Backward Trajectories Research Articles

Chemical characteristics and formation mechanism of secondary inorganic aerosols: The decisive role of aerosol acidity and meteorological conditions

In recent years, there has been a growing concern about air pollution and its impact on the air quality and human health, especially for fine particulate matter (PM2.5) and its associated secondary aerosols in urban areas. This study conducted a year-long field campaign to collect PM2.5 samples day and night in an urban area of central Taiwan. Higher PM2.5 mass concentrations were observed in winter (27.7 ± 9.7 μg/m3), followed by autumn (22.5 ± 8.3 μg/m3), spring (19.2 ± 6.4 μg/m3), and summer (11.0 ± 3.1 μg/m3). The dominant formation mechanism of secondary inorganic aerosols was heterogeneous reactions of NO3− at night and homogeneous reactions of SO42− during the day. Additionally, significant correlations were observed between aerosol liquid water content (ALWC) and NO3− during nighttime, indicating the importance of aqueous-phase NO3− formation. The role of aerosol acidity was explored and a unique alkaline condition was found in spring and summer, which showed lower PM2.5 concentrations than the neutralized condition. Under the neutralized condition, higher PM2.5 concentrations were commonly found when combining the ammonium-rich regime with molar ratios of [NO3−]/[SO42−] exceeding 1.6, suggesting the importance of reducing both NH3 and NOx. Furthermore, the results showed that reducing NH3 should be prioritized under high temperature conditions, while reducing NOx became important under low temperature conditions. Clustering of backward trajectories showed that long-range transport could enhance the formation of secondary aerosols, but local emissions emerged as the main factor driving high PM2.5 concentrations. This study provides insights for policymakers to improve air quality, suggesting that different mitigation strategies should be formulated based on meteorological variables and that using clean energy for vehicles and electricity generation is important to alleviate air pollution.

Spatiotemporal variations of atmospheric mercury at urban and suburban areas in Southern Vietnam megacity: A preliminary year-round measurement study

Atmospheric mercury (Hg) pollution studies in peninsular Southeast Asia (PSEA) are currently experiencing shortage on spatiotemporal coverage due to limited observation data. Therefore, our study provided year-round (May 2022–April 2023) atmospheric Hg data at two urban and one suburban site in Ho Chi Minh City (HCMC) Vietnam - a megacity in PSEA. Higher total gaseous Hg (TGM) levels at 2 urban sites of 2.49 ± 0.86 ng m−3 (Nguyen Van Cu) and 2.12 ± 0.49 ng m−3 (Linh Trung) were observed as compared to the suburban site of 1.76 ± 0.50 ng m−3 (Can Gio) which suggests the influence of anthropogenic Hg sources. Higher TGM concentration in October 2022–January 2023 as opposed to May 2022–September 2022 at all 3 sites reflected the influence of abrupt change in air mass origins and transport pathways in southern Vietnam. Backward trajectories (BWTs) and concentration-weighted trajectory (CWT) models further suggested East Asian outflow from northeast (NE) direction as a prominent TGM source in HCMC. Our two case studies in June and December 2022 helped to distinguish the impacts of local accumulation besides long-range atmospheric Hg transport towards TGM levels in HCMC. We also attempted to address TGM public health concerns wherein a minimal hazard quotient (HQ < 1) implied insignificant Hg health risk via inhalation pathways. Our study strives to offer crucial information to fill the Hg data gap as well as seeks to explore the impact of monsoon drives on Hg pollution in the PSEA region.

Soil contamination caused by fly ash from coal-fired thermal power plants in India: Spatiotemporal distribution and elemental leaching potential

On combustion, coal produces fly ash (FA) and spheroidal carbonaceous particles (SCP) at high temperatures. Airborne particles like FA and SCP can be transported over long distances by wind, leading to the pollution of air and water resources. Concern mainly arises from various toxic metals loosely bound to the surface of FA and SCP. Here, we trace the provenance of SCP in soil samples collected upwind and downwind from two coal-fired thermal power plants (TPP) in central Nagpur (Khaperkheda and Koradi) that have been operational for over four decades. The samples showed morphological similarities between SCPs from soil samples and FA collected from the Khaperkheda power plant. The SCP distribution shows a sharp increase in the soil profiles coinciding with the expansion of the power plants between 2010 and 2015. Backward trajectories of winds were calculated to ascertain whether the sampling locations downwind of the TPPs were potentially affected by FA emissions. The results from the back trajectories indicate that emissions from the TPP are directed toward the sampling sites. Finally, leaching experiments were conducted in FA to assess the release of elements. Leaching experiments at 30, 40, and 50 °C and at a given pH or extraction time did not show any notable differences in elemental concentrations of Al, As, Ca, Cr, Co, Cu, Fe, Mn, Mo, Se, Ni, Ti, V, and Zn. The concentration of different elements mobilized from FA was high at pH 3, with rapid leaching occurring within the first 30 min of the experiment. Hence, disposal, reclamation, and management of FA need to be regulated and monitored correctly to ensure the safety of its use.

Temporal variations and chemical characteristics of marine PM2.5 at Dongsha Islands, South China Sea: Three-year measurement

The study of long-range transport effects on marine fine particles (PM2.5), particularly in remote sites such as the Dongsha Islands, is pivotal for advancing our understanding of air pollution dynamics on a regional scale and for formulating effective environmental policies. PM2.5 concentrations were examined over three consecutive years and grouped based on their transport routes. The backward trajectory simulation revealed that high PM2.5 concentrations were observed in the West Channel, originating from North and Central China, the Korean Peninsula, and the Japanese Islands, opposed to the East Channel. High PM2.5 concentrations, commonly observed in winter and spring, were mainly attributed to the Asian Northeastern Monsoons. Water-soluble inorganic ions constituted the major components, accounting for 37.8–48.7% of PM2.5, and followed by metal elements (15.5–20.0%), carbons (7.5–13.3%), levoglucosan (0.01–0.17%), and organic aerosols (0.2–2.2%). Secondary inorganic aerosols as the dominant source accounted for 8.3–24.7% of PM2.5, while sea salts were the secondary major contributor. High levoglucosan contribution (3.8–7.2%) in winter and spring was attributed to biomass burning, mainly from the Indochina Peninsula. Chemical mass balance receptor modeling resolved that major sources of PM2.5 were secondary sulfate, sea salts, fugitive dust, and industrial boilers. This study concluded that the long-range transport of PM2.5 gradually increased since fall, contributing 52.1–74.3%, highlighting its substantial impact on PM2.5 in all seasons except summer.

Short-term associations of PM10 attributed to biomass burning with respiratory and cardiovascular hospital admissions in Peninsular Malaysia.

Biomass burning (BB) is a major source of air pollution and particulate matter (PM) in Southeast Asia. However, the health effects of PM smaller than 10 µm (PM10) originating from BB may differ from those of other sources. This study aimed to estimate the short-term association of PM10 from BB with respiratory and cardiovascular hospital admissions in Peninsular Malaysia, a region often exposed to BB events. We obtained and analyzed daily data on hospital admissions, PM10 levels and BB days from five districts from 2005 to 2015. We identified BB days by evaluating the BB hotspots and backward wind trajectories. We estimated PM10 attributable to BB from the excess of the moving average of PM10 during days without BB hotspots. We fitted time-series quasi-Poisson regression models for each district and pooled them using meta-analyses. We adjusted for potential confounders and examined the lagged effects up to 3 days, and potential effect modification by age and sex. We analyzed 210960 respiratory and 178952 cardiovascular admissions. Almost 50% of days were identified as BB days, with a mean PM10 level of 53.1 µg/m3 during BB days and 40.1 µg/m3 during normal days. A 10 µg/m3 increment in PM10 from BB was associated with a 0.44% (95% CI: 0.06, 0.82%) increase in respiratory admissions at lag 0-1, with a stronger association in adults aged 15-64 years and females. We did not see any significant associations for cardiovascular admissions. Our findings suggest that short-term exposure to PM10 from BB increased the risk of respiratory hospitalizations in Peninsular Malaysia.

The Association Between Cloud Droplet Number over the Summer Southern Ocean and Air Mass History

AbstractThe cloud properties and governing processes in Southern Ocean marine boundary layer clouds have emerged as a central issue in understanding the Earth's climate sensitivity. While our understanding of Southern Ocean cloud feedbacks have evolved in the most recent climate model intercomparison, the background properties of simulated summertime clouds in the Southern Ocean are not consistent with measurements due to known biases in simulating cloud condensation nuclei concentrations. This paper presents several case studies collected during the Capricorn 2 and Marcus campaigns held aboard Australian research vessels in the Austral Summer of 2018. Combining the surface‐observed cases with MODIS data along forward and backward air mass trajectories, we demonstrate the evolution of cloud properties with time. These cases are consistent with multi‐year statistics showing that long trajectories of air masses over the Antarctic ice sheet are critical to creating high droplet number clouds in the high latitude summer Southern Ocean. We speculate that secondary aerosol production via the oxidation of biogenically derived aerosol precursor gasses over the high actinic flux region of the high latitude ice sheets is fundamental to maintaining relatively high droplet numbers in Southern Ocean clouds during Summer.

Air Composition over the Russian Arctic–4: Atmospheric Aerosols

This work presents the analysis of the spatial distribution of number concentration, size distribution, and chemical composition of aerosol particles measured for the first time over the seas of the Russian Arctic. Various types of vertical distribution of the number concentration were recorded, characteristic of both coastal marine and continental areas. Most of them turned out to be of the continental type. Attention is also drawn to the almost complete absence of coarse particles above 2–3 km over all seas. The chemical composition of the Arctic aerosol at altitudes of both 200 m and 5000 m contains ions that can be referred to as both marine and continental. The identifiable carbon- and salt-free elemental part of the aerosol over the Arctic is 3–4 times larger than that of ions. Over all seas and at both altitudes, the Arctic aerosols mainly contain elements of terrigenous origin – Al, Cu, Fe, and Si. Over almost all seas, except the Barents Sea, Si is dominant in the elemental composition of the aerosol, its contribution over the Chukchi Sea reaching 85%. The analysis of backward trajectories showed that in all cases considered, whether the aerosol was formed over the continent or sea, air trajectories passed both over sea and over land. In this case, the formed particles could be enriched with additional ions and elements along their pathway. This work completes a cycle of the papers, devoted to studying air composition, which was carried out over the seas of the Russian Arctic in September 2020. Our results can be used to model the atmospheric processes occurring in the Arctic under the conditions of changing climate.

A case study of surface ozone source contributions in the Seoul metropolitan area using the adjoint of CMAQ

ABSTRACT To quantitatively investigate the transboundary behaviors and source attributions of ozone (O3) and its precursor species over East Asia, we utilize the adjoint technique in the CMAQ modeling system (the CMAQ adjoint). Our focus is on the Seoul Metropolitan Area (SMA) in South Korea, which is the receptor region of this study. We examine the contributions of both local and transported emissions to an O3 exceedance episode observed on June 3, 2019, estimating up to four days in advance. By using the CMAQ adjoint, we can determine the sensitivity of O3 remaining in the SMA to changes in O3 precursor emissions (emissions-based sensitivity) and concentrations (concentrations-based sensitivity) along the long-range transport pathways and emission source regions overseas. These include Beijing-Tianjin-Hebei (BTH), Shandong, Yangtze River Delta (YRD), and Central China. CMAQ adjoint-derived source attributions suggest that overseas precursor emissions and O3 contributed significantly to the O3 exceedance event in SMA. The emissions-based sensitivities revealed that precursor emissions originating from Shandong, YRD, Central China, and BTH contributed 11.42 ppb, 4.28 ppb, 1.24 ppb, 0.9 ppb, respectively, to the O3 exceedance episode observed in the SMA. Meanwhile, Korean emissions contributed 31.1 ppb. Concentrations-based sensitivities indicated that 19.3 ppb of contributions originated in regions beyond eastern China and directly affected the O3 level in the SMA in the form of background O3. In addition to capturing the transboundary movements of air parcels between the source and receptor regions, we performed HYSPLIT backward trajectory analyses. The results align with the trajectories of O3 and its precursors that we obtained from the adjoint method. This study represents a unique effort in employing the adjoint technique to examine the impacts of regional O3 on South Korea, utilizing a combination of emissions-based and concentrations-based sensitivities. Implications: This research brings to light the critical role of both local and regional precursor emissions in contributing to an ozone (O3) exceedance event in the Seoul Metropolitan Area (SMA), South Korea. Utilizing the CMAQ adjoint technique, a novel approach in the context of South Korea’s O3 investigations, we were able to delineate the quantitative contributions of different regions, both within South Korea and from overseas areas such as Beijing, Shandong, Shanghai, and Central China. Importantly, the results underscore the substantial influence of transboundary pollutant transport, emphasizing the need for international collaboration in addressing air quality issues. As metropolitan areas around the globe grapple with similar challenges, the methodology and insights from this study offer a potent tool and framework for regions seeking to understand and mitigate the impacts of O3 on human health and the environment. By integrating different sensitivity types, coupled with HYSPLIT backward trajectory analyses, this research equips policymakers with comprehensive data to design targeted interventions, emphasizing the significance of collaborative efforts in tackling regional air pollution challenges. However, it’s important to note the limitation of this study, which is a case study conducted over a short time period. This constraint may impact the generalizability of the findings and suggests a need for further research to validate and expand upon these results.

Spatio-seasonal characteristics and controlling factors of surface water stable isotope values (δ18O and δD) across the Inner Mongolia Reaches of the Yellow River Basin, China: Implication for hydrological cycle

Study regionInner Mongolia Reaches of the Yellow River Basin (IMR-YRB) in China, knwon as the “Jiziwan” economic belt. Study focusHigh spatio-seasonal resolution sampling data of the surface waters in the IMR-YRB were applied (189 samples collected from 63 sites during the wet (July 2021), dry (October 2021) and normal (April 2022) seasons). The testing results of stable H and O isotopes were combined with backward wind trajectory modeling and geostatistical analysis to identify the spatio-seasonal characteristics of the surface water cycle and its controlling factors. New hydrological insights for the regionThe results showed that surface waters were mainly recharged by precipitation from summer monsoon, resulting in depleted isotopic contents (low δ18O and high d-excess) during the wet season. In contrast, most of the surface waters were characterized by isotopic enrichment (high δ18O and low d-excess) during the dry and normal seasons, which was attributed to the effects of continuous evaporation. In addition, there were some samples that exhibited isotopic depletion during the dry and normal seasons due to the effects of groundwater discharge or snowmelt recharge. Overall, this study improved the understanding of the surface water cycle at a large-scale basin for understanding hydrologic processes in other regions.

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.

Sources and distribution of trace elements in surface snow from coastal Zhongshan Station to Dome A (East Antarctica)

The spatial distribution and possible sources of Al, As, Cd, Fe, Mn, Pb, Sb, Ti, V, and Zn were investigated in 120 samples of surface snow collected along a ∼1260 km long traverse from coastal Zhongshan Station to the Antarctic ice sheet summit (Dome A or Dome Argus, at 4093 m a.s.l.). The chemical composition of snow samples was analyzed using microwave-assisted acid treatment with HNO3/HF to determine element concentrations, reflecting their abundance in the Earth's crust. The observed relative concentration pattern of elements in snow suggests a predominant contribution from soil and rock dust particles. The spatial distribution of total element concentrations along the traverse revealed higher values in inland areas compared to coastal areas. The annual deposition flux of elements in each sampling site indicates a significant decreasing trend in Al, Ti, Zn, Fe, Cd, As, and Pb from the coast to inland areas. Significant variations in element concentrations and fluxes observed along the Antarctic traverse suggest a notable influence of distance from the coast on snow deposition patterns. Soil dust from coastal ice-free areas and human activities in scientific stations are the primary sources of analyzed elements in coastal snow, with marine biogenic emissions playing a marginal role, likely contributing to As and Cd. The contribution of sea salt spray to surface snow element concentrations in the East Antarctic traverse is negligible. An analysis of backward trajectories confirmed that long-distance transport from the South American continent and local Antarctic research stations potentially contributes to Antarctic snow elements.

Urban air PCDD/Fs: Atmospheric concentrations, temporal changes, gas/particle partitioning, possible sources and cancer risks

Polychlorinated dibenzo-p-dioxins/furans (PCDD/Fs) are pollutants of concern due to their toxic effects. No active sampling study on PCDD/Fs has been conducted in Bursa. This study aimed to fill this gap by measuring PCDD/F levels in the region. Accordingly, the samples were collected from an urban area in Bursa, covering four seasons between June 2022 and April 2023. The total (gas+particulate) ambient air concentrations were between 312.23 and 829.80 fg/m3 (mean: 555.05 ± 173.62 fg/m3). In terms of toxic equivalents (TEQ), the average concentration was 43.29 ± 9.18 fg WHOTEQ/m3. Based on the concentration values obtained, cancer and non-carcinogenic risk values of PCDD/Fs were calculated for three different age groups. The results indicated negligible health risks for all age groups. In addition, a seasonal assessment was also made and it was observed that PCDD/F concentration values varied with the ambient air temperatures. In general, higher values were measured in colder months compared to warmer months. This was probably due to the additional sources and adverse meteorological conditions. Moreover, the gas/particle partitioning of PCDD/Fs was investigated in detail. The average gas and particulate phase concentrations for PCDD/Fs were 101.81 ± 20.77 and 453.24 ± 172.50, respectively. It was found that an equilibrium state was not reached in the gas/particle partitioning. Two different gas/particle partition models based on adsorption and absorption mechanisms were compared, and the absorption model gave more consistent predictions. The Principal Component Analysis (PCA) was employed to identify the possible PCDD/F sources. The results indicated that the region was influenced by vehicle emissions, residential heating, organized industrial zones and metal recycling facilities. In addition, 72-hour backward air mass trajectory analyses were performed to understand the long-range transported air masses. However, it was found that the transported air masses did not significantly affect the concentration values measured in the sampling site.

Phenomenology of the Composition of PM2.5 at an Urban Site in Northern France

In this work, PM2.5 was sampled at Dunkerque, a medium-sized city located in northern France. The mean concentration of PM2.5 during the sampling period was 12.6 ± 9.5 μg·m−3. Samples were analyzed for elemental and organic carbon (EC/OC), water-soluble organic carbon (WSOC), humic-like substances (HULIS-C), water-soluble inorganic ions, and major and trace elements. The origin and the variations of species concentrations were examined using elemental enrichment factors, bivariate polar plot representations, and diagnostic concentration ratios. Secondary inorganic ions were the most abundant species (36% of PM2.5), followed by OC (12.5% of PM2.5). Secondary organic carbon (SOC) concentrations were estimated to account for 52% of OC. A good correlation between SOC and WSOC indicated that secondary formation processes significantly contribute to the WSOC concentrations. HULIS-C also represents almost 50% of WSOC. The determination of diagnostic ratios revealed the influence of anthropogenic emission sources such as integrated steelworks and fuel oil combustion. The clustering of 72 h air masses backward trajectories data evidenced that higher concentrations of PM2.5, OC, and secondary inorganic aerosols were recorded when air masses came from north-eastern Europe and the French continental sector, showing the considerable impact of long-range transport on the air quality in northern France.

Consistent social information perceived in animated backgrounds improves ensemble perception of facial expressions.

Observers can rapidly extract the mean emotion from a set of faces with remarkable precision, known as ensemble coding. Previous studies have demonstrated that matched physical backgrounds improve the precision of ongoing ensemble tasks. However, it remains unknown whether this facilitation effect still occurs when matched social information is perceived from the backgrounds. In two experiments, participants decided whether the test face in the retrieving phase appeared more disgusted or neutral than the mean emotion of the face set in the encoding phase. Both phases were paired with task-irrelevant animated backgrounds, which included either the forward movement trajectory carrying the "cooperatively chasing" information, or the backward movement trajectory conveying no such chasing information. The backgrounds in the encoding and retrieving phases were either mismatched (i.e., forward and backward replays of the same trajectory), or matched (i.e., two identical forward movement trajectories in Experiment 1, or two different forward movement trajectories in Experiment 2). Participants in both experiments showed higher ensemble precisions and better discrimination sensitivities when backgrounds matched. The findings suggest that consistent social information perceived from memory-related context exerts a context-matching facilitation effect on ensemble coding and, more importantly, this effect is independent of consistent physical information.

Parameterized atmospheric oxidation capacity during summer at an urban site in Taiyuan and implications for O3 pollution control

In recent years, summer ozone pollution shows a significant upward trend in many cities of China, affecting human health and ecosystems. The atmospheric oxidation capacity (AOC) is the core driving force for converting primary pollutants into secondary pollutants. In order to better understand the characteristics of AOC in summer, the comprehensive observation of VOCs (including OVOCs) was conducted at an urban site in Taiyuan from July 20 to August 3, 2020. The parameterized analysis of AOC and ROH was carried out by combining with the simulated photolysis rates (JO1D, JNO2 and JNO3). The results showed that the mean value of MDA8 O3, AOC and ROH were 84.2 ppbv, 2.4 × 107 molecules cm−3 s−1 and 28.3 s−1, respectively. The major reductants of AOC were CO (37.6%), isoprene (21.7%) and formaldehyde (16.8%). Diurnal variations of AOC showed a peak at noon, the major oxidants for AOC were OH (97.7%) and O3 (78.7%) during the daytime and nighttime, respectively. The mean value of MDA8 O3, AOC and VOCs-AOC during the pollution period (MDA8 O3 > 75 ppbv) were 33.0%, 45.0% and 59.3% higher than the non-pollution period, respectively. The OH reactivity ratio of NOx and VOCs indicated that O3 formation occurred under a VOC-limited regime. The backward trajectory analysis showed that VOCs from southwestern airmass had the highest AOC (2.0 × 107 molecules cm−3 s−1), and the domain contributors were isoprene (39.0%), formaldehyde (24.9%), acetaldehyde (9.8%) and ethylene (4.4%). This study could provide some references for regulating AOC to alleviate O3 pollution.

Interaction of black carbon surface mass with meteorological variables and spatial pattern across the 36 states of tropical Nigeria

Black carbon (BC) has been linked to cardio-pulmonary diseases and lung cancer. It is also the second largest contributor to climate change, after carbon dioxide (CO2), Effective mitigation of BC is of much benefits, but it requires detailed knowledge of its spatial distribution, as well as the influence of local meteorology on the spread of the pollutant. Many countries in sub-Sahara Africa including Nigeria, lack data on BC level. There is also limited information on meteorological impact on BC spatial distribution. This study therefore assessed the spatial and temporal distribution of BC across the 36 states of Nigeria and the influence of meteorology on the pollutant spread. Data on BC surface mass (BCMASS) and seven meteorological variables (air temperature, relative humidity, rainfall, wind speed, planetary boundary layer height (PBLH), atmospheric pressure and wind direction) were obtained from Modern Era Retrospective analysis for Research (MERRA-2). Spatial distribution of BCSMASS across 36 states of Nigeria, and interaction with meteorology was studied using correlation analyses, Bayesian ridge regression with marginal maximum likelihood estimation, and a Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model. There was significant (p < 0.05) variation in BCSMASS across the states. The meteorological variables, except wind direction, significantly influenced BCSMASS and they accounted for 63% of the variation. Five-day backward trajectory modelled for each month of the year revealed that northern Nigeria is majorly under the influence of the dry and dusty tropical continental wind, and this could partially account for the lower BCSMASS concentration in the region, compared to southern Nigeria. Based on population-weighted exposure, states in southern Nigeria, especially the south-eastern part, should be prioritized in planning mitigation, for effective climate action.

Pollution Characteristics, Source, and Health Risk Assessment of Metal Elements in PM2.5 Between Winter and Spring in Zhengzhou

A total of 18 metal elements in ambient PM2.5 in Zhengzhou were continuously determined using an online heavy metal observation instrument in January and April, 2021, and the changes in element concentrations were analyzed. Metal elements were traced via enrichment factors, positive matrix factorization (PMF), and a characteristic radar chart. The US EPA health risk assessment model was used to assess the health risks of heavy metals, and the backward trajectory method and the concentration-weighted trajectory (CWT) method were used to evaluate the potential source regions of health risks. The results showed that the element concentrations were higher in spring, and the sum of Fe, Ca, Si, and Al concentrations accounted for 89.8% and 87.5% of the total element concentrations in winter and spring, respectively. Cd was enriched significantly, which was related to human activities. The concentrations of Pb, Se, Zn, Ni, Sb, and K in winter and Cr, Ni, Fe, Mn, V, Ba, Ca, K, Si, and Al in spring increased with the increasing pollution level. The results of PMF and the characteristic radar chart showed that the main sources of metal elements in winter and spring were industry, crust, motor vehicles, and mixed combustion, with industry and mixed combustion pollution occurring more often in winter and crust pollution occurring more often in spring. Significant non-carcinogenic risks existed in both winter and spring with more severe health risks in winter, and Mn caused significant non-carcinogenic risks. The health risks in winter were mainly influenced by Zhengzhou and surrounding cities and long-distance transport in the northwest, and the health risks in spring were mainly influenced by Zhengzhou and surrounding cities.

Comprehensive analysis of metal(loid)s and associated metal(loid) resistance genes in atmospheric particulate matter

Despite global concerns about metal(loid)s in atmospheric particulate matter (PM), the presence of metal(loid) resistance genes (MRGs) in PM remains unknown. Therefore, we conducted a comprehensive investigation of the metal(loid)s and associated MRGs in PMs in two seasons (summer and winter) in Xiamen, China. According to the geoaccumulation index (Igeo), most metal(loid)s, except for V and Mn, exhibited enrichment in PM, suggesting potential anthropogenic sources. By employing Positive Matrix Factorization (PMF) model, utilizing a dataset encompassing both total and bioaccessible metal(loid)s, along with backward trajectory simulations, traffic emissions were determined to be the primary potential contributor of metal(loid)s in summer, whereas coal combustion was observed to have a dominant contribution in winter. The major contributor to the carcinogenic risk of metal(loid)s in both summer and winter was predominantly attributed to coal combustion, which serves as the main source of bioaccessible Cr. Bacterial communities within PMs showed lower diversity and network complexity in summer than in winter, with Pseudomonadales being the dominant order. Abundant MRGs, including the As(III) S-adenosylmethionine methyltransferase gene (arsM), Cu(I)-translocating P-type ATPase gene (copA), Zn(II)/Cd(II)/Pb(II)-translocating P-type ATPase gene (zntA), and Zn(II)-translocating P-type ATPase gene (ziaA), were detected within the PMs. Seasonal variations were observed for the metal(loid) concentration, bacterial community structure, and MRG abundance. The bacterial community composition and MRG abundance within PMs were primarily influenced by temperature, rather than metal(loid)s. This research offers novel perspectives on the occurrence of metal(loid)s and MRGs in PMs, thereby contributing to the control of air pollution.

The investigation of retrieval method for aerosol and water vapor profiles based on MAX-DOAS technology

Simultaneously obtaining the vertical distribution and profile of aerosol and water vapor is crucial for in-depth understanding of the Earth's radiation balance, regional water cycle, and the causes of frequent haze weather in China. This study developed a system and inversion method based on multi-axis differential optical absorption spectroscopy (MAX-DOAS) to simultaneously retrieve tropospheric aerosol and water vapor profiles. The absorption of dioxy (O4) was obtained by multi-elevation measurement using the developed ground-based MAX-DOAS system. By minimizing a cost function combining an atmospheric radiative transfer model, aerosol extinction profiles were first inverted, followed by water vapor profiles. Optimized parameter selection in the look-up table method reduced reliance on prior profile information, enhancing pollutant distribution retrieval accuracy. In the monitoring period in Huaibei region, aerosols were mainly below 1.5 km, while water vapor concentrations decreased with altitude. Comparisons of water vapor vertical column densities (VCDs) retrieved through the look-up table method with the European Centre for Medium-Range Weather Forecasts(ECMWF) ERA5 model and geometric approximation showed good agreement, with correlation coefficients of 0.93 and 0.98, respectively. To comprehend water vapor sources at various vertical layers, a 24-h backward trajectory clustering analysis was conducted using the HYSPLIT model based on observed wind fields. Findings revealed that at 500 m altitude, water vapor primarily emanated from the southeast, whereas at 1 km and 2 km altitudes, it predominantly originated from the southwest. The study advances simultaneous tropospheric aerosol and water vapor profile retrieval, providing reliable technical support for the investigation of regional pollution.

Anthropogenic sources and air mass transport affect spatial and seasonal variations of ambient halocarbons in southeastern China

Halocarbons play a vital role in ozone depletion and global warming, and are regulated by the Montreal Protocol (MP) and its amendments. China has been identified as an important contributor to the halocarbon emissions, but the regional sources of halocarbons in China are not yet well comprehended. To investigate the characteristics, emissions, and source profiles, this study conducted a field campaign in Xiamen, a coastal city in southeastern China. Higher enhancements were found in the unregulated halocarbons (CH3Cl, CH2Cl2, CHCl3) than in the MP eliminated species (CCl4, CH3Br) and the MP controlled species (HCFCs, HFCs). Many of the measured halocarbons varied seasonally and regionally, depending on the anthropogenic sources and atmospheric transport. Backward trajectory analysis showed that the air masses from inland were polluted over Shandong, Hebei, and northern Fujian in the cold season, while the air masses from the sea in the warm season were clean. Different air masses in two seasons were associated with the halocarbon patterns in the study area. Industrial activities, especially solvent usage, were the primary sources of halocarbons. The emission hot spots in Fujian Province were concentrated in Sanming, Fuzhou, and Xiamen, and the unregulated halocarbons made the largest contribution. This study provides an insight for a deep understanding of the characteristics and potential sources of halocarbons, and for strengthened management of halocarbons in China.