Sensitivity of fine particulate matter concentrations in South Korea to regional ammonia emissions in Northeast Asia

Ammonia (NH3) is an important precursor for forming PM2.5. In this study, we estimated the impact of upwind transboundary and local downwind NH3 emissions on PM2.5 and its inorganic components via photochemical grid model simulations. Nine sensitivity scenarios with ±50% perturbations of upwind (China) and/or downwind (South Korea) NH3 emissions were simulated for the year 2016 over Northeast Asia. The annual mean PM2.5 concentrations in the downwind area were predicted to change from -3.3 (-18%) to 2.4 μg/m3(13%) when the NH3 emissions in the upwind and downwind areas were perturbed by -50% to +50%. The change in PM2.5 concentrations in the downwind area depending on the change in NH3 emissions in the upwind area was the highest in spring, followed by winter. This was mainly attributed to the change in nitrate (NO3-), a secondary inorganic aerosol (SIA) that is a predominant constituent of PM2.5. Since NH3 is mainly emitted near the surface and vertical mixing is limited during the night, it was modeled that the aloft nitric acid (HNO3)-to-NO3- conversion in the morning hours was increased when the NH3 accumulated near the surface during nighttime begins to mix up within the Planetary Boundary Layer (PBL) as it develops after sunrise. This implies that the control of upwind and/or downwind NH3 emissions is effective at reducing PM2.5 concentrations in the downwind area even under NH3 rich conditions in Northeast Asia.

Direct and cross impacts of upwind emission control on downwind PM2.5 under various NH3 conditions in Northeast Asia

Emissions reductions in upwind areas can influence the PM_2.5 concentrations in downwind areas via long-range transport. However, few studies have assessed the impact of upwind PM_2.5 precursor controls on changes in downwind PM_2.5 concentrations. In this study, we analyzed the overall impact of PM_2.5 precursor emission controls in upwind areas on PM_2.5 in downwind areas with two types of impacts: "direct impact" and "cross impact." The former refers to PM_2.5 changes in downwind areas due to the transported PM_2.5 itself, whereas the latter represents PM_2.5 changes due to reactions between the transported gaseous precursors and intermediates (i.e., HNO₃) originating from upwind areas and locally emitted precursors (i.e. NH₃) in the downwind areas. As a case study, we performed air quality modeling for Northeast Asia for January 15-17, 2016 by setting China and South Korea as the upwind and downwind areas, respectively. To account for potential spatiotemporal variations in NH₃ emissions in downwind areas, we considered two NH₃ conditions. When NOx emissions in China were reduced by 35%, in downwind areas the PM_2.5 concentrations decreased by 2.2 μg/m³ under NH₃-rich conditions, while PM_2.5 concentrations increased by 2.3 μg/m³ under NH₃-poor conditions. The direct impact increased by 4.0 μg/m³ in both cases due to upwind NO_x disbenefit effects. However, the cross impacts led to a PM_2.5 decrease of 6.2 μg/m³ under NH₃-rich conditions versus a PM_2.5 increase of 1.7 μg/m³ under NH₃-poor conditions. We noted that PM_2.5 concentrations in the downwind areas may not improve unless a cross impact outweighs a direct impact. This may be one of the reasons why South Korea PM_2.5 concentrations have not declined despite efforts by China to reduce their PM_2.5 precursor emissions.

Impacts of local versus long-range transported aerosols on PM10 concentrations in Seoul, Korea: An estimate based on 11-year PM10 and lidar observations

Extreme haze episodes have frequently occurred in Seoul since mid-2010s by the combined contributions of transboundary transported aerosols as well as locally emitted pollutants. In this study, we developed a novel method to estimate the contribution of long-range transport (LRT, aerosols are transported from any regions except local area near Seoul) and local pollution (LP, aerosols are originated from local area near Seoul) cases to the PM₁₀ concentration in Seoul, Korea, using the PM₁₀ concentration ratio between surface (PM₁₀^S) and mountaintop (PM₁₀^M) sites and the lidar-derived mixing layer height. The overall contributions of LRT and LP events to nighttime high-PM₁₀ episodes (PM₁₀ > 50 μg m^-3) during the period of May 2008-April 2019 were estimated to be approximately 32% and 47%, respectively. The monthly contribution of LRT events to the PM₁₀ concentration varied from approximately 18% (July) to 43% (January), whereas the contribution of LP events was estimated between 39% (March) and 69% (July); this pattern was associated with seasonal synoptic circulations. The similar PM₁₀^S values between the LRT (71 ± 22 μg m^-3) and LP (73 ± 26 μg m^-3) cases during the nighttime suggest that a reduction in local PM₁₀ emissions is crucial to decrease the PM₁₀ concentration during high-PM₁₀ events. The high PM₁₀^S for daytime LRT cases can be explained by the combined effects of increased local emissions and LRT aerosols.

Atmospheric organophosphate esters in the Western Antarctic Peninsula over 2014-2018: Occurrence, temporal trend and source implication

Organophosphate esters (OPEs) were comprehensively investigated in the air samples collected using high-volume samplers near the Chinese Great Wall Station in the Western Antarctic Peninsula over the period of 2014-2018. The concentrations of ∑₈OPEs (gaseous + particle phases) ranged from 33.9 to 404 pg/m³ with a geometric mean of 119 ± 12.0 pg/m³. Tris [(2R)-1-chloro-2-propyl] phosphate (TCIPP) and tris(2-chloroethyl) phosphate (TCEP) dominated in the gaseous phase, while tris-n-butyl phosphate (TnBP) was the most abundant OPEs in the particle phase, followed by TCIPP and TCEP. An apparently temporal trend was observed for atmospheric ∑₈OPEs over the five years, with a doubling time of about 3.8 years, which indicated continuous inputs of OPEs into the sampling area. The particle-bound ∑₈OPEs accounted for 45% of the total, generally lower than that reported in the Arctic. Gas-particle partitioning modeling suggested that the partitioning of OPEs with higher logK_OA values approached the steady state in the Antarctic air. The back-trajectory modeling showed that high levels of OPEs were usually associated with air inputs from the northwest of the peninsula. This suggested that long-range transport from South America, which was confirmed by the no temperature dependencies of OPEs concentrations (excluding TnBP). Nevertheless, a steady high level of particle-bound TnBP implied local sources in the Western Antarctic Peninsula, which required further investigation in future works.

Natural archives of long-range transported contamination at the remote lake Letšeng-la Letsie, Maloti Mountains, Lesotho

Naturally accumulating archives, such as lake sediments and wetland peats, in remote areas may be used to identify the scale and rates of atmospherically deposited pollutant inputs to natural ecosystems. Co-located lake sediment and wetland cores were collected from Letšeng-la Letsie, a remote lake in the Maloti Mountains of southern Lesotho. The cores were radiometrically dated and analysed for a suite of contaminants including trace metals and metalloids (Hg, Pb, Cu, Ni, Zn, As), fly-ash particles, stable nitrogen isotopes, polycyclic aromatic hydrocarbons (PAHs) and persistent organic pollutants such as polychlorinated biphenyls (PCBs), polybrominated flame retardants (PBDEs) and hexachlorobenzene (HCB). While most trace metals showed no recent enrichment, mercury, fly-ash particles, high molecular weight PAHs and total PCBs showed low but increasing levels of contamination since c.1970, likely the result of long-range transport from coal combustion and other industrial sources in the Highveld region of South Africa. However, back-trajectory analysis revealed that atmospheric transport from this region to southern Lesotho is infrequent and the scale of contamination is low. To our knowledge, these data represent the first palaeolimnological records and the first trace contaminant data for Lesotho, and one of the first multi-pollutant historical records for southern Africa. They therefore provide a baseline for future regional assessments in the context of continued coal combustion in South Africa through to the mid-21st century.

Occurrence and distribution of organophosphate esters in the air and soils of Ny-Ålesund and London Island, Svalbard, Arctic

The levels of eight organophosphate esters (OPEs) were analyzed in air and soil samples collected at Ny-Ålesund and London Island, Svalbard during the Chinese Scientific Research Expedition to the Arctic during 2014-2015. The concentrations of total OPEs (∑OPEs) ranged from 357 pg/m³ to 852 pg/m³ in the air and from 1.33 ng/g to 17.5 ng/g dry weight (dw) in the soils. Non-Cl OPEs accounted for 56 ± 13% and 62 ± 16% of ∑OPEs for the air and soil, respectively. Tris(2-chloroethyl) phosphate (TCEP) was the dominant compound in the air, with an average concentration of 180 ± 122 pg/m³. Triphenyl phosphate, tri(1-chloro-2-propyl) phosphate, and TCEP were the most abundant OPEs in the soils, with mean values of 1.77, 2.13, and 1.02 ng/g dw, respectively. Compared with the levels of polybrominated diphenyl ethers found in Arctic regions in previous studies, OPEs showed significantly higher concentrations, thereby indicating the large production and wide usage of OPEs globally. In addition, the fugacity fraction results indicated that net deposition from air to soil was dominated in the area. Overall, the occurrence and distribution of OPEs in the air and soils in the Arctic region indicated that OPEs can undergo long-range atmospheric transport and accumulate in remote regions.

Long term trends of chemical constituents and source contributions of PM2.5 in Seoul

PM_2.5 was measured and analyzed between 2014 and 2015 in Seoul, and its sources were identified with a positive matrix factorization (PMF) to characterize chemical constituents and sources of the measured PM_2.5. To verify policy interventions in reducing PM_2.5 levels in Korea, the results were compared with previously published results from 2003 to 2007 at the same study site. A total of 215 PM_2.5 samples were collected and analyzed for 24 species, i.e., carbonaceous species (OCEC), ionic species (NO3-, SO42-, and NH4+), and 19 element species in this study. The average PM_2.5 mass concentration during the sampling period was 42.6±23.3 μg m-3. The seasonal average mass concentration of PM_2.5 was the highest during winter (49.9±20.6 μg m-3), followed by spring (45.2±25.3 μg m-3), fall (34.4±19.3 μg m-3), and summer (28.4±12.5 μg m-3). Nine sources were identified and quantified using the PMF model: secondary nitrate (19.0%), secondary sulfate (20.2%), mobile (23.3%), biomass burning (12.1%), soil (8.3%), roadway emissions (3.1%), aged sea salt (1.0%), coal combustion (4.1%), and oil combustion (9.0%). The PM_2.5 levels and chemical constituents during this study were lower than those during the previous study from 2003 to 2007. Particularly, concentrations of mobile related chemicals (OC, EC, and nitrate) and mobile source contributions consistently decreased from 2003 to 2015, indicating that the mobile emission reduction policy is improving PM_2.5 levels in the region. The comparison between the two periods allows trends in chemical constituents and the sources of PM_2.5 in Seoul to be understood.

Long-range transported North American wildfire aerosols observed in marine boundary layer of eastern North Atlantic

Wildfire is a major source of biomass burning aerosols, which greatly impact Earth climate. Tree species in North America (NA) boreal forests can support high-intensity crown fires, resulting in elevated injection height and longer lifetime (on the order of months) of the wildfire aerosols. Given the long lifetime, the properties of aged NA wildfire aerosols are required to understand and quantify their effects on radiation and climate. Here we present comprehensive characterization of climatically relevant properties, including optical properties and cloud condensation nuclei (CCN) activities of aged NA wildfire aerosols, emitted from the record-breaking Canadian wildfires in August 2017. Despite the extreme injection height of ~12 km, some of the wildfire plumes descended into the marine boundary layer in the eastern North Atlantic over a period of ~2 weeks, owing to the dry intrusions behind mid-latitude cyclones. The aged wildfire aerosols have high single scattering albedos at 529 nm (ω₅₂₉; 0.92-0.95) while low absorption Ångström exponents (Å_abs) at 464 nm/648 nm (0.7-0.9). In comparison, Å_abs of fresh/slightly aged ones are typically 1.4-3.5. This low Å_abs indicates a nearly complete loss of brown carbon, likely due to bleaching and/or evaporation, during the long-range transport. The nearly complete loss suggests that on global average, direct radiative forcing of BrC may be minor. Combining Mie calculations and the measured aerosol hygroscopicity, volatility and size distributions, we show that the high ω₅₂₉ and low Å_abs values are best explained by an external mixture of non-absorbing organic particles and absorbing particles of large BC cores (>~110 nm diameter) with thick non-absorbing coatings. The accelerated descent of the wildfire plume also led to strong increase of CCN concentration at the supersaturation levels representative of marine low clouds. The hygroscopicity parameter, κ_CCN, of the aged wildfire aerosols varies from 0.2 to 0.4, substantially lower than that of background marine boundary layer aerosols. However, the high fraction of particles with large diameter (i.e., within accumulation size ranges, ~100-250 nm) compensates for the low values of κ, and as a result, the aged NA wildfire aerosols contribute more efficiently to CCN population. These results provide direct evidence that the long-range transported NA wildfires can strongly influence CCN concentration in remote marine boundary layer, therefore the radiative properties of marine low clouds. Given the expected increases of NA wildfire intensity and frequency and regular occurrence of dry intrusion following mid-latitude cyclones, the influence of NA wildfire aerosols on CCN and clouds in remote marine environment need to be further examined.

Determining diurnal fossil fuel CO2 and biological CO2 by Δ14CO2 observation on certain summer and winter days at Chinese background sites

Diurnal atmospheric Δ¹⁴CO₂ was measured on two consecutive days in summer and winter, 2016 at Shangdianzi, Lin'an and Luhuitou regional background sites, and at Waliguan global background site in China. The objectives of this study were to determine diurnal fossil fuel CO₂ (CO_2ff) and biological CO₂ (CO_2bio) concentrations and to ascertain the factors influencing them. Evident CO_2ff inputs (0-33.0 ± 1.4 ppm) were found, with some small morning and afternoon rush hour signals. Particularly, the long-range transport of air masses influenced the seasonal differences and rapid diurnal variations in CO_2ff. Diurnal CO_2bio showed violent variations (-20.9-113.3 ppm), with high values at night and low or negative values during the daytime. Diurnal CO_2bio variations resulted from the tradeoffs between photosynthetic CO₂ uptake and biological respiration CO₂ emission as well as atmospheric boundary layer heights variations. These results might help to understand the roles of fossil fuel sources and biological sources on atmospheric CO₂ diurnal variations at Chinese background sites.

The risk of cross-border pollution and the influence of regional climate on the rainwater chemistry in the Southern Carpathians, Romania

The aim of this study is the assessment of rainwater composition, regarding the various sources of major ions and heavy metals, taking into account the characteristic atmospheric circulations and the main air mass transport routes. Rainwater samples were analyzed for pH, electrical conductivity, major ions, and heavy metals. At all sampling sites, the most abundant anions were SO₄^2- and Cl-, while the dominant cations were Ca²⁺ and Mg²⁺. Regarding heavy metals, the dominance of Pb and Cd was found. The contribution of soil dust from the mining activities and the dissolution of CaCO₃, MgCO₃, and CaSO₄·2H₂O in the rainwater explains the high concentrations of Ca²⁺, Mg²⁺, and SO₄^2-. The overall precipitation contamination with heavy metals at the three sampling sites was assessed by the degree of contamination, showing that Pb and Cd presents the highest risks of all heavy metals. The values of toxicity potential suggested an elevated risk for human health in case of rainwater ingestion, especially in rural areas. Spearman correlation and PCA indicated that the chemical characteristic of the rainwater is primarily controlled by sources such as agricultural activities, mixed and crustal sources, traffic, and other anthropogenic, industrial influences, mining activities, smelting operations, coal combustion, and metal production.

Revealing the impacts of transboundary pollution on PM2.5-related deaths in China

Long-range transport of air pollutants may cause significant health impacts in the receptor regions. In this study, we calculated the transboundary health impact from different foreign regions using a state-of-the-art air quality model at hemispheric scale. Our results reveal that transboundary PM_2.5 pollution from outside China was of great significance, causing 100 thousand (95% CI, 45 thousand-200 thousand) premature deaths in China in 2015, which accounted for 9.60% PM_2.5 related premature death in China. The impact of transboundary pollution in China was most significant in winter, in which the average PM_2.5 concentration increased by 3.7 μg/m³, and was least significant in summer, with the average PM_2.5 concentration increasing by 0.5 μg/m³. Liaoning and Yunnan provinces were extremely susceptible to transboundary pollution, whose annual average PM_2.5 concentrations were increased by 10.2 and 11.4 μg/m³ respectively. Among all foreign regions, the impact from South Asia was most significant, causing 30 thousand (95% CI, 12 thousand-62 thousand) premature deaths annually in China. This study only reveals the transboundary impact under the integrated exposure-response (IER) model and fixed meteorology field in 2015. Further studies are needed to investigate how different exposure-response functions and meteorology affect the transboundary PM_2.5 pollution and its related death.

Urban black carbon - source apportionment, emissions and long-range transport over the Brahmaputra River Valley

This research investigates whether the vehicular black carbon emissions originated in the North-Eastern city of Guwahati are transported over and in the Brahmaputra River Valley and the Himalayas. The total black carbon was apportioned between the fossil fuel and biomass burning by real-time measurements of black carbon concentrations at two distinct locations having different traffic volumes in 2016-17. The average observed BC concentrations were 20.58, 6.42, 3.50 and 5.29 μg/m³ at the low traffic location and 22.44, 17.14, 9.2 and 16.87 μg/m³ at the high traffic location in winter, pre-monsoon, monsoon and post-monsoon seasons, respectively. Temperature, wind speed, and solar radiation were found to have significant negative correlations with BC concentrations, while relative humidity had positive correlations. It was found that vehicles contributed over 85% of the ambient black carbon at both locations. Black carbon emission from this dominant source was estimated for 2018, which showed that from vehicles it increased to 0.44-0.55 Gg in 2018 from 0.29 to 0.33 Gg in 2011, which may result in the adverse impacts on the eco-sensitive Brahmaputra River Valley and the Himalayas. The transport and deposition of black carbon under different climatic seasons was modelled using HYSPLIT. The results showed that black carbon particulates are being transported and deposited all-round the year in the Himalayas and the surrounding region. Pre-monsoon and monsoon seasons contributed to the largest amounts of deposition, and a clear relation was found between deposition and rainfall. The total BC deposited in the Brahmaputra River Valley and the Himalayas during one year was 22,142.69 kg and 1566.53 kg with average deposition rates of 0.6452 μgm^-2 day^-1 and 0.0182 μgm^-2 day^-1, respectively.

Halogenated flame retardants in the sediments of the Chinese Yellow Sea and East China Sea

With the phasing out of traditional polybrominated diphenyl ethers (PBDEs), significant volumes of alternative brominated flame retardants (aBFRs) are being used and released into the environment compartment, especially in coastal regions. The levels and distribution of PBDEs, aBFRs, and dechlorane plus (DPs) were investigated in the surface sediments of the Yellow Sea (YS) and East China Sea (ECS) to examine the distribution and sources of these hydrophobic contaminants. The level and distribution of pollutants in the sediments of YS and ECS show obvious regional differences. As a major replacement for decabromodiphenyl ether (BDE 209), decabromodiphenyl ethane (DBDPE) was the dominant compound observed in the surface sediments, with a concentration one order of magnitude higher than that of BDE 209. High concentrations were found in the depositional zones of the YS, indicating that these contaminants may originate from land-based pollution sources (likely from the Laizhou Bay manufacturing base) near the Bohai Sea. The pollutants can be carried by the coastal current together with the sediment from the Yellow River, transported through the Bohai Strait and deposited in the mud zone of Northern and Southern YS. Low levels of halogenated flame retardants (HFRs) were found in the estuary of the Yangtze River and ECS, indicating that Yangtze River contributes less HFRs to the region. Riverine discharge, atmospheric deposition, surface runoff, ocean current system, and mud area deposition effects may be significant factors influencing the distributions of HFRs.

Carbonaceous aerosol characteristics on the Third Pole: A primary study based on the Atmospheric Pollution and Cryospheric Change (APCC) network

Carbonaceous aerosols (CAs) scatter and absorb incident solar radiation in the atmosphere, thereby influencing the regional climate and hydrological cycle, particularly in the Third Pole (TP). Here, we present the characteristics of CAs at 19 observation stations from the Atmospheric Pollution and Cryospheric Change network to obtain a deep understanding of pollutant status in the TP. The organic carbon (OC) and elemental carbon (EC) concentrations decreased noticeably inwards from outside to inland of the TP, consistent with their emission load and also affected by transport process and meteorological condition. Urban areas, such as Kathmandu, Karachi, and Mardan, exhibited extremely high OC and EC concentrations, with low and high values occurring in the monsoon and non-monsoon seasons, respectively. However, remote regions inland the TP (e.g., Nam Co and Ngari) demonstrated much lower OC and EC concentrations. Different seasonal variations were observed between the southern and northern parts of the TP, suggesting differences in the patterns of pollutant sources and in distance from the sources between the two regions. In addition to the influence of long-range transported pollutants from the Indo-Gangetic Plain (IGP), the TP was affected by local emissions (e.g., biomass burning). The OC/EC ratio also suggested that biomass burning was prevalent in the center TP, whereas the marginal sites (e.g., Jomsom, Dhunche, and Laohugou) were affected by fossil fuel combustion from the up-wind regions. The mass absorption cross-section of EC (MAC_EC) at 632 nm ranged from 6.56 to 14.7 m² g^-1, with an increasing trend from outside to inland of the TP. Urban areas had low MAC_EC values because such regions were mainly affected by local fresh emissions. In addition, large amount of brown carbon can decrease the MAC_EC values in cities of South Asia. Remote sites had high MAC_EC values because of the coating enhancement of aerosols. Influenced by emission, transport process, and weather condition, the CA concentrations and MAC_EC presented decreasing and increasing trends, respectively, from outside to inland of the TP.

Long-range transport potential and atmospheric persistence of cyclic volatile methylsiloxanes based on global measurements

This study investigates persistence (P) and long-range transport potential (LRTP) of cyclic volatile methylsiloxanes (cVMS) based on the field measurements in the Northern Hemisphere. The field data consisted of published outdoor air concentrations of octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5) and dodecamethylcyclohexasiloxane (D6) at urban, suburban, rural and remote locations excluding the point sources. Three major trends were observed. First, D4 and D6 concentrations were correlated with measured concentrations for D5 at the same times and locations in the majority of the datasets, reflecting the common sources and similar removal mechanism(s) for these compounds. Second, as the sampling sites changed from the source to remote locations along a south-to-north transect, average cVMS concentrations in air decreased in an exponential manner. The empirical characteristic travel distances (eCTD) extracted from these spatial patterns were smaller than model estimated values and differed in order among individual compounds (D4 ∼ D5 < D6). Finally, D5/D6 concentration ratios were also found to decrease exponentially along the same spatial gradient, contrary to model predictions of an increase based on current knowledge of mechanisms controlling atmospheric cVMS degradation. These findings suggest that there may be additional removal process(es) for airborne cVMS, currently not accounted for, that requires further elucidation.

Impacts of hazardous metals and PAHs in fine and coarse particles with long-range transports in Taipei City

This study assessed the impact on air quality and health risk by long-range transported (LRT) PM_2.5-10- and PM_2.5-bound metals and PAHs in Taipei City, Taiwan. Several methods with receptor aerosol measurements were used to quantify the effect of LRT. The hybrid single particle lagrangian integrated trajectory model (HYSPLIT) was used in conjunction with the potential source contribution function (PSCF) to distinguish the LRT aerosols. By using a general linear model (GLM) with a marginal mean and positive matrix fraction (PMF), this study also evaluated the annual increased level of LRT (AIR_LRT) for each source contribution to the concentration and the resultant health risk of particle-bound metals and polycyclic aromatic hydrocarbons (PAHs). The LRT influenced fine-sized metals and PAHs rather than coarse-sized ones. We found that the level of PM_2.5-bound toxic metals (Pb, Cd, and As) and PAHs (Benzo[a]pyrene and dibenzo[a,e]pyrene) could increase by 90% under the influence of LRT in 2014, while an AIR_LRT value of 25% for the PM_2.5 mass concentration was observed. Overall, the excess cancer risk (ECR) resulting from PM_2.5-bound metal and PAH exposures was 6.40 × 10^-5 in relation to coal combustions (20.7%), traffic-related emissions (59.7%) and re-suspended aerosols (19.6%). Among these contributors, LRT-related metals and PAHs in PM_2.5 accounted for 51% of the total ECR.

Influence of peat fires on the rainwater chemistry in intra-mountain basins with specific atmospheric circulations (Eastern Carpathians, Romania)

A comprehensive study on the chemical composition of precipitation, the influence of peat fires and their relations with atmospheric circulation was conducted in the year of 2012, in two intra-mountain basins, the Ciuc basin (CB) and the Giurgeu basin (GB), Eastern Carpathians, Romania. Atmospheric circulation types showed the presence of a westerly anticyclonic circulation, characterized by a strong development of the Azores High to the northern Atlantic, contributing to the appearance of peat-fires. Using ROCADA daily gridded climatic datasets, the maximum and minimum daily temperatures were extracted, showing deviation from 2 °C to 6 °C in the studied year against the multiannual mean for the 1981-2016 period. Rainwater samples were analyzed for pH, major anions and cations; HCO₃^- concentrations were calculated based on the empirical relationship between pH and HCO₃^-. The results showed that 45.16% and 54.55% of precipitation had pH > 7.0 at CB and GB, respectively. NH₃, NH₄⁺ and Ca²⁺ are the main neutralizing agents. The significant correlation between SO₄^2- and NH₄⁺ (r = 0.711 - CB; r = 0.736 - GB) indicated neutralization by NH₃ in the forms of (NH4)₂SO₄ and NH₄HSO₄. Positive regression coefficient between the sum of (H⁺ + [NH₄⁺] + [Ca²⁺]) and the sum of ([nss - SO₄^2-] + [NO₃^-]) (r = 0.855 - CB; r = 0.796 - GB), showed that acid neutralization was primarily brought by NH₄⁺ and/or CaCO₃. Using Na as an indicator of marine origin, the proportions of sea salt and non-sea-salt were estimated from elemental ratios. According to correlation analysis and PCA, main acidic ions (SO₄^2- and NO₃^-) and NH₄⁺ were mainly derived from anthropogenic activities (biomass burning, peat fires, fertilization), while Ca²⁺ and Mg²⁺ originated from terrestrial sources. The behavior of gaseous pollutants and smoke distribution resulted from peat fires were deciphered using the HYSPLIT model in a case study.

The effect of long-range transport, trophic position and diet specialization on legacy contaminant occurrence in great skuas, Stercorarius skua, breeding across the Northeast Atlantic

High levels of halogenated organic contaminants (HOCs) have been found in the marine predatory seabird great skua (Stercorarius skua) from breeding colonies in the Northeastern Atlantic, with large unexplained inter-colony variation. The present study aimed at analyzing if the HOCs occurrence in breeding great skuas in remote colonies was explained by local baseline food web exposure determined by long-range transport, or by ecological factors such as diet specialization and relative trophic position in the breeding area. The occurrence of organochlorine pesticides (OCPs), polychlorinated biphenyls (PCBs), and polybrominated diphenyl ethers (PBDEs) was analyzed in plasma of 204 adult great skuas collected over two years (2008 and 2009) and 5 colonies across the North-Atlantic from Shetland to Svalbard. The ΣHOCs levels in plasma ranged across two orders of magnitude, from 40 to 7600 ng/g (wet weight) and differed significantly across the great skua colonies. The variation in contaminant occurrence among colonies did not reflect long-range transport through a latitudinal or remoteness gradient, as the second northernmost colony (Bjørnøya), had the highest contaminant concentrations. No latitudinal or remoteness gradient was evident in the contaminant pattern among the colonies. The contaminant levels increased significantly with increasing δ¹⁵N values, and regurgitated pellets of undigested prey suggested that great skuas with higher δ¹⁵N values had a higher proportion of bird prey in their diet, mostly seabirds. In contrast, great skuas from colonies with lower δ¹⁵N and lower contaminant level fed mostly on fish. The enrichment of δ¹³C increased with decreasing δ¹⁵N and lower contaminant levels. Therefore, individual behavior of great skuas, such as migration strategies and diet specialization, rather than long-range transport and thus baseline food web exposure, explain among and within colony variance in contaminant occurrence.

Impact of field biomass burning on local pollution and long-range transport of PM2.5 in Northeast Asia

Biomass burning (BB), such as, crop field burning during the post-harvest season, emits large amounts of air pollutants (e.g., PM_2.5) that severely impact human health. However, it is challenging to evaluate the impact of BB on PM_2.5 due to uncertainties in the size and location of sources as well as their temporal and spatial variability. This study focused on the impacts of BB on local pollution as well as the long-range transport of PM_2.5 in Northeast Asia resulting from a huge field BB event in Northeast China during the autumn of 2014. Air quality simulations using the Community Multiscale Air Quality (CMAQ) model were conducted in the year 2014 over the horizontal domains covering Northeast Asia, including the Japanese mainland. In the baseline simulation (Base), field BB emissions were derived from Fire INventory from NCAR (FINN) v1.5 for the year 2014. The model reasonably captured the daily mean PM_2.5 mass concentrations, however, it underestimated concentrations in autumn around Northeast China where irregular field BB following the harvest occurred frequently. To address the underestimation of emissions from BB sources in China, another simulation with boosted BB sources from cropland area (FINN20_crop) was conducted in addition to the Base simulation. The model performance of FINN20_crop was significantly improved and showed smaller biases and higher indices of agreement between simulated and observed values in comparison to those of Base. To evaluate long-range transport of PM_2.5 from BB sources in China towards Japan, CMAQ with brute-force method (CMAQ/BFM)-estimated BB contributions for Base and FINN20_crop cases were compared with Positive Matrix Factorization (PMF)-estimated BB contributions at Noto Peninsula in Japan. The CMAQ/BFM-estimated contributions from FINN20_crop were in greater agreement with the PMF-estimated contributions. The comparison of BB contributions estimated by the two contrasting models also indicated large underestimations in the current BB emission estimates.

Quantifying PM2.5 from long-range transport and local pollution in Taiwan during winter monsoon: An efficient estimation method

From autumn to the following spring, annually, the northeast monsoon transports PM_2.5 (particles less than 2.5 μm in aerodynamic diameter) from the Asian continent to downstream areas. Naturally, this triggered a question: What are the contributions of PM_2.5 from long-range transport (LRT) and local pollution (LP) at any downstream location? To answer that question, the present study developed an economical and efficient method that can easily estimate the contribution of PM_2.5 from LRT (LRT-PM_2.5) and PM_2.5 from LP (LP-PM_2.5). The method used PM_2.5 and meteorological observation data in Taiwan from 2006 to 2015 and a short-term simulation from January to May in 2010. The analysis classified the data into three types of PM_2.5 source patterns: LRT-Event (high concentration plume at the front edge of southward moving anticyclones/strong northeast wind), LRT-Ordinary (less concentration in common strong northeast wind), and LRT/LP Mix or Pure LP (PM_2.5 was from both LRT and LP or from only LP under weak northeast wind). During the ten-year period, the average LRT-PM_2.5 values at the northern tip of Taiwan were 31-39 μg m^-3, 12-16 μg m^-3, and 4-13 μg m^-3 for the LRT-Event, LRT-Ordinary, and LRT/LP Mix or Pure LP patterns, respectively. The 10-year average LRT-PM_2.5 and LP-PM_2.5 contributions were approximately 70:30 in northern Taiwan, 50:50 in central Taiwan, and 30:70 in southern Taiwan for the LRT-Event pattern; 60:40 in northern and 40:60 in central and southern Taiwan for the LRT-Ordinary pattern; and 30:70 in northern and 25:75 in central and southern Taiwan for the LRT/LP Mix or Pure LP pattern. Interestingly, LRT-PM_2.5 peaked in 2013 but has decreased annually since then, whereas LP-PM_2.5 has roughly decreased in the past ten years.

Industrial and natural compounds in filter-feeding black fly larvae and water in 3 tundra streams

We report concentrations of polychlorinated biphenyls, polybrominated diphenyl ethers, novel flame retardants, and naturally occurring bromoanisoles in water and filter-feeding black fly (Simuliidae) larvae in 3 tundra streams in northern Sweden. The results demonstrate that black fly larvae accumulate a wide range of organic contaminants and can be used as bioindicators of water pollution in Arctic streams. Environ Toxicol Chem 2018;37:3011-3017. © 2018 SETAC.

Global distribution potential and regional environmental risk of F-53B

Recent years have witnessed increases in emissions and environmental contamination by F-53B, a chlorinated polyfluorinated ether sulfonate used as a mist suppressant in the Chinese electroplating industry. In this study, based on a national industrial survey and statistics, we estimated the annual release of F-53B across China during the period 2006-2015. We evaluated the global transport and distribution of F-53B using the Globo-POP model, and assessed its environmental risk in regions of China using the EUSES model. Our calculations indicate that approximately 10-14 metric tons (t) of F-53B are released annually into the environment, mainly in East China. Our Globo-POP calculations demonstrate that a limited fraction (0.02-0.50%) of the cumulative F-53B emissions can reach the Arctic via oceanic advection. Despite its low long-range transport potential, F-53B can accumulate in Chinese local waters. Our EUSES calculations predict that the F-53B concentration in fresh water (South China) currently approaches 0.7 mg/L and will reach 2.3 mg/L by 2020 in the region surrounding chromium-plating plants if its use remains uncontrolled. Such an increase in concentration implies a potential risk to aquatic environments. This study highlights the risk if F-53B is proposed to be used as a substitute for perfluorooctanesulfonic salt-based mist suppressants.

Comparison of PM2.5 chemical composition and sources at a rural background site in Central Europe between 1993/1994/1995 and 2009/2010: Effect of legislative regulations and economic transformation on the air quality

From December 1993 to January 1995 and from October 2009 to October 2010, a total of 320 and 365 daily samples of the PM_2.5 were collected at a rural background site (National Atmospheric Observatory Košetice) in Central Europe. The PM_2.5 samples were analyzed for 29 and 26 elements respectively by Particle-Induced X-ray Emission (PIXE) and water-soluble inorganic ions by Ion Chromatography (IC) in 2009/2010. The Positive Matrix Factorization (PMF) was applied to the chemical composition of PM_2.5 to determine its sources. The decreasing trends of almost all elements concentrations, especially the metals regulated by the EU Directive (2004/107/EC) are evident. The annual median ratios indicate a decrease in concentrations of the PM_2.5 elements. The slight increase of K concentrations and Spearman's rank correlation coefficient r_s 0.09 K/Se points to a rise in residential wood combustion. The S concentrations are nearly comparable (higher mean in 2009/2010, while the annual median ratio is under 1). The five major source types in the mid-1990s were ascribed to brown coal combustion, oil combustion, sea salt and dust - long-range transport, re-suspended dust and black coal combustion. The industrial combustion of brown and/or black coal (r_s 0.75 Se/As, r_s 0.57 Ga/Ge and r_s 0.20 As/Zn) and oil (r_s 0.72 V/Ni) of the regional origin dominated. In the 1990s, the potential source regions were the border area of Czech Republic, German and Poland (brown coal), the Moravia-Silesia region at the Czech-Polish border (black coal), and Slovakia, Austria, Hungary, and the Balkans (oil). In 2009/2010, the apportioned sources were sulfate, residential heating, nitrate, industry, re-suspended dust, and sea salt and dust - long-range transport. The secondary sulfate from coal combustion and residential biomass burning (r_s 0.96, K/K⁺) of local origin dominated. The declining trend of the elemental concentrations and change in the source pattern of the regional background PM2.5 in Central Europe between the mid-1990s and 2009/10 reflects the economic transformation and impact of stricter legislation in Central Europe.

Chemical characterisation and source identification of atmospheric aerosols in the Snowy Mountains, south-eastern Australia

Characterisation of atmospheric aerosols is of major importance for: climate, the hydrological cycle, human health and policymaking, biogeochemical and palaeo-climatological studies. In this study, the chemical composition and source apportionment of PM_2.5 (particulate matter with aerodynamic diameters less than 2.5μm) at Yarrangobilly, in the Snowy Mountains, SE Australia are examined and quantified. A new aerosol monitoring network was deployed in June 2013 and aerosol samples collected during the period July 2013 to July 2017 were analysed for 22 trace elements and black carbon by ion beam analysis techniques. Positive matrix factorisation and back trajectory analysis and trajectory clustering methods were employed for source apportionment and to isolate source areas and air mass travel pathways, respectively. This study identified the mean atmospheric PM_2.5 mass concentration for the study period was (3.3±2.5)μgm^-3. It is shown that automobile (44.9±0.8)%, secondary sulfate (21.4±0.9)%, smoke (12.3±0.6)%, soil (11.3±0.5)% and aged sea salt (10.1±0.4)% were the five PM_2.5 source types, each with its own distinctive trends. The automobile and smoke sources were ascribed to a significant local influence from the road network and bushfire and hazard reduction burns, respectively. Long-range transport are the dominant sources for secondary sulfate from coal-fired power stations, windblown soil from the inland saline regions of the Lake Eyre and Murray-Darling Basins, and aged sea salt from the Southern Ocean to the remote alpine study site. The impact of recent climate change was recognised, as elevated smoke and windblown soil events correlated with drought and El Niño periods. Finally, the overall implications including potential aerosol derived proxies for interpreting palaeo-archives are discussed. To our knowledge, this is the first long-term detailed temporal and spatial characterisation of PM_2.5 aerosols for the region and provides a crucial dataset for a range of multidisciplinary research.

Arctic source for elevated atmospheric mercury (Hg0) in the western Bering Sea in the summer of 2013

Measurements of gaseous elemental mercury (Hg⁰) in the marine boundary layer of the western Bering Sea were performed using an automatic mercury analyzer RA 915+ (Ltd. "Lumex", St. Petersburg, Russia) aboard the Russian research vessel Academician M.A. Lavrentev from 3 to 20 August 2013. Hg⁰ concentrations varied from 0.3 to 2.1ng/m³ (n=4783); the average value (1.1±0.3ng/m³) was lower than both the background range of the Northern Hemisphere (1.5-1.7ng/m³) and average values previously observed in the Bering Sea, and corresponded to the background concentrations of the Southern Hemisphere (1.1-1.3ng/m³). Maximum Hg⁰ concentrations were observed within air masses that came from the lower troposphere of the central Arctic. Under these conditions, Hg⁰ ranged between 1.1 and 2.1ng/m³ with an average of 1.5±0.2ng/m³ (n=1183). Except for these periods, Hg⁰ concentrations during the rest of the study varied from 0.3 to 1.8ng/m³, with an average value of 1.0±0.2ng/m³ (n=3600). Our results support the hypothesis that, in the summer, air masses from the central Arctic Ocean can be an exporter of mercury to lower latitudes. Perhaps the atmospheric transport of elevated concentrations of Hg⁰ into lower latitudes may have implications for the biologic and economic health of important fisheries, such as the Bering Sea.