Sources, transport, and visibility impact of ambient submicrometer particle number size distributions in an urban area of central Taiwan

This study applied positive matrix factorization (PMF) to identify the sources of size-resolved submicrometer (10-1000 nm) particles and quantify their contributions to impaired visibility based on the particle number size distributions (PNSDs), aerosol light extinction (b_p), air pollutants (PM₁₀, PM_2.5, SO₂, O₃, and NO), and meteorological parameters (temperature, relative humidity, wind speed, wind direction, and ultraviolet index) measured hourly over an urban basin in central Taiwan between 2017 and 2021. The transport of source-specific PNSDs was evaluated with wind and back trajectory analyses. The PMF revealed six sources to the total particle number (TPN), surface (TPS), volume (TPV), and b_p. Factor 1 (F1), the key contributor to TPN (35.0 %), represented nucleation (<25 nm) particles associated with fresh traffic emission and secondary new particle formation, which were transported from the west-southwest by stronger winds (>2.2 m s^-1). F2 represented the large Aitken (50-100 nm) particles transported regionally via northerly winds, whereas F3 represented large accumulation (300-1000 nm) particles, which showed elevated concentrations under stagnant conditions (<1.1 m s^-1). F4 represented small Aitken (25-50 nm) particles arising from the growth and transport of the nucleation particles (F1) via west-southwesterly winds. F5 represented large Aitken particles originating from combustion-related SO₂ sources and carried by west-northwesterly winds. F6 represented small accumulation (100-300 nm) particles emitted both by local sources and by the remote SO₂ sources found for F5. Overall, large accumulation particles (F3) played the greatest role in determining the TPV (66.4 %) and TPS (34.8 %), and their contribution to b_p increased markedly from 17.3 % to 40.7 % as visibility decreased, indicating that TPV and TPS are better metrics than TPN for estimating b_p. Furthermore, slow-moving air masses-and therefore stagnant conditions-facilitate the build-up of accumulation mode particles (F3 + F6), resulting in the poorest visibility.

Short-chain chlorinated paraffins in soils indicate landfills as local sources in the Tibetan Plateau

Background contamination levels of contemporary persistent organic pollutants (POPs) may be elevated due to local discharges, and hence it is of high importance to assess and monitor them in alpine and Polar Regions. This study investigated the role of waste disposal in the Tibetan plateau as the local source of short-chain chlorinated paraffins (SCCPs). SCCPs were determined in soils from the urban landfill and rural dumpsites, with a concentration range of 56.8-1348 ng/g dw. The gradient descent of SCCP levels from Lhasa landfill to the surrounding soils with increasing distances suggested a significant SCCP release from waste disposal. The transport pattern was well fitted by the Boltzmann equation after normalization in terms of soil organic carbon contents. Compared to the landfill cells closed in early years, the recently closed cells contained higher concentrations but lower proportions of the short-chain congener groups, likely reflecting the SCCP use history in Tibet. In open-burning dumpsites, higher SCCP levels and dominance of lighter congener groups indicates that such crude waste treatment process might cause an extra release of volatile SCCPs. This study elucidates local SCCP inputs to the background environment, and demonstrates that both urbanization and badly-managed landfill have been contributing to the presence of contemporary POPs in the Tibetan Plateau.

Black carbon in a glacier and snow cover on the northeastern Tibetan Plateau: Concentrations, radiative forcing and potential source from local topsoil

Black carbon (BC), which consists of the strongest light-absorbing particles (LAP) in snow/ice, has been regarded as a potential factor accelerating the melting of glaciers and snow cover over the Third Pole. During the winter and summer of 2016, snow, ice and topsoil were sampled from the Laohugou basin located on the northeastern Tibetan Plateau. Concentrations of BC in Laohugou Glacier No. 12 (LG12) and snow cover in this basin (LSC) varied broadly (21.7-2700.1 and 89.6 to 6326.2 ng g^-1, respectively), indicating large spatiotemporal variability in wet, dry and post depositional conditions. Further, internally mixed BC in snow grains enhanced the albedo reduction (15.0-26.3%) more than externally mixed BC in LG12 and LSC. Dust played a more important role than BC in accelerating the melting of LG12, whereas these components played comparable roles in accelerating the melting of LSC. In total, externally mixed BC and dust reduced the albedo by 0.075-0.423, with an associated mean radiative forcing (RF) of 97.5 ± 41.5 Wm^-2 in LSC. This level was lower than those in the ablation zone (354.1 ± 81.2 Wm^-2) and accumulation zone (145.6 ± 76.7 Wm^-2) of LG12 because of discrepancies in LAP concentrations, solar zenith angles and incoming shortwave radiation. Furthermore, we observed that topsoil containing abundant BC was transported along the slope from the debris to the LG12 surface ice, and topsoil in this region could be lifted by strong mountain-valley winds and then deposited on snow/ice surfaces, which affected the LAP concentrations. Therefore, this study is important for understanding the role of BC and dust in the melting of snow/ice in the northeastern Tibetan Plateau.

Geochemical baseline establishment and pollution source determination of heavy metals in lake sediments: A case study in Lihu Lake, China

Geochemical baseline, as the boundary between background and anomalous values of pollutants in sediments, is typically used to evaluate whether sediments are disturbed by human activities. However, this tool is rarely used in identifying the pollution source types of heavy metals. This study aims to determine the pollution source of heavy metals in sediments based on the geochemical baseline by using statistical methods. The geochemical baseline values of surface and core sediments in Lihu Lake, a typical urban lake in Taihu Lake Basin, were calculated by relative cumulative frequency and iterative methods. The enrichment degree and pollution source of heavy metals in surface sediments were also determined. The metal baselines in the core or surface sediments calculated by the two methods did not show significant difference (P > 0.05). The geochemical baseline of core sediments could represent the background level of sediments in the study area. The enrichment extent of the tested metals in surface sediments followed the order of: Pb > Zn > Hg > As > Cu > Cd > Ni > Cr. The average contents of Pb and Zn were 3.0 and 2.1 times of the background values, and their pollution were mainly derived from local and non-point sources, respectively. The contributions of the background concentrations to the contents of Cu, As, and Hg were slightly higher than that of human interference, and accounted for 59.4%, 58.4%, and 54.0% of the total contents, respectively. The pollutions of Cu and As mainly originated from non-point source, and that of Hg was mainly derived from local source. The contents of Cr, Ni, and Cd were within the background level. Geochemical baseline can be used not only to determine the enrichment degree but also as a potentially useful tool for identifying the pollution source (local and non-point source) of heavy metals in sediments.

Occurrences, sources, and transport of hydrophobic organic contaminants in the waters of Fildes Peninsula, Antarctica

As a pristine continent, Antarctica provides a good opportunity to study the spatial transport and temporal accumulation of environmental contaminants and the impacts of anthropogenic activities, both of which have given rise to ongoing public concern. In this research, an approach of coupling aquatic time-integrated passive sampling with chemical analysis and bioassays was used to assess pollution by hydrophobic organic contaminants in Antarctic waters. Passive samplers were deployed in waters of Fildes Peninsula, Antarctica, and their extracts were used for chemical analyses of sixty-six hydrophobic organic contaminants belonging to five groups [organophosphorus flame retardants (PFRs), phthalic acid esters (PAEs), polycyclic aromatic hydrocarbons (PAHs), organochlorine pesticides (OCPs), and polychlorinated biphenyls (PCBs)] and in vitro bioassays for endocrine disruption and genotoxicity. In total, twenty pollutants (six PFRs, one PAE, two PAHs, six OCPs, and five PCBs) were quantified, and six PFRs had concentrations that ranged from ND (not detected) to 44.37 ng L^-1 in Antarctic waters. The concentrations detected in the waters were generally low and insufficient to have significant in vitro endocrine disruption potential or genotoxicity. The source and transport pathways of PFRs and PAE in Fildes Peninsula were studied, and multiple local sources (wastewater, air traffic, research stations, and animal feces) for different PFRs were proposed. A spatial and temporal analysis showed slight changes in the exposure of OCPs and PCBs in Antarctic waters. Furthermore, a comparison among a variety of Antarctic water sampling cases revealed that passive sampling can be a tool for aquatic time-integrated investigations in polar regions.

Snowpack deposition of trace elements in the Athabasca oil sands region, Canada

The total recoverable and dissolved concentrations of 29 metals and metalloids were analyzed in snowpack collected at 91 sites in the Athabasca oil sands region, Canada in winter 2011. Based on deposition pattern from geographical centre, three groups were found: Type-1 metals (i.e. dissolved and total recoverable V; Mo) showed a significant exponential decrease with distance, suggesting oil sands development sources; Type-2 elements (e.g. Al, Sb, As, Ba, Fe, Ni, Tl, and Ti and Zn) showed exponentially decline patterns but with some local point sources; Type-3 elements (e.g. Cd, Cl, Cr, Mn, Sr and Th) deposition pattern represented local sources. A self-organizing map showed that sites with the highest elemental concentrations (Cluster I) were mainly located in the vicinity of upgrading facilities and along the north-south transects. The lowest elemental concentration sites (Cluster III) were the most distal sites or located in the western region of the study area.