded during a low-tourist density period, covering the days from 17 to 27 November 2022. Hourly PM2.5, NO2 and O3 concentration records from three, mobile, Air Quality Monitoring Systems (AQMS), established in an urban location, port and central area of Rhodes city, are analyzed. To investigate the impact of pollution levels on human health, the Air Quality Health Index (AQHI) is calculated. The daily and diurnal variation of pollutants’ concentration and AQHI among the different areas, as well as the relation among the ambient air pollutants and AQHI, are studied. Additionally, to investigate the impact of wind regime on the variation of pollution and AQHI levels, the hourly zonal and meridional wind-speed components, as well as the temperature at 2 m, the dew point temperature at 2 m, and the height of the boundary layer from ERA5 reanalysis, are retrieved for the region of the southeastern Mediterranean. Results show that the highest pollution level occurs in the city center of Rhodes, compared to the rest of the studied locations. In general, the findings do not show exceedances of the pollutants’ concentration according to the European Directive 2008/50/EC. Moreover, findings show that in some cases, the health risk is classified from Low to Moderate in terms of AQHI. The analysis indicates that the climate conditions affect the pollutants’ concentration due to dispersion, and likely, the atmospheric transport of pollutants. Finally, this work aims to improve the knowledge regarding the air quality of southeastern Greece, promoting the framework for the green and sustainable development of the South Aegean Sea.

Empirical mode decomposition of the atmospheric flows and pollutant transport over real urban morphology

The momentum transport and pollutant dispersion in the atmospheric surface layer (ASL) are governed by a broad spectrum of turbulence structures. Whereas, their contributions have not been explicitly investigated in the context of real urban morphology. This paper aims to elucidate the contributions from different types of eddies in the ASL over a dense city to provide the reference of urban planning, realizing more favorable ventilation and pollutant dispersion. The building-resolved large-eddy simulation dataset of winds and pollutants over the Kowloon downtown, Hong Kong, is decomposed into a few intrinsic mode functions (IMFs) via empirical mode decomposition (EMD). EMD is a data-driven algorithm that has been successfully implemented in many research fields. The results show that four IMFs are generally enough to capture most of the turbulence structures in real urban ASL. In particular, the first two IMFs, which are initiated by individual buildings, capture the small-scale vortex packets that populate within the irregular building clusters. On the other hand, the third and fourth IMFs capture the large-scale motions (LSMs) detached to the ground surface that are highly efficient in transport. They collectively contribute to nearly 40% of vertical momentum transport even with relatively low vertical turbulence kinetic energy (TKE). LSMs are long, streaky structures that mainly consist of streamwise TKE components. It is found that the open areas and regular streets promote the portion of streamwise TKE in LSMs, improving the vertical momentum transport and pollutant dispersion. In addition, these streaky LSMs are found to play a crucial role in pollutant dilution in the near field after the pollutant source, while the small-scale vortex packets are more efficient in transport in the mid-field and far-field.

Gaseous polycyclic aromatic hydrocarbons over the South China Sea: Implications for atmospheric transport under monsoon influences

The seasonal monsoon variations have significant impact on the atmospheric transport of semi-volatile organic pollutants over the South China Sea (SCS). We analyzed polycyclic aromatic hydrocarbons (PAHs) over the basin and island areas (Yongxing Island and Yongshu Island) in 2017. Gaseous PAHs (0.17–1.4 ng m−3) showed spatio-temporal distinctions in their composition and sources among the basin and island areas. Mixed combustion sources of PAHs were identified over the SCS, including a petroleum source near the island areas. The transport routes of PAHs were inferred by the air mass back trajectories and potential source contribution factor analysis, identifying strong biomass burning signals from the Indochina Peninsula and other Southeast Asian countries. Emissions from approximately 90 % of the combustion sources were transported to basin areas by monsoons, whereas the island areas were dominated by local emissions. This study emphasizes the main potential terrestrial source of PAHs over the SCS under monsoon influences.

A Century Ammonium Record Retrieved From the Central Tibetan Plateau

AbstractThe limited observations pose challenges to understanding long‐term variations of atmospheric ammonium () deposition. Glaciers on the margins of the Tibetan Plateau (TP) adjacent to heavily populated regions can capture and preserve unique records of natural and anthropogenic ammonium aerosol. However, relatively little has been known about spatiotemporal variations and anthropogenic influences on ammonium deposition on the central TP. Here, we present a high‐resolution ammonium record spanning the period 1900–2011, reconstructed from the Qiangtang (QT) ice core on the central TP. Empirical orthogonal function and interspecies correlation analysis reveal that has a source and/or transport route that differs from the dust species, especially after the 1950s. The QT ammonium record is also likely influenced by temperature‐dependent biogenic emissions from northwestern South Asia. Comparison with other ice core records shows that intensified anthropogenic emissions have caused a widespread increase in ammonium records in the inner TP after the 1950s. Furthermore, the significant positive relationship with the December–April Arctic Oscillation (AO) suggests that enhanced westerlies during the positive AO phase transport aerosol more efficiently to the QT. As a result, the decrease in ammonium concentrations after 1990, when anthropogenic emissions were still increasing, could be attributed to the weakening of westerlies associated with the transitioning of the AO phase from positive to negative. Our results may enhance the understanding of the influence of the westerlies on the transport of atmospheric pollutants to the central TP.

Potential impact of shipping on air pollution in the Mediterranean region – a multimodel evaluation: comparison of photooxidants NO2 and O3

Abstract. Shipping has a significant share in the emissions of air pollutants such as NOx and particulate matter (PM), and the global maritime transport volumes are projected to increase further in the future. The major route for short sea shipping within Europe and the main shipping route between Europe and East Asia are found in the Mediterranean Sea. Thus, it is a highly frequented shipping area, and high levels of air pollutants with significant potential impacts from shipping emissions are observed at monitoring stations in many cities along the Mediterranean coast. The present study is part of the EU H2020 project SCIPPER (Shipping contribution to Inland Pollution Push for the Enforcement of Regulations). Five different regional chemistry transport models (CAMx – Comprehensive Air Quality Model with Extensions, CHIMERE, CMAQ, EMEP – European Monitoring and Evaluation Programme, LOTOS-EUROS) were used to simulate the transport, chemical transformation and fate of atmospheric pollutants in the Mediterranean Sea for 2015. Shipping emissions were calculated with the Ship Traffic Emission Assessment Model (STEAM) version 3.3.0, and land-based emissions were taken from the CAMS-REG v2.2.1 dataset for a domain covering the Mediterranean Sea at a resolution of 12 km × 12 km (or 0.1∘×0.1∘). All models used their standard setup for further input. The potential impact of ships was calculated with the zero-out method. The model results were compared to each other and to measured background data at monitoring stations. The model results differ regarding the time series and pattern but are similar concerning the overall underestimation of NO2 and overestimation of O3. The potential impact from ships on the total NO2 concentration was especially high on the main shipping routes and in coastal regions (25 % to 85 %). The potential impact from ships on the total O3 concentration was lowest in regions with the highest NO2 impact (down to −20%). CAMx and CHIMERE simulated the highest potential impacts of ships on the NO2 and O3 air concentrations. Additionally, the strongest correlation was found between CAMx and CHIMERE, which can be traced back to the use of the same meteorological input data. The other models used different meteorological input due to their standard setup. The CMAQ-, EMEP- and LOTOS-EUROS-simulated values were within one range for the NO2 and O3 air concentrations. Regarding simulated deposition, larger differences between the models were found when compared to air concentration. These uncertainties and deviations between models are caused by deposition mechanisms, which are unique within each model. A reliable output from models simulating ships' potential impacts can be expected for air concentrations of NO2 and O3.

"Urban Respiration" Revealed by Atmospheric O2 Measurements in an Industrial Metropolis.

Urban regions, which "inhale" O2 from the air and "exhale" CO2 and atmospheric pollutants, including harmful gases and fine particles, are the largest sinks of atmospheric O2, yet long-term O2 measurements in urban regions are currently lacking. In this study, we report continuous measurements of atmospheric O2 in downtown Lanzhou, an industrial metropolis in northwestern China. We found declines in atmospheric O2 associated with deteriorated air quality and robust anticorrelations between O2 and gaseous oxides. By combining O2 and pollutants measurements with a Lagrangian atmospheric transport model, we quantitatively break down "urban respiration" (ΔO2URB) into human respiration (ΔO2RES) and fossil fuel combustion (ΔO2FF). We found increased ΔO2FF contribution (from 66.92% to 72.50%) and decreased ΔO2RES contribution (from 33.08 to 27.50%) as O2 declines and pollutants accumulate. Further attribution of ΔO2FF reveals intracity transport of atmospheric pollutants from industrial sectors and suggests transportation sectors as the major O2 sink in downtown Lanzhou. The varying relationships between O2 and pollutants under different conditions unfold the dynamics of urban respiration and provide insights into the O2 and energy consumption, pollutant emission, and intracity atmospheric transport processes.

Gaseous and soil OCPs and PCBs along the Indus River, Pakistan: spatial patterns and air-soil gradients.

This study presents first-hand information on the occurrence of persistent organic pollutants (POPs) in the ambient air and surface soil along the Indus flood-plain, Pakistan. The sampling campaign was conducted at 15 site locations during 2014-15, along the Indus River (approximately 1300 km). Composite surface soil samples (N = 15) and passive air samples (N = 15) were collected for the estimation of gaseous POPs as well as air-soil exchange to evaluate the POP emission and distribution or dispersion patterns, source tracking, and contribution of the local and regional sources towards POP accumulation in the Indus River system. Among the studied POPs, levels of DDTs and PCBs were noticeably higher in ambient air (50-560 and 10-1100 pg m-3) and in soil (0.20-350 and 1.40-20 ng g-1), respectively. Regarding the spatial patterns, higher DDT concentrations (ng g-1) were detected in the air and soil samples collected from the wet mountain zone (WMZ) (p < 0.05), followed by the alluvial riverine zone (ARZ), low-lying mountain zone (LLZ), and frozen mountain zone (FMZ). The PCB data did not exhibit significant differences (p > 0.05) for the air samples, while PCB concentrations were significantly higher (p < 0.05) in soil from the LLZ, which may be associated with rapid urbanization and industrial activities in this area. The air-soil exchange of DDTs and PCBs showed net volatilization at most of the studied sites except for a few samples from the FMZ and WMZ. Results of this study about air-soil exchange gradients indicate the long range regional atmospheric transport (LRAT) of POPs to the colder areas (FMZ) of Pakistan, where these act as a secondary source of POPs in these areas.

Weather-Climate Anomalies and Regional Transport Contribute to Air Pollution in Northern China During the COVID-19 Lockdown.

Two persistent and heavy haze episodes during the COVID-19 lockdown (from 20 Jan to 22 Feb 2020) still occur in northern China, when anthropogenic emissions, particularly from transportation sources, are greatly reduced. To investigate the underlying cause, this study comprehensively uses in-situ measurements for ambient surface pollutants, reanalysis meteorological data and the WRF-Chem model to calculate the contribution of NOx emission change and weather-climate change to the "unexpectedly heavy" haze. Results show that a substantial NOx reduction has slightly decreased PM2.5 concentration. By contrast, the weakest East Asian winter monsoon (EAWM) in the 2019-2020 winter relative to the past decade is particularly important for haze occurrence. A warmer and moister climate is also favorable. Model results suggest that climate anomalies lead to a 25-50μgm-3 increase of PM2.5 concentration, and atmospheric transport is also an important contributor to two haze episodes. The first haze is closely related to the atmospheric transport of pollutants from NEC to the south, and fireworks emissions in NEC are a possible amplifying factor that warrants future studies. The second one is caused by the convergence of a southerly wind and a mountain wind, resulting in an intra-regional transport within BTH, with a maximal PM2.5 increment of 50-100μgm-3. These results suggest that climate change and regional transport are of great importance to haze occurrence in China, even with significant emission reductions of pollutants.

Comparison of Planetary Boundary Layer Height Derived from Lidar in AD-Net and ECMWFs Reanalysis Data over East Asia

The planetary boundary layer height is a very important parameter in the atmosphere because it determines the range where the most effective dispersion processes take place, and it serves as a medium for the vertical transport of heat, moisture, and pollutants. The accurate estimation of boundary layer height (BLH) is vital for air pollution prediction. In this paper, the BLH estimated by AD-Net was compared with that from the ECMWFs over East Asia from September 2015 to August 2018. A continuous 24 h BLH estimation from AD-Net generally matched with the aerosol vertical structures. Diurnal and seasonal variation and spatial variation of BLH can also be shown, suggesting the good performance of AD-Net BLH. The comparison of seasonal mean BLH between AD-Net and ECMWFs was conducted at 20 lidar sites. On average, there was an underestimation of the ECMWFs, mostly in summer and winter. A significant disagreement between AD-Net and the ECMWFs was noted, especially over coastal areas and mountain areas. In order to investigate the difference between them, two BLHs were compared under different land cover types and climate conditions. In general, the BLH of the ECMWFs was less than that of AD-Net over most of the land cover types in summer and winter. The smallest differences (0.26 km) existed over water surfaces in winter compared with AD-Net, and the largest underestimation (1.42 km) occurred over grassland surfaces in summer. Similarly, all the BLHs of the ECMWFs were lesser than those of AD-Net under different climatological conditions in summer and winter. The mean difference between AD-Net BLH and ECMWFs BLH was 1.05, 0.71, and 0.48 km for arid regions, semi-arid and semi-wet regions, and wet regions, respectively. The largest underestimation occurred over arid regions in winter, with a value of 1.42 km. The smallest underestimation occurred over wet regions, with a value of 0.27 km. The present research provides better insight into the BLH performance in the ECMWFs reanalysis data. The new continuous PBL dataset can be used to improve the model parameterization of PBL and our understanding of the atmospheric transport of pollutants which affect air quality and human health.

Ambient particle characteristics by single particle aerosol mass spectrometry at a coastal site in Hong Kong: a case study affected by the sea-land breeze.

The sea-land breeze (SLB) circulation plays a vital role in the transport of atmospheric pollutants in coastal cities. In this study, a single particle aerosol mass spectrometer (SPAMS) and combined bulk aerosol instruments were deployed to investigate the ambient particle characteristic at a suburban coastal site in Hong Kong from February 22 to March 10, 2013. Significant SLB circulations were captured from March 6-10, 2013, during the campaign. During the SLB periods, air quality worsened, with PM2.5 concentrations reaching a peak of 55.6 μg m-3 and an average value of 42.8 ± 4.5 μg m-3. A total of 235,894 particles were measured during the SLB stage. Eight major sources were identified by investigating the mixing states of the total particles, including the coal-burning related particles (48.1%), biomass burning particles (6.7%), vehicle emission-related particles (16.4%), sea salt (9.2%), ship emission particles (2.7%), dust/steeling industries (3.7%), waste incineration (6.3%), and road dust (3.9%). It was noteworthy that the PM2.5 concentrations and particle numbers increased sharply during the transition of land wind to the sea breeze. Meanwhile, the continental sourced pollutants recirculated back to land resulting in a cumulative increase in pollutants. Both individual and bulk measurements support the above results, with high contributions from coal burning, biomass burning, bulk K+, and NO3 -, which were probably from the regional transportation from the nearby area. In contrast, the ship and vehicle emissions increased during the SLB period, with a high sulfate concentration partially originating from the ship emission. In this study, field evidence of continental-source pollutants backflow to land with the evolution of sea breeze was observed and helped our current understanding of the effect of SLB on air quality in the coastal city.