Concentration Weighted Trajectory Research Articles

Black carbon aerosol quantification over north-west Himalayas: Seasonal heterogeneity, source apportionment and radiative forcing

Continuous measurements of Black Carbon (BC) aerosol mass concentrations were carried at Dehradun (30.33°N, 78.04°E, 700 m amsl), a semi-urban site in the foothills of north-westHimalayas, India during January 2011–December 2017. We reported both the BC seasonal variations as well as mass concentrations from fossil fuel combustion (BCff) and biomass burning (BCbb) sources. Annual mean BC exhibited a strong seasonal variability with maxima during winter (4.86 ± 0.78 μg m−3) followed by autumn (4.18 ± 0.54 μg m−3), spring (3.93 ± 0.75 μg m−3) and minima during summer (2.41 ± 0.66 μg m−3). Annual averaged BC mass concentrations were 3.85 ± 1.16 μg m−3 varying from 3.29 to 4.37 μg m−3 whereas BCff and BCbb ranged from 0.11 to 7.12 μg m−3 and 0.13–3.6 μg m−3. The percentage contributions from BCff and BCbb to total BC are 66% and 34% respectively, indicating relatively higher contribution from biomass burning as compared to other locations in India. This is explained using potential source contribution function (PSCF) and concentration weighted trajectories (CWT) analysis which reveals the potential sources of BC originating from the north-west and eastern parts of IGP and the western part of the Himalayas that are mostly crop residue burning and forest fire regions in India. The annual mean ARF at top-of-atmosphere (TOA), at surface (SUR), and within the atmosphere (ATM) were found to be −14.84 Wm−2, −43.41 Wm−2, and +28.57 Wm−2 respectively. To understand the impact of columnar aerosol burden on ARF, the radiative forcing efficiency (ARFE) was estimated and averaged values were −31.81, −91.63 and 59.82 Wm−2 τ−1 for TOA, SUR and ATM respectively. The high ARFE within the atmosphere indicates the dominance of absorbing aerosol (BC and dust) over Northwest Himalayas.

Characteristics of PM2.5 at a High-Altitude Remote Site in the Southeastern Margin of the Tibetan Plateau in Premonsoon Season

The Tibetan Plateau (TP) is one of the world’s most sensitive areas for climate change. Previous studies have revealed that air pollutants emitted from South and Southeast Asia can be transported to and have a negative impact on the TP. However, the majority of the investigators have focused on the pollutant transport processes from South Asian regions (i.e., India and Bangladesh) and parts of Southeast Asia, while the regions adjacent to the southeast fringe of the TP (i.e., Burma and the Sino-Burmese border) have been neglected. Here, fine particulate matter (PM2.5) samples were collected during the period 11 March to 13 May 2018 at Gaomeigu, a high-altitude remote site in the southeastern margin of the TP. Characteristics, sources of PM2.5, and the potential source regions for different chemical components were investigated. During the sampling time, PM2.5 mass loadings ranged from 3.79 to 54.57 µg m−3, with an arithmetic mean concentration of 20.99 ± 9.80 µg m−3. In general, major peaks of organic carbon (OC) and elemental carbon (EC) always coincided with high loadings of K+ and NO3−, which implies that common combustion sources caused these species’ concentrations to covary, while the daily variations of crustal elements showed different trends with the other chemical compositions, suggesting different source regions for crustal materials. Five source factors were identified as possible aerosol sources for PM2.5 by positive matrix factorization (PMF). They are the mining industry (5.3%), characterized by heavy metal elements; secondary formation (18.8%), described by the high concentrations of NH4+ and SO42−; traffic-related emissions (26.7%), dominated by carbonaceous species (especially soot-EC) and some metal elements; fugitive dust (15.2%), represented by crustal elements (Ti, Fe, and Mn), Ca2+, and Mg2+; and biomass burning (34.0%), which is typified by high concentrations of K+, NO3−, char-EC, primary OC, and secondary OC. The concentration-weighted trajectory (CWT) analysis results showed that the northeast part of Burma is the potential source region for high concentrations of EC and NO3− due to biomass burning emissions, while the tourism industry surrounding Gaomeigu gave strong grid cell values of SO42− as well as moderate values of EC and NO3−. Moreover, the mining industry in the southwest direction of Gaomeigu has important impacts on the zinc concentrations.

Temporal variation and long–range transport of gaseous elemental mercury (GEM) over a coastal site of East China

Continuous measurements of gaseous elemental mercury (GEM) play a key role in identifying mercury sources and its behavior in the atmosphere. In order to investigate the characteristics of GEM during the year when Minamata Convention on Mercury has entered into force in China, concentrations of GEM along with other pollutants were continuously measured at a coastal site in Ningbo, China. Hourly mean concentration of GEM at the study site ranged from 0.64 to 13.58 ng m−3 and showed an annual mean of 2.44 ± 0.95 ng m−3. The atmospheric GEM showed obvious seasonal variations, with the highest seasonal average concentration in winter (2.62 ± 1.05 ng m−3) and the lowest value in summer (2.26 ± 0.78 ng m−3). The monthly variation of GEM/TGM ratios ranged from 72.6% to 98.0% and clear inverse trends for monthly GEM/TGM and O3 were found during the entire period. Higher O3 concentration promote the photochemical oxidation of GEM into divalent mercury. Additionally, a high GEM episode that lasted >3 days was analyzed, and it showing high correlation with PM2.5 and SO2. The dilution of marine airflow and enhanced oxidation of GEM over sea are important for GEM depletion at the coastal site. Smoothed concentration weighted trajectory (CWT) analysis revealed that the GEM at the study site was mainly impacted by anthropogenic emissions from coastal provinces (Fujian, Jiangsu and Zhejiang) and inland provinces (Jiangxi, Anhui and Hubei). Coordinated inter-regional control on pollutant emissions is essential for the mercury reduction in the study area.

Analysis of the atmospheric pollution transport pathways and sources in Shenyang, based on the HYSPLIT model

The transport pathways and potential sources distribution of air pollutants are statistically analyzed based on the Hybrid Single–Particle Lagrangian Integrated Trajectory (HYSPLIT) model and the TrajStat method driven by the meteorological data of the Global Data Assimilation System (GDAS), and the concentration monitoring data of PM10, PM2.5, SO2 and NO2 in Shenyang, Liaoning Province in 2017. The trajectory classification method is used to analyze the main transport pathways affecting air masses during the research period. It is considered that the air masses in the northeast and northwest directions are the main reason for the high concentration of pollutants in the study area, while the air masses in the south direction are considered to be clean. Furthermore, the results of PSCF (potential resource contribution function) are consistent with the results of CWT (concentration–weighted trajectory). The potential sources that result in high concentrations of PM10 and PM2.5 are mainly located in southern Hebei Province, northern Shandong Province and the central and eastern Inner Mongolia Autonomous Regions. The corresponding potential source area shows a concentration of PM10 exceeding 150 μg•m−3 and PM2.5 exceeding 75 μg•m−3, while the source of nitrogen sulfide is mainly influenced by local sources.

Characterization and source apportionment of black carbon aerosol in the Nanjing Jiangbei New Area based on two years of measurements from Aethalometer

Black carbon (BC) aerosols were measured using a seven channel Aethalometer at a suburban site of Nanjing, East China from January 2015 to December 2016 to study its temporal variations and quantify the magnitude of BC from fossil fuel (BCff) and biomass burning (BCbb) sources. The mean BC mass concentration was observed to be 2200 ± 1309 ng/m3 at the sampling site during the entire observation period, with the highest (lowest) concentrations found in the winter (summer and spring). A distinct diurnal variations in BC revealed with two maximum peaks occurred between 06:00 and 09:00 local time (LT) and 19:00 and 22:00 LT in all four seasons, was correlated with source emissions, meteorology, and dynamics of the atmospheric boundary layer. A significant seasonality was observed in the absorption Ångström exponent (α) with higher in spring and winter seasons, and lower during the summer. Further, it is evident that the contribution of BCff (BCff%) dominated during the observation period with the mean contributions of BCff % and BCbb% to the BC were found to be ~81% and 19%, respectively. Similar to α, BCbb% also exhibited high fractions in spring and winter suggests an enhanced contribution from biomass burning sources, and a low in summer. The results from both the potential source contribution function (PSCF) and concentration weighted trajectory (CWT) models indicated that the air masses originating from the northern Zhejiang and Anhui provinces were the potential source areas responsible for the high BC concentrations attributed from agricultural waste burning in Nanjing.

The characteristics and local-regional contributions of atmospheric black carbon over urban and suburban locations in Shanghai, China

Black carbon (BC), produced from the incomplete combustion of carbonaceous fuels, has emerged as a major contributor to global climate change with adverse health effects. Based on one-year (2016.06.01–2017.06.30) equivalent black carbon (eBC) measurements, this study analyzed the characteristics of eBC concentrations and the local-regional contributions at an urban site (Pudong, PD) and a suburban site (Qingpu, QP) in Shanghai, China. The results showed that the annual average eBC concentrations were 1.17 ± 0.61 μg m−3 and 2.09 ± 0.97 μg m−3 at PD and QP, respectively. The high eBC concentrations occurred in winter and at weekends both for PD and QP. There were significant negative correlation coefficients between the daily eBC, the daily wind speed (WS) and the daily boundary layer height (BLH) at PD (rws: 0.45, rblh = −0.35, p < 0.01) and QP (rws: 0.49, rblh = −0.32, p < 0.01). And the relative higher eBC concentrations coincided with southerly, southwesterly and westerly winds although these winds had lower frequencies. This could be related to the agricultural fire in these directions during summer harvesttime. The significant partial correlation coefficients of eBC-CO (ru:0.37–0.64, rs:0.18–0.44, p < 0.01) and eBC-NO2 (ru:0.49–0.74, rs:0.38–0.75, p < 0.01) could suggest that eBC mainly come from vehicular exhaust emissions in Shanghai. Besides, the higher eBC/PM2.5 (5.29% ± 1.94%) and eBC/CO(0.30% ± 0.14%) at QP indicated the more combustion activities and diesel-powered vehicle emissions in suburban areas. The concentration weighted trajectory (CWT) analysis indicated that the surrounding areas at the junction of Shanghai, Jiangsu, and Zhejiang provinces seemed to be relatively the most important sources outside of Shanghai.

Analysis of Air Pollution Characteristics and Meteorological Conditions in Zhengzhou from 2014 to 2017

Online monitoring data of atmospheric pollutants and meteorological parameters in Zhengzhou from 2014 to 2017 were collected to analyze the concentration levels, seasonal variations, and the ratio characteristics of atmospheric pollutants, as well as the effects of meteorological conditions on these pollutants. Results show that the annual average concentrations of PM2.5 and PM10 in the four years were (88±49.8), (95.8±60.2), (78.6±70.3), and (72.0±53.5) μg·m-3, and (158.5±65.3), (167.7±82.6), (144.5±91.5), and (132.7±70.3) μg·m-3, respectively, and were approximately two times higher than the grade Ⅱ annual limits set by China. Fuel combustion and the formation of secondary pollutants were the main sources of PM2.5 in Zhengzhou. Moreover, the contribution of coal combustion was found to be decreased, while that of traffic sources increased year by year. Low wind speed, high humidity, and reduced precipitation are important meteorological factors that contribute to serious air pollution. In addition, the Potential Source Contribution Function and the Concentration-Weighted Trajectory were used to analyze the potential sources, and the contribution of these sources to the distribution of PM2.5. The potential source areas of PM2.5 were mainly distributed in neighboring cities and provinces, such as Shanxi, Shaanxi, Hubei, Shandong, and Hebei. The short-distance transmission was found to contribute significantly to the mass concentration of PM2.5.

Transport pathways of PM10 during the spring in northwest China and its characteristics of potential dust sources

Abstract Dust storms that occur frequently during the spring in the arid and semiarid regions of northwest China can significantly increase PM10 loadings in the local area and its surroundings, and impair environmental ecology, human activity and health. Based on the monitoring data of PM10 and backward trajectories of air parcels calculated by the Hybrid Single Particle Lagrangian Integrated Trajectory model in Jiayuguan, Jinchang and Lanzhou during the spring seasons from 2014 to 2017, trajectory cluster analysis was used to identify the major transport pathways of PM10, and concentration-weighted trajectory and trajectory sector analysis were applied to identify the potential sources and quantify regional transported contributions. The results showed that there were major transport pathways coming from three directions: the northwestern pathways (for Jinchang and Lanzhou), the western pathways (for Jiayuguan and Lanzhou), and the northern pathways (for Jiayuguan and Jinchang). The corresponding potential dust sources for these pathways were the northwesterly sources, the westerly sources and the northerly sources, respectively. In addition, the northern Tibetan Plateau was another important source affecting Jiayuguan. There were distinct differences among the regional transport contributions from various directions. The PM10 concentrations (percentages) that exogenous dust sources contributed to Jiayuguan, Jinchang and Lanzhou decreased in a sequence from west to east at 47 μg/m3 (29.8%), 40 μg/m3 (27.1%) and 26 μg/m3 (17.3%), respectively, which were attributed predominantly to the long-range transport of dust sources with the remainder coming from local or nearby emissions. The above decreasing tendency was in accordance with the distance effect from the dust sources to the receptor sites.

Contrasting Aerosol Optical Characteristics and Source Regions During Summer and Winter Pollution Episodes in Nanjing, China

Two episodes with heavy air pollution in Nanjing, China, one in the summer and another one in the winter of 2017, were selected to study aerosol properties using sun photometer and ground-based measurements, together with source region analysis. The aerosol properties, the meteorological conditions, and the source regions during these two episodes were very different. The episodes were selected based on the air quality index (AQI), which reached a maximum value of 193 during the summer episode (26 May–3 June) and 304 during the winter episode (21–31 December). The particulate matter (PM) concentrations during the winter episode reached maximum values for PM2.5/10 of 254 g m−3 and 345 g m−3, much higher than those during the summer (73 and 185 g m−3). In contrast, the value of aerosol optical depth (AOD) at 500 nm was higher during the summer episode (2.52 0.19) than during that in the winter (1.38 0.18). A high AOD value does not necessarily correspond to a high PM concentration but is also affected by factors, such as wind, Planetary Boundary Layer Height (PBLH), and relative humidity. The mean value of the Ångström Exponent (AE) varied from 0.91–1.42, suggesting that the aerosol is a mixture of invaded dust and black carbon. The absorption was stronger during the summer than during the winter, with a minimum value of the single scattering albedo (SSA) at 440 nm of 0.86 on 28 May. Low values of asymmetry factor (ASY) (0.65 at 440 nm and 0.58 at 1020 nm) suggest a large number of anthropogenic aerosols, which are absorbing fine-mode particles. The Imaginary part of the Refractive Index (IRI) was higher during the summer than during the winter, indicating there was absorbing aerosol during the summer. These differences in aerosol properties during the summer and winter episodes are discussed in terms of meteorological conditions and transport. The extreme values of PM and AOD were reached during both episodes in conditions with stable atmospheric stratification and low surface wind speed, which are conducive for the accumulation of pollutants. Potential source contribution function (PSCF) and concentration weighted trajectory (CWT) analysis show that fine mode absorbing aerosols dominate during the summer season, mainly due to emissions of local and near-by sources. In the winter, part of the air masses was arriving from arid/semi-arid regions (Shaanxi, Ningxia, Gansu, and Inner Mongolia provinces) covering long distances and transporting coarse particles to the study area, which increased the scattering characteristics of aerosols.

Approaches for identifying PM2.5 source types and source areas at a remote background site of South China in spring.

The receptor model is an effectively and widely used tool for analyzing the source of PM2.5, and its development and improvement have always been focused and challenged. In this study, approaches of source analysis is applied and compared. The PM2.5 samples were collected in spring of 2015 at a remote background site of Weizhou, South China and were analyzed for water-soluble ions, trace metals, and sugars. The 28 measurement species were introduced into the positive matrix factorization (PMF) and a non-negative matrix factorization (NMF) model for inter-comparison of PM2.5 prediction. Results showed that the NMF model is a more robust tool to identify source types and source apportionment in the case of a small sample size (n = 31). In NMF, four source variants were obtained as dust (15.6%), biomass combustion (11.8%), secondary formation (17.6%), and coal combustion (54.9%), corresponding to four main source areas. These were Southeast Asia, South China Sea, Taiwan Strait, as well as Pearl River Delta, respectively. The areas were distinguished based on hybrid receptor models, potential source contribution function (PSCF) and concentration weighted trajectory (CWT), by introducing the daily loadings of each source factor from NMF method. These model results were highly consistent with categorized chemical characteristics of PM2.5, suggesting that NMF linking with hybrid receptor models provides valuable implications for exploring source types and source areas of PM2.5. Meanwhile, biomass combustion and coal combustion comparably contributed to the high PM2.5 concentrations indicating control strategy in South China in spring.

Sources and Geographical Origins of PM10 in Metz (France) Using Oxalate as a Marker of Secondary Organic Aerosols by Positive Matrix Factorization Analysis

An original source apportionment study was conducted on atmospheric particles (PM10) collected in Metz, one of the largest cities of Eastern France. A Positive matrix factorization (PMF) analysis was applied to a sampling filter-based chemical dataset obtained for the April 2015 to January 2017 period. Nine factors were clearly identified, showing mainly contributions from anthropogenic sources of primary PM (19.2% and 16.1% for traffic and biomass burning, respectively) as well as secondary aerosols (12.3%, 14.5%, 21.8% for sulfate-, nitrate-, and oxalate-rich factors, respectively). Wood-burning aerosols exhibited strong temporal variations and contributed up to 30% of the PM mass fraction during winter, while primary traffic concentrations remained relatively constant throughout the year. These two sources are also the main contributors during observed PM10 pollution episodes. Furthermore, the dominance of the oxalate-rich factor among other secondary aerosol factors underlines the role of atmospheric processing to secondary organic aerosol loadings which are still poorly characterized in this region. Finally, Concentration-Weighted Trajectory (CWT) analysis were performed to investigate the geographical origins of the apportioned sources, notably illustrating a significant transport of both nitrate-rich and sulfate-rich factors from Northeastern Europe but also from the Balkan region.

Transport Pathways and Potential Source Regions of PM2.5 on the West Coast of Bohai Bay during 2009–2018

Mass concentration data for particulate matter with an aerodynamic diameter less than or equal to 2.50 μm (PM2.5) combined with backward trajectory cluster analysis, potential source contribution function (PSCF), and concentration weighted trajectory (CWT) methods were used to investigate the transport pathways and potential source regions of PM2.5 on the west coast of Bohai Bay from 2009 to 2018. Two pathways responsible for the transportation of high PM2.5 levels were identified, namely a southerly pathway and a northwesterly pathway. The southerly pathway represented the major transport pathway of PM2.5 for all seasons. As a regional transport pathway, it had the greatest impact in winter, followed by autumn. The southerly transport pathway passed over the Shandong and Hebei provinces before reaching Tianjin: Air masses were transported within the boundary layer (below 925 hPa), representing a slow-moving air flow. The northwesterly pathway mostly occurred in winter and autumn and passed over desert and semidesert regions in Outer Mongolia, the sand lands of Inner Mongolia, and Hebei. The air masses associated with the northwesterly pathway represented fast-moving airflows responsible for long-range transportation of PM2.5. Two potential source regions that contributed to high PM2.5 loadings on the west coast of Bohai Bay were identified, “southerly source regions” and “northwesterly source regions”. The southerly source regions, with weighted CWT (WCWT) values in winter greater than 140.00 μg/m3, were anthropogenic source regions, including southern Hebei, western Shandong, eastern Henan, northern Anhui, and northern Jiangsu. The northwesterly source regions, with WCWT values in winter of 80.00–140.00 μg/m3, were natural source regions, encompassing central Inner Mongolia and southern Mongolia. In addition, the southerly transport pathway passed though anthropogenic source regions, while the northwesterly transport pathway passed though natural source regions. The impacts of anthropogenic source regions on PM2.5 loadings on the west coast of Bohai Bay were greater than those of natural source regions.

The Ruthenium-106 plume over Europe in 2017: a source-receptor model to estimate the source region

Between the end of September and the beginning of October 2017, low but detectable air concentrations of Ruthenium-106 (R106u) were measured throughout the European atmosphere. To date, the source has not been clearly identified. This study aims at constraining the location of the most likely emission source, by combining HYSPLIT back trajectories and a multi-site source-receptor model. The model follows a concentration weighted trajectory (CWT) approach, based on a R106u measurement dataset gathered by the International Atomic Energy Agency (IAEA) shortly after the event and shared by the French Institut de Radioprotection et de Sûreté Nucléaire (IRSN). The back trajectories are computed using Global Data Assimilation System (GDAS) and ERA-Interim meteorological data, with horizontal resolution from 1.5° to 0.5°. The effect of the starting altitude was also investigated. The source-receptor model results show that the most likely emission source region extends from Ukraine to the West to the Russian Volga and Ural regions to the East, in accordance with two previous studies. The analyses also show that the identified source region is relatively insensitive to the type of meteorological data, their horizontal resolution and values of starting altitude. The model precision is found to increase with increasing number of receptors. The method is fully open-source, requires low computational resources and is therefore suited to estimate the source origin of radioactive pollutants on a real time basis, providing an additional tool to more sophisticated atmospheric models.

Evolution of the vertical structure of air pollutants during winter heavy pollution episodes: The role of regional transport and potential sources

Knowledge of vertical distribution of air pollutants is important for understanding the mechanisms underlying haze pollution. In this paper, we characterize the vertical structure of air pollutants based on ground-based Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) measurements in the wintertime in Hefei, East China. Both NO2 and aerosol show exponentially decreasing profile with high concentrations concentrated close to the surface, suggesting the major emissions are at ground level. SO2 profiles extend to slightly higher altitudes than NO2, which might be due to the SO2 emissions from elevated point sources (e.g., power plants). Elevated HCHO was observed in the middle layer during noon time, probably indicating that the larger effect of the photochemical formation of atmospheric HCHO rather than direct HCHO emissions. Potential source contribution function (PSCF) and concentration-weighted trajectory (CWT) models were used to evaluate the potential sources of Hefei's air pollution in the lower, middle and upper boundary layer. The results revealed that the major regional source of NO2 and aerosol were located in the northern and eastern part of Anhui and the transport mainly occured in the lower layer. Transported SO2 from the northwestern regions in the middle layer made great contribution to SO2 in Hefei. HCHO was mostly produced locally while the transport of HCHO from potential source areas was negligible. To further explore the potential source contributions affecting haze pollution, PSCF and CWT analysis for heavy haze episodes suggested that the potential source areas for aerosol were almost located in the northern region, the northwestern region, and the YRD region. Our findings provide a more comprehensive understanding for regional transport through the study on potential sources at different altitudes, which are useful for designing collaborative air pollution control strategies on a regional scale.

Regional sulfate drives long-term rise in AOD over megacity Kolkata, India

We present here the first long-term (2001–2017) record of aerosol optical depth (AOD; interchangeably, AOT) and contributions of aerosol chemical components to light extinction over Kolkata, the second-most polluted metropolis in India. For this purpose, we use daily gridded MODIS AOD measurements coupled with modeled AOT for 5 major aerosol constituents – sulfate, sea-salt, dust, organic carbon (OC) and black carbon (BC), from the MERRA-2 reanalysis system. We find that AOD over Kolkata has increased significantly (32% overall, 0.010 y−1; Mann-Kendall test with Thiel-Sen slope estimation; p < 0.01) over the past 17 y to a mean of 0.74 ± 0.10 in 2017, and an overwhelming majority of this increase is driven by a concurrent rise (70% overall, 0.007 y−1, p < 0.01) in sulfate AOT. This is followed by smaller but significant enhancements in OC (40% overall, 0.002 y−1, p < 0.01) and BC (20% overall, 0.0004 y−1, p < 0.01) AOT. Although a non-trivial fraction (24%) of AOT is associated with natural emissions (sea-salt and dust), these do not exhibit significant trends over time and therefore are not instrumental in driving the observed AOD rise. A concentration-weighted trajectory (CWT) analysis shows that sulfate aerosol over Kolkata is mostly regional (within ∼250 km) during winter and post-monsoon with significant footprints over thermal power plant clusters in neighboring states and areas with considerable residential biofuel use (eastern Indo-Gangetic Plain (IGP) and the Ganges-Brahmaputra Basin). In comparison, BC and OC AOT show a significant long-range component (∼1800 km) originating from northwestern and central IGP, especially during post-monsoon, when open agricultural residue burning is rampant. Overall, these results provide a preliminary indication that a considerable fraction of aerosol light extinction over Kolkata might be related to non-local, atmospherically transported aerosol. Once validated by ground-based measurements, these results would reinforce the need to bring regional and long-range emissions, in addition to within-the-city emissions, under the purview of air quality management policies.

Meteorological and chemical impacts on PM2.5 during a haze episode in a heavily polluted basin city of eastern China

Haze formation involves many interacting factors, such as secondary aerosol formation, unfavourable synoptic conditions and regional transport. The interaction between these factors complicates scientific understanding of the mechanism behind haze formation. In this study, we investigated the factors resulting in haze events in Longyou, a city located in a basin in China. Aerosol samples of PM2.5 were collected for subsequent chemical composition analysis between 11 January and 5 February 2018. The impacts of wind on PM2.5, SO2 and NO2 concentrations were analysed. Besides, the origin of air parcels and potential sources of PM2.5 were analysed by backward trajectory, potential source contribution function (PSCF) and concentration-weighted trajectories (CWT). Among the water-soluble ions identified, NO3− had the highest concentration, with further analysis demonstrating the haze evolution was mainly driven by the reactions involving NO3− formation. The dramatic increase of nitrate is mainly due to the homogeneous reaction of nitric acid with ammonia, while sulfate is likely due to heterogeneous reactions of NO2, SO2 and NH3. The average wind speed was less than 2 m/s during the aerosol sampling period, which could be considered as a stagnant state. Pollutants emitted by industrial area located in the northeast Longyou were probably brought to observation sites by continuous wind from northeast and accumulated gradually. Air parcels originating from the northeast of Zhejiang province also had large effects on haze pollution in Longyou. Together, our results showed that rapid secondary aerosol formation and unfavourable synoptic conditions are the main factors resulting in haze pollution in Longyou.

Influence of regional emissions on SO2 concentrations over Bhubaneswar, a capital city in eastern India downwind of the Indian SO2 hotspots

In a scenario when haze and smog events are wreaking havoc in many parts of the world, accurate information on ambient sulfur dioxide (SO2) sources is a required input to models for prediction and mitigation of air pollution. Globally, India is one of the highest emitters of anthropogenic SO2. However, the Ozone Monitoring Instrument (OMI) data reveal that unlike many other anthropogenic air pollutants, the strongest anthropogenic SO2 sources are not located in the Indo-Gangetic plain (IGP) but over the coal belts of North Eastern peninsular India. In this study, we report SO2 measurements conducted at Bhubaneswar, a rapidly developing smart city in the Eastern Coast of India. The city is ideally located just downwind of the Indian SO2 hotspots during winter, when SO2 concentrations are the highest, reaching 14.3 ppbv for hourly averaged data. The measurements, reported here from the summer of 2010 to the summer of 2012, show that despite being a rapidly developing location, SO2 over Bhubaneswar is dominated by regional emissions rather than local sources like vehicular exhausts. The influence of regional emissions is strongest in winter as the city is directly downwind of 6 of the 10 largest thermal power plants and 7 out of the 13 largest integrated steel plants in India with a mean SO2 concentration of 3.2 ppbv. This is evinced by multiple pointers viz. Concentration-Weighted Trajectory (CWT) analysis for surface SO2 data, correlation analysis for OMI SO2 data, analysis of surface concentrations of SO2, organic carbon, black carbon and carbon monoxide; which reveal SO2 emissions from the industrial and mining regions of Chhattisgarh and north-west Odisha. This is the same region that shows up as hotspots of SO2 in OMI retrievals over India. However, despite being downwind of major SO2 sources during winter, SO2 concentrations in Bhubaneswar are lower than over some other cities (Kolkata, Kanpur) in the IGP, due to influence of strong local sources in the later cases. Unlike most other urban regions in India, the diurnal variation of SO2 over Bhubaneswar shows elevated daytime values due to predominant influence of regional emissions.

Intra-regional transport of black carbon between the south edge of the North China Plain and central China during winter haze episodes

Abstract. Black carbon (BC), which is formed from the incomplete combustion of fuel sources (mainly fossil fuel, biofuel and open biomass burning), is a chemically inert optical absorber in the atmosphere. It has significant impacts on global climate, regional air quality and human health. During transportation, its physical and chemical characteristics as well as its sources change dramatically. To investigate the properties of BC (i.e., mass concentration, sources and optical properties) during intra-regional transport between the southern edge of the North China Plain (SE-NCP) and central China (CC), simultaneous BC observations were conducted in a megacity (Wuhan – WH) in CC, in three borderline cities (Xiangyang – XY, Suixian – SX and Hong'an – HA; from west to east) between the SE-NCP and CC, and in a city (Luohe – LH) in the SE-NCP during typical winter haze episodes. Using an Aethalometer, the highest equivalent BC (eBC) mass concentrations and the highest aerosol absorption coefficients (σabs) were found in LH in the SE-NCP, followed by the borderline cities (XY, SX and HA) and WH. The levels, sources, optical properties (i.e., σabs and absorption Ångström exponent, AAE) and geographic origins of eBC were different between clean and polluted periods. Compared with clean days, higher eBC levels (26.4 %–163 % higher) and σabs (18.2 %–236 % higher) were found during pollution episodes due to the increased combustion of fossil fuels (increased by 51.1 %–277 %), which was supported by the decreased AAE values (decreased by 7.40 %–12.7 %). The conditional bivariate probability function (CBPF) and concentration-weighted trajectory (CWT) results showed that the geographic origins of biomass burning (BCbb) and fossil fuel (BCff) combustion-derived BC were different. Air parcels from the south dominated for border sites during clean days, with contributions of 46.0 %–58.2 %, whereas trajectories from the northeast showed higher contributions (37.5 %–51.2 %) during pollution episodes. At the SE-NCP site (LH), transboundary influences from the south (CC) exhibited a more frequent impact (with air parcels from this direction comprising 47.8 % of all parcels) on the ambient eBC levels during pollution episodes. At WH, eBC was mainly from the northeast transport route throughout the observation period. Two transportation cases showed that the mass concentrations of eBC, BCff and σabs all increased, from upwind to downwind, whereas AAE decreased. This study highlights that intra-regional prevention and control for dominant sources at each specific site should be considered in order to improve the regional air quality.

Investigating daytime and night-time differences with the seasonal trend and sources of inorganic fine aerosols in Indo-Gangetic plain

This study investigates the seasonal distribution of inorganic aerosols in Central New Delhi and identifies their potential source regions using concentration weighted trajectories (CWTs). Secondary inorganic aerosols (\(\hbox {NO}_{3}^{-}\), \(\hbox {SO}_{4}^{2-}\), \(\hbox {NH}_{4}^{+})\) are the largest contributors to fine particulate matter in New Delhi, India. The concentrations of secondary inorganic aerosols showed very distinct seasonal patterns with higher concentrations in winter and post-monsoon seasons. Inorganic ions \(\hbox {Ca}^{2+}\), \(\hbox {Mg}^{2+}\) and \(\hbox {K}^{+}\) were also examined to understand their temporal trends. The primary aerosols were found to have smaller diurnal differences than secondary aerosols. The higher coefficient of divergence for secondary aerosols indicated a significant difference in their chemistry and/or meteorology during daytime and night-time, respectively. The backward trajectory analysis revealed the advection of ionic species from distant sources responsible for their significant seasonality. The highest concentrations of \(\hbox {K}^{+}\) during the post-monsoon season were mainly influenced by air masses arriving from Punjab and Haryana regions resulting from the prominent agricultural crop residue burning in these areas. CWT also identified the Thar Desert and Punjab as potential regions for enhanced levels of \(\hbox {Ca}^{2+}\) and \(\hbox {K}^{+}\), respectively. Also, the brick kilns located in western UP were observed as the major potential sources for \(\hbox {NO}_{3}^{-}\) and \(\hbox {SO}_{4}^{2-}\).

Summertime Aerosol over the West of Ireland Dominated by Secondary Aerosol during Long-Range Transport

The chemical composition and sources of non-refractory submicron aerosol (NR-PM1) on Galway, a west coast city of Ireland, were characterized using an aerosol chemical speciation monitor during summertime in June 2016. Organic aerosol (OA) was found to be the major part of NR-PM1 (54%), followed by secondary inorganic sulfate (25%), ammonium (11%), and nitrate (10%). Factor analysis revealed that oxygenated OA (OOA) was the dominant OA factor, on average accounting for 84% of the total OA. The remaining 16% of OA was attributed to primary peat burning associated with domestic heating activities. As a result, secondary organic and inorganic aerosol together accounted for 91% of the total NR-PM1, pointing to an aged aerosol population originating from secondary formation during long-range transport. Concentration-weighted trajectory analysis indicated that these secondary aerosols were mainly associated with easterly long-range transport from the UK and/or France.