Concentration Weighted Trajectory Analysis Research Articles

Transformation of Air Quality over a Coastal Tropical Station Chennai during COVID-19 Lockdown in India

To prevent the spread of COVID-19, Government of India imposed strict lockdown in the country from 24 March–31 May 2020, which allows the environment to revive with reduced emissions. The present work analyses the PM2.5, NO2, O3, CO and SO2 along with meteorological parameters (humidity, temperature and wind speed) at a tropical coastal station Chennai for March-May 2019 and 2020 at five locations: Alandur Bus depot, Velachery, Manali, Teynampet and U.S. Embassy Chennai. Chennai is a megacity of southern India and the state capital of Tamil Nadu, one of the worst affected states due to COVID-19. Though overall PM2.5 values decreased for the lockdown (ranging from ~32–187%), weekly analysis shows the variation in reduction/increase. SO2 and O3 values were found increasing for two sites: Teynampet (~40% in SO2 and ~48% in O3) and Velachery (~42% in SO2 and ~5% in O3), but decreasing for Alandur (~30% in SO2 and ~50% in O3) and Manali (~247% in SO2). NOx and CO were reduced during the lockdown (~47–125%) for all the sites. The source regions examined by concentration weighted trajectory analysis were found to change for transporting pollution to the site. The analysis shows there are local scale variations in the air pollution for the city during COVID-19 lockdown.

Effect of Lockdown due to COVID-19 on the Aerosol and Trace Gases Spatial Distribution over India and Adjoining Regions

Significant improvement in the air quality has been reported during the ‘Lockdown’ being implemented due to the Corona Virus Disease (COVID-19) pandemic in several parts of the globe. Using Ozone Monitoring Instrument (OMI) satellite measurements, we found a 50–60% reduction in the mean tropospheric columnar Nitrogen dioxide (NO2) and planetary boundary layer Sulphur dioxide (SO2) levels over India and adjoining regions during the lockdown (25 March–7 April 2020) compared to the pre-lockdown periods (8–21 March 2020). Similar decreases in aerosol concentrations over Indo-Gangetic Plain (IGP) and south India during lockdown are noticed in Moderate Resolution Imaging Spectroradiometer (MODIS) measurements, reaching the lowest values in the satellite era. Surprisingly, aerosol concentrations increased significantly (50–70%) during lockdown over central India when compared to pre-lockdown and climatology (2001–2019). A Concentration Weighted Trajectory analysis suggests that the air masses traveling from middle-east and Africa are the potential sources for the observed high aerosol concentrations over central India. Changes in the background meteorology (decrease in wind speed and increase in water vapour) during the lockdown made these aerosols stagnant and increased their size over central India, leading to higher AOD. These results suggest that natural sources (long-range transport) dominate anthropogenic pollution sources over India and adjoining regions, at least during the dry season. This finding is important to argue against the common belief that Asian countries are the main sources of pollution when long-range transport, which is a natural source, is the main cause. Lockdown has provided an opportunity to test this through a natural simulation by turning down the anthropogenic activities.

Isotopic composition of total gaseous mercury at a high-altitude tropical forest site influenced by air masses from the East Asia continent and the Pacific Ocean

Gaseous elemental mercury (GEM), gaseous oxidized mercury (GOM), particulate-bound mercury (PBM), and the isotopic composition of total gaseous mercury (TGM = GEM + GOM) were measured at the Lulin Atmospheric Background Station (LABS), a mountain background site downwind of the East Asia continent, from February 2015 to January 2016. Mean (±S.D.) concentrations of GEM, GOM, and PBM were 1.54 ± 0.34 ng m−3, 14.0 ± 27.8 pg m−3, and 2.6 ± 3.7 pg m−3, respectively. Concentration-Weighted Trajectory (CWT) analysis indicated that East and coastal China were the main source regions of elevated GEM observed at LABS. Weekly integrated TGM showed significant variations in δ202HgTGM (−0.42 to 0.41‰) and Δ199HgTGM (−0.31 to −0.13‰). Both δ202HgTGM and Δ199HgTGM showed clear seasonal variations, but the seasonal pattern of δ202HgTGM was different from that of Δ199HgTGM. The lowest mean δ202HgTGM was observed in spring (−0.15‰), while the lowest mean Δ199HgTGM was observed in summer (−0.24‰). A significant positive correlation (R2 = 0.38, p < 0.01) existed between δ202HgTGM and normalized difference vegetation index (NDVI), suggesting vegetation activity was an important factor controlling the seasonal variation of δ202HgTGM. In contrast, air mass transport path, which influences the source region of TGM to LABS, was likely the driver for the seasonal variations of Δ199HgTGM. Furthermore, results from the air mass classification showed distinguishable Δ199HgTGM signature for different air mass source regions, with air masses from South China Sea and western Pacific Ocean being characterized by more negative Δ199HgTGM (−0.25 ± 0.04‰). Results of this research demonstrated a clear difference in isotopic compositions of atmospheric Hg between continental and marine air masses.

Source Apportionment of Ambient Black Carbon During the COVID-19 Lockdown.

Black carbon (BC) particles being emitted from mobile and stationary emission sources as a result of combustion activities have significant impacts on human health and climate change. A lot of social activities have been halted during the COVID-19 lockdowns, which has evidently enhanced the ambient and indoor air quality. This paper investigates the possible emission sources and evaluates the meteorological conditions that may affect the dispersion and transport of BC locally and regionally. Ground-level equivalent BC (eBC) measurements were performed between January 2020 and July 2020 at a university campus located in Dammam city of the Kingdom of Saudi Arabia (KSA). The fossil fuel (eBCff) and biomass burning (eBCbb) fractions of total eBC (eBCt) concentrations were estimated as 84% and 16%, respectively, during the entire study period. The mean eBCbb, eBCff, and eBCt concentrations during the lockdown reduced by 14%, 24%, and 23%, respectively. The results of statistical analyses indicated that local fossil fuel burning emissions and atmospheric conditions apparently affected the observed eBC levels. Long-range potential source locations, including Iraq, Kuwait, Iran, distributed zones in the Arabian Gulf, and United Arab Emirates and regional source areas, such as the Arabian Gulf coastline of the KSA, Bahrain, and Qatar, were associated with moderate to high concentrations observed at the receptor site as a result of cluster analysis and concentration-weighted trajectory analysis methods.

Spatio-temporal variability of near-surface air pollutants at four distinct geographical locations in Andhra Pradesh State of India.

India is highly vulnerable to air pollution in the recent decade, especially urban areas with rapidly growing urbanisation and industrialisation. Here, we present spatio-temporal variability of air pollutants at four distinct locations in Andhra Pradesh State of India. The mean concentrations of air pollutants were generally higher at Visakhapatnam site than Amaravati, Rajahmundry, and Tirumala sites. The mean concentration of particulate matter of diameter less than 2.5μm (PM2.5) was higher at Visakhapatnam site (48.5±27.3μg/m3) by a factor of about 1.6 as compared to Tirumala site (29.5±17μg/m3). On the contrary, the mean concentrations of oxides of nitrogen (NOx, 70.3±28.1μg/m3) and ammonia (NH3, 20.5±9.2μg/m3) were higher at Tirumala by a factor of about 1.4 and 1.9, respectively, as compared to Visakhapatnam (49±5 μg/m3 and 10.7±5μg/m3). This was mainly attributed to higher vehicular emissions at Tirumala site. PM2.5, carbon monoxide (CO), NOx, and sulfur dioxide (SO2) showed distinct seasonal variation, with higher concentrations in winter followed by post-monsoon, pre-monsoon and monsoon. The Concentration Weighted Trajectory analysis of PM2.5 based on 5-days backward air mass trajectories showed that all sites experienced northeast air mass flow indicative of the outflow from Indo-Gangetic Plain, particularly in the post-monsoon and winter seasons. The Continuous Wavelet Transform analysis further showed that higher variations in PM2.5 concentrations occurring at a regular interval from a week to 16 days at both Tirumala and Visakhapatnam sites, while weekly periods are dominant over Amaravati and Rajahmundry sites with 95% significance during post-monsoon and winter seasons. Overall, our results underline heterogeneity in air pollution emission sources and influx of pollutants from distant sources, which would be useful when formulating the policies and mitigation procedures for this region.

Distribution of atmospheric gaseous elemental mercury (Hg(0)) from the Sea of Japan to the Arctic, and Hg(0) evasion fluxes in the Eastern Arctic Seas: Results from a joint Russian-Chinese cruise in fall 2018

The Eastern Arctic Seas and the north-western Pacific are among the most poorly investigated areas as far as Hg cycling in marine systems is concerned. Continuous measurements of gaseous elemental mercury (Hg(0)) concentrations in the marine boundary layer and Hg(0) evasion fluxes from the sea surface were performed in these regions in fall 2018. Atmospheric Hg(0) concentrations of 1.02–2.50 ng/m3 were measured (average: 1.45 ± 0.12 ng/m3; N = 2518). Values in the Far Eastern Seas of Russia were lower compared to previous observations, presumably reflecting а global trend of decreasing atmospheric Hg(0). Concentration-weighted trajectory analysis highlighted three source regions influencing Hg(0) concentrations in the ambient air during the cruise: 1) the north-eastern China and the Yellow Sea region; 2) the Kuril-Kamchatka region of the Pacific Ocean and the region around the Commander and Aleutian Islands; and 3) the Arctic region. In the Arctic, sea-air Hg(0) evasion fluxes were at the same low levels as those observed earlier in the northern sea areas (0.28–1.35 ng/m2/h, average, 0.70 ± 0.26 ng/m2/h, N = 29). In the Eastern Arctic Seas, Hg(0) evasion fluxes were significantly dependent on river runoff. In the Arctic Ocean, they were negatively correlated with water temperature and positively correlated with salinity, suggesting a proximity to areas with contiguous ice and higher dissolved Hg(0) concentrations in the surface seawater. These findings are consistent with the hypothesis that the Arctic Ocean is a source of atmospheric Hg(0) during late summer and fall.

Long-term (2008–2017) analysis of atmospheric composite aerosol and black carbon radiative forcing over a semi-arid region in southern India: Model results and ground measurement

To achieve an in-depth understanding of radiative forcing due to aerosols is a crucial challenge for climate change studies. The first-ever long-term measurement of direct shortwave composite and black carbon aerosol radiative properties over a semi-arid region, Anantapur, in southern India is presented. Long-term variations in Aerosol Optical Depth (AOD) and Black Carbon (BC) mass concentration from December 2007 to November 2017 are discussed with specific emphasis on intra-seasonal variation in aerosol optical properties, meteorology, transport pathways, and their implications for direct short wave radiative forcing over Anantapur. The intra-seasonal mean AOD showed strong seasonal dependence with the highest (0.47 ± 0.03) during summer and lowest (0.28 ± 0.03) during the monsoon. Meanwhile, the intra-seasonal mean (±σ) BC mass concentration was about 3.57 ± 0.45, 2.60 ± 0.58, 1.22 ± 0.18 and 2.24 ± 0.28 μg m−3 during winter, summer, monsoon and post-monsoon respectively. Furthermore, there is an obvious temporal variation in intra-seasonal BC mass concentration during the dry season (winter and summer). To be more specific, the intra-seasonal mean (±σ) BC mass concentration before 2012 (after 2012) during the dry season was about 3.37 ± 0.7 μg m−3 (2.80 ± 0.58 μg m−3), respectively. Concentration weighted trajectory analyses (CWT) revealed that the air masses originated from the continental and polluted environments located in the central and northern parts of India (except monsoon), in regulating BC mass concentration over measurement location. Further, Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) derived aerosol vertical extinction profiles (532 nm) showed that majority aerosols (>250 Mm−1) are confined within 2 km from the surface during winter while in summer particles are distributed throughout the profile (~6 km) with extinction coefficient varying between 200 and 250 Mm−1. The Santa Barbara Discrete Ordinate Radiative Transfer (SBDART) model estimated intra-seasonal mean direct shortwave composite aerosol radiative forcing (DARF) in the atmosphere (ATM) was about 31.13 ± 3.36, 34.82 ± 3.89, 17.10 ± 1.15, and 17.44 ± 1.81 Wm-2 during winter, summer, monsoon and post-monsoon, respectively. The positive signs of ATM forcing in all seasons indicate a warming of the atmosphere, and the corresponding heating rate was around a factor of two higher during the dry season (0.92 ± 0.12 Kday−1) than the wet season (monsoon and post-monsoon) (0.49 ± 0.04 Kday−1). The intra-seasonal mean BC forcing in ATM before 2012 (After 2012) during the dry season was about 24.14 ± 2.85Wm-2(20.09 ± 2.59Wm-2), respectively. The contribution of BC alone to the composite forcing during the study period over the station was ~68%. These findings would be helpful for regional climate studies and making air pollution control policy over the region.

Black Carbon: The Concentration and Sources Study at the Nam Co Lake, the Tibetan Plateau from 2015 to 2016

We measured black carbon (BC) with a seven-wavelength aethalometer (AE-31) at the Nam Co Lake (NCL), the hinterland of the Tibetan Plateau (TP) from May 2015 to April 2016. The daily average concentration of BC was 145 ± 85 ng m−3, increasing by 50% since 2006. The seasonal variation of BC shows higher concentrations in spring and summer and lower concentrations in autumn and winter, dominated by the adjacent sources and meteorological conditions. The diurnal variation of BC showed that its concentrations peaked at 9:00–16:00 (UTC + 8), significantly related to local human activities (e.g., animal-manure burning and nearby traffic due to the tourism industry). The concentration-weighted trajectory (CWT) analysis showed that the long-distance transport of BC from South Asia could also be a potential contributor to BC at the NCL, as well as the biomass burning by the surrounding residents. The analyses of the absorption coefficient and absorption Ångström exponent show the consistency of sourcing the BC at the NCL. We suggest here that urgent measures should be taken to protect the atmospheric environment at the NCL, considering the fast-increasing concentrations of BC as an indicator of fuel combustion.

Latest observations of total gaseous mercury in a megacity (Lanzhou) in northwest China

One year of online total gaseous mercury (TGM) measurements were carried out for the first time in Lanzhou, a city in northwest China that was once seriously polluted. Measurements were made from October 2016 to October 2017 using the Tekran 2537B instrument, and the annual mean concentration of TGM in Lanzhou was 4.48 ± 2.32 ng m−3 (mean ± standard deviation). TGM concentrations decreased during the measurement period, with autumn 2017 average concentrations 2.87 ng m−3 lower than autumn 2016 average concentrations. Similar diurnal variations of TGM were obtained in different seasons with low concentrations observed in the afternoon and high concentrations at night. The principal component analysis and conditional probability function results revealed that the sources of mercury were similar to the other atmospheric pollutants such as SO2, CO, NO2 and PM2.5, and were mainly from industrial combustion plants in urban districts. Concentration weighted trajectory analysis using backward trajectories demonstrated that higher mercury concentrations were related to air masses from adjacent regions, indicating the importance of influences from local-to-regional scale sources. A synthesis of multi-decadal atmospheric mercury measurements in Lanzhou and other Chinese megacities revealed that atmospheric mercury concentrations were either generally stable or experienced a slight decrease, during a time when China implemented control measures on atmospheric pollution. Long-term atmospheric mercury observations in urban and background sites in China are warranted to assess mercury pollution and the effectiveness of China's mercury control policies.

Source Identification of Trace Elements in PM2.5 at a Rural Site in the North China Plain

An intensive sampling of PM2.5 was conducted at a rural site (Gucheng) in the North China Plain from 22 October to 23 November 2016. A total of 25 elements (Al, Na, Cl, Mg, P, S, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Br, Sr, Cd, Ba, Pb, and Sb) from PM2.5 filter samples collected daily were measured using a wavelength dispersive X-ray fluorescence spectrometer. Cl, S, and K were the most abundant elements, with average concentrations of 2077.66 ng m−3 (range 118.88–4638.96 ng m−3), 1748.78 ng m−3 (range 276.67–4335.59 ng m−3), and 1287.07 ng m−3 (range 254.90–2748.63 ng m−3), respectively. Among noncrustal trace metal elements, the concentration of Zn was the highest, with an average of 397.74 ng m−3 (range 36.45–1602.96 ng m−3), followed by Sb and Pb, on average, of 299.20 ng m−3 and 184.52 ng m−3, respectively. The morphologies of PM2.5 samples were observed using scanning electron microscopy. The shape of the particles was predominantly spherical, chain-like, and irregular. Positive matrix factorization analysis revealed that soil dust, following by industry, secondary formation, vehicle emissions, biomass and waste burning, and coal combustion, were the main sources of PM2.5. The results of cluster, potential source contribution function, and concentration weighted trajectory analyses suggested that local emissions from Hebei Province, as well as regional transport from Beijing, Tianjin, Shandong, and Shanxi Province, and long-range transport from Inner Mongolia, were the main contributors to PM2.5 pollution.

Seasonal Variation of OC, EC, and WSOC of PM10 and Their CWT Analysis Over the Eastern Himalaya

In the present study, seasonal transport trends and potential source regions of carbonaceous species [organic carbon (OC), elemental carbon (EC), water-soluble organic carbon (WSOC), secondary organic carbon (SOC) and total carbonaceous aerosols (TCAs)] of PM10 was evaluated over Darjeeling, an eastern Himalayas of India during August 2018–June 2019. Backward trajectories, cluster analysis, and concentration-weighted trajectory (CWT) analysis were performed to evaluate the seasonal transport pathway of carbonaceous aerosols over the region. The annual average concentration of PM10 was recorded to be 55 ± 18 μg m−3, which is close to National Ambient Air Quality Standard (NAAQS; 60 μg m−3 for annual PM10) of India. The concentration of PM10 showed maxima in pre-monsoon season (63 ± 21 μg m−3) followed by post-monsoon (56 ± 16 μg m−3), monsoon (51 ± 13 μg m−3) and winter seasons (49 ± 17 μg m−3). The study revealed that the WSOC comprises about 72% of OC concentration with maxima in post-monsoon (81% of OC) followed by winter (74% of OC), pre-monsoon (67% of OC) and monsoon seasons (66% of OC). The concentration of SOC were estimated as 1.4 ± 0.9, 1.7 ± 1.0, 2.4 ± 0.9 and 1.9 ± 0.9 µg m−3 during pre-monsoon, monsoon, post-monsoon and winter, respectively (which are accounted for 27%, 49%, 41% and 35% to the OC mass concentration, respectively). The results indicated that biomass burning could be one of the major sources of carbonaceous aerosols in Darjeeling. Five days backward trajectory analysis (including cluster and CWT analysis) revealed that the air-mass flow of pollutants towards the sampling site of Darjeeling majorly coming from continental sites (Nepal and Indo-Gangetic plain (IGP) region of India) and the Bay of Bengal (BOB).

Multichannel characteristics of absorbing aerosols in Xuzhou and implication of black carbon

Black carbon (BC) is an important component of atmospheric aerosols; BC aerosols are produced mainly by the incomplete combustion of carbon-containing substances, and they have important effects on climate change, the atmospheric environment, and public health. Most of the existing research has focused on the single-band measurement results of BC aerosols. However, each band offers different information regarding the optical absorption properties of aerosols, such as enhanced light absorption by brown carbon in the 370 nm band. To bridge this research gap, the present study used BC concentration data measured by an AE42 aethalometer to analyze the multiband pollution characteristics of BC aerosols in Xuzhou city in China. An aethalometer model was established to quantitatively describe the concentrations of BC produced by solid and liquid fuels, and a concentration-weighted trajectory analysis was used to analyze the potential sources of BC aerosols in Xuzhou and their contributions to the total BC. The following results were obtained. (1) The BC concentration was high in spring and winter and low in summer and autumn, and the diurnal variation showed bimodal characteristics. (2) The difference among the aerosol concentrations in the seven bands was larger in autumn and winter than in spring and summer, and the contribution of brown carbon in autumn and winter was greater than that in spring and summer. (3) In winter, the solid source (coal and biomass combustion) of BC accounted for a large proportion of the total BC. (4) A source analysis of BC pollution days and BC clean days indicated different sources of BC pollution in different seasons. The results of this study provide a theoretical basis and realistic guide for the prevention and control of atmospheric pollution in Xuzhou and are anticipated to be of great significance for improving the regional and global atmospheric environment.

Large-scale particulate air pollution and chemical fingerprint of volcanic sulfate aerosols from the 2014–2015 Holuhraun flood lava eruption of Bárðarbunga volcano (Iceland)

Abstract. Volcanic sulfate aerosols play a key role in air quality and climate. However, the rate of oxidation of sulfur dioxide (SO2) precursor gas to sulfate aerosols (SO42-) in volcanic plumes is poorly known, especially in the troposphere. Here we determine the chemical speciation as well as the intensity and temporal persistence of the impact on air quality of sulfate aerosols from the 2014–2015 Holuhraun flood lava eruption of Icelandic volcano Bárðarbunga. To do so, we jointly analyse a set of SO2 observations from satellite (OMPS and IASI) and ground-level measurements from air quality monitoring stations together with high temporal resolution mass spectrometry measurements of an Aerosol Chemical Speciation Monitor (ACSM) performed far from the volcanic source. We explore month/year long ACSM data in France from stations in contrasting environments, close and far from industrial sulfur-rich activities. We demonstrate that volcanic sulfate aerosols exhibit a distinct chemical signature in urban/rural conditions, with NO3:SO4 mass concentration ratios lower than for non-volcanic background aerosols. These results are supported by thermodynamic simulations of aerosol composition, using the ISORROPIA II model, which show that ammonium sulfate aerosols are preferentially formed at a high concentration of sulfate, leading to a decrease in the production of particulate ammonium nitrate. Such a chemical signature is however more difficult to identify at heavily polluted industrial sites due to a high level of background noise in sulfur. Nevertheless, aged volcanic sulfates can be distinguished from freshly emitted industrial sulfates according to their contrasting degree of anion neutralization. Combining AERONET (AErosol RObotic NETwork) sunphotometric data with ACSM observations, we also show a long persistence over weeks of pollution in volcanic sulfate aerosols, while SO2 pollution disappears in a few days at most. Finally, gathering 6-month long datasets from 27 sulfur monitoring stations of the EMEP (European Monitoring and Evaluation Programme) network allows us to demonstrate a much broader large-scale European pollution, in both SO2 and SO4, associated with the Holuhraun eruption, from Scandinavia to France. While widespread SO2 anomalies, with ground-level mass concentrations far exceeding background values, almost entirely result from the volcanic source, the origin of sulfate aerosols is more complex. Using a multi-site concentration-weighted trajectory analysis, emissions from the Holuhraun eruption are shown to be one of the main sources of SO4 at all EMEP sites across Europe and can be distinguished from anthropogenic emissions from eastern Europe but also from Great Britain. A wide variability in SO2:SO4 mass concentration ratios, ranging from 0.8 to 8.0, is shown at several stations geographically dispersed at thousands of kilometres from the eruption site. Despite this apparent spatial complexity, we demonstrate that these mass oxidation ratios can be explained by a simple linear dependency on the age of the plume, with a SO2-to-SO4 oxidation rate of 0.23 h−1. Most current studies generally focus on SO2, an unambiguous and more readily measured marker of the volcanic plume. However, the long persistence of the chemical fingerprint of volcanic sulfate aerosols at continental scale, as shown for the Holuhraun eruption here, casts light on the impact of tropospheric eruptions and passive degassing activities on air quality, health, atmospheric chemistry and climate.

Hybrid multiple-site mass closure and source apportionment of PM2.5 and aerosol acidity at major cities in the Po Valley

This study investigates the major chemical components, particle-bound water content, acidity (pH), and major potential sources of PM2.5 in major cities (Belluno, Conegliano, Vicenza, Mestre, Padua, and Rovigo) in the eastern end of the Po Valley. The measured PM2.5 mass was reconstructed using a multiple-site hybrid chemical mass closure approach that also accounts for aerosol inorganic water content (AWC) estimated by the ISORROPIA-II model. Annually, organic matter accounted for 31–45% of the PM2.5 at all sites, followed by nitrate (10–19%), crustal material (10–14%), sulfate (8–10%), ammonium (5–9%), elemental carbon (4–7%), other inorganic ions (3–4%), and trace elements (0.2–0.3%). Water represented 7–10% of measured PM2.5. The ambient aerosol pH varied from 1.5 to 4.5 with lower values in summer (average in all sites 2.2 ± 0.3) and higher in winter (3.9 ± 0.3). Six major PM2.5 sources were quantitatively identified with multiple-site positive matrix factorization: secondary sulfate (34% of PM2.5), secondary nitrate (30%), biomass burning (17%), traffic (11%), re-suspended dust (5%), and fossil fuel combustion (3%). Biomass burning accounted for ~90% of total PAHs. Inorganic aerosol acidity was driven primarily by secondary sulfate, fossil fuel combustion (decreasing pH), secondary nitrate, and biomass burning (increasing pH). Secondary nitrate was the primary driver of the inorganic AWC variability. A concentration-weighted trajectory (multiple-site) analysis was used to identify potential source areas for the various factors and modeled aerosol acidity. Eastern and Central Europe were the main source areas of secondary species. Less acidic aerosol was associated with air masses originating from Northern Europe owing to the elevated presence of the nitrate factor. More acidic particles were observed for air masses traversing the Po Valley and the Mediterranean, possibly due to the higher contributions of fossil fuel combustion factor and the loss of nitric acid due to its interaction with coarse sea-salt particles.

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.

Black carbon in Xiamen, China: Temporal variations, transport pathways and impacts of synoptic circulation.

Black carbon (BC) plays a vital role in atmospheric environment and climate change. Temporal variations and transport pathways of BC in Xiamen, China with the impacts of synoptic circulation were investigated in 2014 with Aethalometer. Annual mean BC concentration was 4270 ng m-3. BC exhibited clear diurnal (seasonal) variations, with the maximum of 6182 (4755) ng m-3 at 6:00 (in spring) and minimum of 2847 (3774) ng m-3 at 13:00 (in summer). Conditional probability function analysis indicated that high BC concentrations were associated with northwesterly winds with low wind speed. Air masses originating from the East China Sea and passing along with East China Coast had the highest BC concentrations. Potential source contribution function and concentration weighted trajectory analysis suggested that major sources for BC included the surrounding region, southwestern Fujian and eastern Guangdong to the southwest, Hubei, Hunan and Jiangxi to the northwest, the East China Sea and the South China Sea. Of the nine synoptic circulation patterns, three cyclone-related patterns were associated with low BC concentrations and small biomass burning (BCbb) contributions. Of the six anticyclone-related patterns, the three cold-high circulations around winter were associated with moderate BC concentrations and large BCbb contributions. The two cold-high patterns in spring and autumn were associated with high BC concentrations and small BCbb contributions, while the warm-high pattern was associated with moderate BC concentration and small BCbb contribution. The findings provide insights into the transport mechanisms of BC with the impacts of synoptic pattern in China.

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.

Characteristics and sources of carbonaceous aerosol across urban and rural sites in a rapidly urbanized but low-level industrialized city in the Sichuan Basin, China.

Organic carbon (OC) and elemental carbon (EC) were measured in 24h fine particulate matter (PM2.5) samples collected from May 2015 to April 2016 at urban and rural sites in Nanchong, a rapidly urbanized but low-level industrialized city in the Sichuan Basin, China. The annual average PM2.5, OC, and EC concentrations at urban sites were 45.6-55.7, 8.5-11.5, and 2.8-3.4μgm-3, respectively, which were similar to the corresponding values (48.3, 10.6, and 3.3μgm-3) at the rural site. The PM2.5 concentrations displayed strong monthly variations, with the highest (78.8-105.0μgm-3) in January or February. Likewise, daily OC and EC concentrations exhibited high values in October (only for OC) and December 2015 to February 2016. Correlation, positive matrix factorization, and concentration weighted trajectory analyses were combined to investigate the sources of carbonaceous aerosol. The results indicated that OC and EC were mainly from biomass burning (60.7% and 45.8%) and coal combustion (30.2% and 25.7%), followed by vehicle emissions and road dust. The enhanced emissions from residential coal and biofuel uses in winter and straw combustion in October contributed to higher concentrations of OC and EC during these months. The contributions of biomass burning to OC and EC were significantly higher at the rural site (69.2% and 51.8%) than urban sites (56.3-58.6% and 37.8-41.5%). In addition to local emissions, the high concentrations of OC and EC at Nanchong were also influenced by regional transport in the basin.

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.

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.