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.

Fate of organophosphate esters from the Northwestern Pacific to the Southern Ocean: Occurrence, distribution, and fugacity model simulation

Eleven organophosphate esters (OPEs) in the air and seawater were investigated from the northwestern Pacific Ocean to the Southern Ocean during the 2018 Chinese 34th Antarctic Scientific Expedition. The concentration of total OPEs ranged from 164.82 to 3501.79 pg/m3 in air and from 4.54 to 70.09 ng/L in seawater. Two halogenated OPEs, tri(chloropropyl) phosphate (TCPP) and tri (2-chloroethyl) phosphate (TCEP), were generally more abundant than the non-halogenated OPEs. A level III fugacity model was developed to simulate the transfer and fate of seven OPEs in the air and seawater regions of the central Ross Sea. The model results indicate that OPEs are transferred from the air to the seawater in the central Ross Sea in summer, during which the Ross Sea acts as a final OPE sink. Dry and wet deposition dominated the processes involving OPE transfer to seawater. The OPE degradation process was also found to be more pervasive in the atmosphere than in the seawater region. These findings highlights the importance of long-range transport of OPEs and their air-seawater interface behavior in the Antarctic.

Long-term monitoring of atmospheric PCDD/Fs at Mount Lulin during spring season: PCDD/F source apportionment through a simultaneous measurement in Southeast Asia

A long term assessment of atmospheric polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) at Mt. Lulin, located in center of Taiwan was carried out from 2008 to 2013 (n = 81) assuming Mt. Lulin to be background area. During monitoring processes, PCDD/F samples collected in the field occasionally reached high concentration. To investigate this situation, simultaneous sample collection was carried out in Southeast Asia countries (i.e., Vietnam and Thailand) and Taiwan in 2013. The average concentration of atmospheric PCDD/Fs in biomass-burning source regions, namely Son La and Doi Ang Khang were 19.8 ± 12.1 fg I-TEQ m^-3 (n = 19) and 17.8 ± 12.4 fg I-TEQ m^-3 (n = 20), respectively. In the downwind area of Mt. Lulin, the average concentration of PCDD/Fs was found to be 4.64 ± 3.77 fg I-TEQ m^-3 (n = 18). PCDD/F concentration in the source region was much higher than that in the downwind region. On March 19, 2013, the atmospheric PCDD/F concentrations increased dramatically from 7.71 to 484 fg I-TEQ m^-3 at Mt. Lulin, which many times exceeded that of assumed source region in Southeast Asia. Moreover, mainland Southeast Asia and the southeast coast of China was suspected to be the main contributors of atmospheric PCDD/Fs and biomass markers, such as nonsea-salt K⁺ and NH₄⁺, during the spring. WRF-Chem and Potential Source Contribution Function (PSCF) simulations have confirmed this correlation. It can be concluded that atmospheric PCDD/Fs observed at Mt. Lulin during spring mostly derived from the air mass transport not only from Southeast Asia but also the southeast coast of China.

Wet deposition of total dissolved nitrogen in Indo-Gangetic Plain (India)

Very limited information on the magnitude and environmental impacts of both inorganic and organic forms of nitrogen (N) wet deposition is available in India. Molar concentrations of inorganic (NH₄⁺ and NO₃^-) and organic N in rainwater were monitored at three different land use sites in Indo-Gangetic Plain (IGP) during the monsoon period (June-September) of 2017. It has been observed that dissolved organic N (DON) contributed significantly to the total dissolved N (TDN) ranging from 5 to 60%. Dissolved inorganic N (DIN = NH₄⁺ + NO₃^-) concentration was recorded as high as 221.0 μmol L^-1 at urban site to as low as 65.9 μmol L^-1 at the rural site. A similar pattern was also observed for DON. NH₄⁺ contribution to TDN had the order urban megacity (65%) > urban (70%) > rural (75%). Agriculture and animal husbandry are the primary sources of NH₄⁺ emissions in the rural site. However, NO₃^- has shown a contrasting trend at these sites (25%, 15%, and 8%, respectively). Wet deposition fluxes of atmospheric TDN were observed to be higher at urban sites. This can be attributed to a variety of local sources such as vehicular emission, microbial emissions, biomass burning, human excreta due to higher population density, and transportation from surrounding areas, as observed from concentration weighted trajectories (CWT) model and cluster analysis. Upwind region of IGP has experienced major influence of air mass transported from agriculturally rich northwest part of India. However, both the downwind sites have experienced by-and-large the influence of south-westerly air masses originated over the Arabian Sea. This study has found that the DON contributes significantly to TDN, and therefore, its inclusion for nitrogen budget assessment in South Asia is emphasized.

Model predictions of toxaphene degradation in the atmosphere over North America

Technical toxaphene, a broad-spectrum pesticide mixture, degrades in the environment, resulting in potential changes in toxicity. The present study uses a multimedia model that the authors developed to estimate toxaphene degradation in the atmosphere over North America. The predicted degradation has strong spatial and temporal variability determined by processes such as emission and transport of technical toxaphene, as well as the complex interactions among many species (e.g., toxaphene, hydroxyl [OH] radicals, and ozone). More toxaphene is degraded in warmer months due to higher concentrations of technical toxaphene (primarily due to higher technical toxaphene emissions in the southeastern United States and transport to other regions) and OH radicals. In the model, OH radicals are created primarily through the reactions of water vapor with the excited oxygen atom, O(¹D), generated by the photolysis of ozone, which is produced primarily by reactions of volatile organic compounds and nitrogen oxides (NOx) in the presence of sunlight. The higher OH concentrations in warmer months are primarily the result of higher solar radiation and ozone concentrations. The spatial distribution of degradation depends on the distribution of technical toxaphene soil residues as well as atmospheric transport and chemistry; significant chemical degradation occurs in the southeastern United States where soils are most heavily contaminated by past applications of toxaphene.

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.

Characteristics and source attribution of PM2.5 during 2016 G20 Summit in Hangzhou: Efficacy of radical measures to reduce source emissions

A field campaign was conducted to study the PM_2.5 and atmospheric gases and aerosol's components to evaluate the efficacy of radical measures implemented by the Chinese government to improve air quality during the 2016 G20 Summit in Hangzhou China. The lower level of PM_2.5 (32.48 ± 11.03 µg/m³) observed during the control period compared to pre-control and post-control periods showed that PM_2.5 was alleviated by control policies. Based on the mass concentrations of particulate components, the emissions of PM_2.5 from local sources including fossil fuel, coal combustion, industry and construction were effectively reduced, but non-exhaust emission was not reduced as effectively as expected. The accumulation of SNA (SO₄^2-, NO₃^-, NH₄⁺) was observed during the control period, due to the favourable synoptic weather conditions for photochemical reactions and heterogeneous hydrolysis. Because of transboundary transport during the control period, air masses from remote areas contributed significantly to local PM_2.5. Although, secondary organic carbon (OC_sec) exhibited more sensitivity than primary organic carbon (OC_pri) to control measures, and the increased nitrogen oxidation ratio (NOR) implied the regional transport of aged secondary aerosols to the study area. Overall, the results from various approaches revealed that local pollution sources were kept under control, indicating that the implementation of mitigation measures were helpful in improving the air quality of Hangzhou during G20 summit. To reduce ambient levels of PM_2.5 further in Hangzhou, regional control policies may have to be taken so as to reduce the impact of long-range transport of air masses from inland China.

Gaseous elemental mercury and its evasion fluxes in the marine boundary layer of the marginal seas of the northwestern Pacific: Results from two cruises in September-December 2019

There are many questions regarding the behavior of mercury in the sea-atmosphere system of the northwestern Pacific. Continuous underway measurements of atmospheric gaseous elemental mercury (GEM) and measurements of sea-air GEM evasion fluxes were carried out in the marginal seas of northwestern Pacific from the South China Sea to the Sea of Okhotsk in fall-winter 2019. The median GEM concentration (1.1 ng/m³) was lower than both the background value and the averages previously observed in these areas. A latitudinal gradient of atmospheric GEM and GEM evasion fluxes with maximum values at southern latitudes was found. The following areas have been identified as potential source areas: the Kurill area of the Pacific Ocean Northeast China, Korean Peninsula, and the territory from the southwest coast of the Yellow Sea to the south of Indochina. Seasonal variations were observed in the Sea of Japan and East China Sea with higher GEM concentrations in winter than in fall. Our data and analysis of published data showed significant relationships between GEM evasion fluxes, latitude and sea surface temperature (SST). It seems that on a global scale, along with the GEM gradient between water and atmosphere, SST is the most significant parameter for sea-air GEM evasion fluxes.

Unraveling the sources of ground level ozone in the Intermountain Western United States using Pb isotopes

Ozone as an atmospheric pollutant is largely produced by anthropogenic precursors and can significantly impact human and ecosystem health, and climate. The U.S. Environmental Protection Agency has recently proposed lowering the ozone standard from 75 ppbv (MDA8 = Maximum Daily 8-Hour Average) to between 65 and 70 ppbv. This will result in remote areas of the Intermountain West that includes many U.S. National Parks being out of compliance, despite a lack of significant local sources. We used Pb isotope fingerprinting and back-trajectory analysis to distinguish sources of imported ozone to Great Basin National Park in eastern Nevada. During discrete Chinese Pb events (> 1.1 ng/m(3) & > 80% Asian Pb) trans-Pacific transported ozone was 5 ± 5.5 ppbv above 19 year averages for those dates. In contrast, concentrations during regional transport from the Los Angeles and Las Vegas areas were 15 ± 2 ppbv above the long-term averages, and those characterized by high-altitude transport 3 days prior to sampling were 19 ± 4ppbv above. However, over the study period the contribution of trans-Pacific transported ozone increased at a rate of 0.8 ± 0.3 ppbv/year, suggesting that Asian inputs will exceed regional and high altitude sources by 2015-2020. All of these sources will impact regulatory compliance with a new ozone standard, given increasing global background.

Polycyclic aromatic hydrocarbons (PAHs) determined by pine needles and semipermeable membrane devices along an altitude profile in Taurus Mountains, Turkey

Polycyclic aromatic hydrocarbons (PAHs) were analyzed at different altitudes of Taurus Mountains in semipermeable membrane devices (SPMD) and in half-, one-and-a-half-, and two-and-a-half-year-old pine needles. SPMDs were deployed for three different exposure periods: March to September (Summer), September to March (Winter), and March to March (whole year) at eight sites where needle samples were collected. The values of PAHs in needles were between 4.4 to 6066 pg g/fw in half-year-old, 7.2 to 111,115 pg g/fw in 1.5-year-old, and 9.7 to 85,335 pg g/fw in 2.5-year-old needles. Mass of PAHs collected by SPMDs varied from <MDL to 8060 ng/SPMD in winter, from 0.98 to 585 ng/SPMD in summer, and <MDL to 9360 ng/SPMD in whole year deployment, respectively. PAH profiles were dependent on the seasonal differences and locations. Roughly, clear decreasing trends with altitude were observed both with SPMD and needles for many individual and groups of PAHs except for the SPMD-summer short-time data. A cross-plot of Fluo/(Fluo+Pyr) vs Ant/(Ant+Phe) diagnostic ratios indicated grass/wood burning (possibly due to forest fires) in summer and petrogenic combustion in winter. Results of the study showed that SPMD and conifer needles are effective passive samplers to measure PAHs in the environment.

Assessment of long-range transboundary aerosols in Seoul, South Korea from Geostationary Ocean Color Imager (GOCI) and ground-based observations

To better understand air quality issues in South Korea, it is essential to identify the main contributors of air pollution and to quantify the effects of transboundary transport. In this study, geostationary satellite measurements were used to assess the effects of aerosol transport on air quality in South Korea. This study proposes a method to define the long-range transport (LRT) of aerosols into the Korean Peninsula using remote sensing obervations and back-trajectories and estimates the LRT effects on air quality in Seoul using in-situ particulate matter (PM) measurements. Aerosol optical depths (AODs) are obtained from the Geostationary Ocean Color Imager (GOCI), and the back-trajectories are from the National Ocean and Atmospheric Administration (NOAA) HYbrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model. For LRT events, satellite observations showed high AOD plumes over the Yellow Sea, a pathway between Eastern China and South Korea, and the movements of aerosol plumes transported to South Korea were also detected. PM_2.5 concentrations, PM₁₀ concentrations, and AOD during LRT increased by 52%, 49%, and 81%, respectively, relative to their average values for 2015-2018. To quantitatively characterize the LRT of aerosols, the effects of LRT on PM_2.5 concentrations were estimated for each PM concentration category. The contribution of LRT to PM_2.5 concentrations was estimated to be 33% during 2015-2018. When high concentrations of PM_2.5 were observed in Seoul, they were likely to be associated with LRT events.

Identifying sources of ozone to three rural locations in Nevada, USA, using ancillary gas pollutants, aerosol chemistry, and mercury

Ozone (O3) is a secondary air pollutant of long standing and increasing concern for environmental and human health, and as such, the US Environmental Protection Agency will revise the National Ambient Air Quality Standard of 75 ppbv to ≤ 70 ppbv. Long term measurements at the Great Basin National Park (GBNP) indicate that O3 in remote areas of Nevada will exceed a revised standard. As part of the Nevada Rural Ozone Initiative, measurements of O3 and other air pollutants were made at 3 remote sites between February 2012 and March 2014, GBNP, Paradise Valley (PAVA), and Echo Peak (ECHO). Exceptionally high concentrations of each air pollutant were defined relative to each site as mixing ratios that exceeded the 90th percentile of all hourly data. Case studies were analyzed for all periods during which mean daily O3 exceeded the 90th percentile concurrently with a maximum 8-h average (MDA8) O3 that was "exceptionally high" for the site (65 ppbv at PAVA, 70 ppbv at ECHO and GBNP), and of potential regulatory significance. An MDA8 ≥ 65 ppbv occurred only five times at PAVA, whereas this occurred on 49 and 65 days at GBNP and ECHO, respectively. The overall correlation between O3 and other pollutants was poor, consistent with the large distance from significant primary emission sources. Mean CO at these locations exceeded concentrations reported for background sites in 2000. Trajectory residence time calculations and air pollutant concentrations indicate that exceedances at GBNP and ECHO were promoted by air masses originating from multiple sources, including wildfires, transport of pollution from southern California and the marine boundary layer, and transport of Asian pollution plumes. Results indicate that the State of Nevada will exceed a revised O3 standard due to sources that are beyond their control.

Gradient measurements of gaseous elemental mercury (Hg0) in the marine boundary layer of the northwest Sea of Japan (East Sea)

Gaseous elemental mercury (Hg⁰) is a prolific and persistent contaminant in the atmosphere. Atmospheric concentrations of Hg⁰ were determined from 17 September to 7 October 2015 in the northwest Sea of Japan aboard the Russian research vessel Professor Gagarinsky. Simultaneous measurements of Hg⁰ concentrations were performed 2 m and 20 m above the sea surface using automatic Hg⁰ analysers RA-915M and RA-915+, respectively. Concentrations ranged from 0.3 to 25.9 ng/m³ (n = 5207) and from 0.3 to 27.8 ng/m³ (n = 4415), with medians of 1.7 and 1.6 ng/m³, respectively. Elevated Hg⁰ was observed during three episodes from 19 to 22 September, likely caused by one or more of the following factors: 1) atmospheric transport of Hg⁰ from the west and south-west (from N. Korea, China, and the Yellow Sea region); 2) Hg⁰ emission from the sea due to pollution by water from the Tumannaya River; or 3) underwater geological activities. Increased Hg⁰ concentration was observed during periods when air masses flowed from the south, and low concentrations were observed when air masses came from the north. A daytime increase of Hg⁰ concentrations at a height of 2 m occurred simultaneously with decreasing Hg⁰ at a height of 20 m. These diurnal variations suggest that two contrasting processes occur during the daytime in the marine boundary layer (MBL): Hg⁰ emission from the sea surface and Hg⁰ oxidation in the MBL by active halogens formed by photolysis.

The trans-continental distributions of pentachlorophenol and pentachloroanisole in pine needles indicate separate origins

The production and use of pentachlorophenol (PCP) was recently prohibited/restricted by the Stockholm Convention on persistent organic pollutants (POPs), but environmental data are few and of varying quality. We here present the first extensive dataset of the continent-wide (Eurasia and Canada) occurrence of PCP and its methylation product pentachloroanisole (PCA) in the environment, specifically in pine needles. The highest concentrations of PCP were found close to expected point sources, while PCA chiefly shows a northern and/or coastal distribution not correlating with PCP distribution. Although long-range transport and environmental methylation of PCP or formation from other precursors cannot be excluded, the distribution patterns suggest that such processes may not be the only source of PCA to remote regions and unknown sources should be sought. We suggest that natural sources, e.g., chlorination of organic matter in Boreal forest soils enhanced by chloride deposition from marine sources, should be investigated as a possible partial explanation of the observed distributions. The results show that neither PCA nor total PCP (ΣPCP = PCP + PCA) should be used to approximate the concentrations of PCP; PCP and PCA must be determined and quantified separately to understand their occurrence and fate in the environment. The background work shows that the accumulation of airborne POPs in plants is a complex process. The variations in life cycles and physiological adaptations have to be taken into account when using plants to evaluate the concentrations of POPs in remote areas.

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.

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.

Measurement of the mixing state of PAHs in individual particles and its effect on PAH transport in urban and remote areas and from major sources

Although recent laboratory simulations have demonstrated that organic matter prevents the degradation of polycyclic aromatic hydrocarbons (PAHs), their role in the long-range transport of PAHs in the real atmosphere remains poorly understood. In this study, we measured the chemical composition and mixing state of PAHs-containing individual particles in aerosols from three sources, one urban area and one remote area. PAHs-containing particles were classified into five types: organic carbon (OC), potassium mixed with organic carbon (KOC), potassium mixed with sodium (KNa), Krich and PAH-rich. The PAH-rich and KOC particles were the main types of particles produced by vehicle exhaust/coal burning and biomass burning, respectively, accounting for >50% of the PAHs-containing particles. It was found that organic matter enhancement of PAHs-containing particles occurs in the ambient atmosphere, with organic-rich (OC and KOC) particles accounting for >90%. Further analysis revealed that the increase in the fractions of PAHs was related to the mixing state with organic compounds due to the protection of organics against PAHs and/or the aging of PAHs-containing particles. The results of this study improve our understanding of the chemical composition and mixing state of PAHs particles in atmospheric aerosols from emission sources and urban and remote areas, and provide field observation evidence to support the promotion of the study of long-range transport of PAHs by organics.

Non-polar organic compounds in marine aerosols over the northern South China Sea: Influence of continental outflow

Filter samples of total suspended particle (TSP) collected during a cruise campaign over the northern South China Sea (SCS) from September to October 2013 were analyzed for non-polar organic compounds (NPOCs) as well as organic carbon (OC), elemental carbon (EC) and water-soluble ions. A total of 115 NPOCs species in groups of n-alkanes, polycyclic aromatic hydrocarbons (PAHs), iso-/antiso-alkanes, hopanes, steranes, methylalkanes, branched alkanes, cycloalkanes, alkenes and phthalates were detected. The characteristics of NPOCs in marine TSP samples were investigated to understand the sources from the Asian continent and other regions. The concentrations of total NPOCs ranged from 19.8 to 288.2 ng/m(3) with an average of 87.9 ng/m(3), which accounted for 0.8-1.7% (average 1.0%) of organic matter (OM). n-Alkanes was the predominant group, accounting for 43.1-79.5%, followed by PAHs (5.5-44.4%) and hopanes (1.6-11.4%). We found that primary combustion (biomass burning/fossil fuel combustion) was the dominant source for the majority of NPOCs (89.1%). Biomass burning in southern/southeastern China via long-range transport was proposed to be a major contributor of NPOCs in marine aerosols over the northern SCS, suggested by the significant correlations between nss-K(+) and NPOCs groups as well as the analysis of air mass back-trajectory and fire spots. For the samples with strong continental influence, the strong enhancement in concentrations of n-alkanes, PAHs, hopanes and steranes were attributed to fossil fuel (coal/petroleum) combustion. In addition, terrestrial plants waxes were another contributor to NPOCs.

Mercury concentrations in breast feathers of three upper trophic level marine predators from the western Aleutian Islands, Alaska

Mercury (Hg) is a toxic element distributed globally through atmospheric transport. Agattu Island, located in the western Aleutian Islands, Alaska, has no history of point-sources of Hg contamination. We provide baseline levels of total mercury (THg) concentrations in breast feathers of three birds that breed on the island. Geometric mean THg concentrations in feathers of fork-tailed storm-petrels (Oceanodroma furcata; 6703 ± 1635, ng/g fresh weight [fw]) were higher than all other species, including snowy owl (Bubo scandiacus; 2105 ± 1631, ng/g fw), a raptor with a diet composed largely of storm-petrels at Agattu Island. There were no significant differences in mean THg concentrations of breast feathers among adult Kittlitz's murrelet (Brachyramphus brevirostris; 1658 ± 1276, ng/g fw) and chicks (1475 ± 671, ng/g fw) and snowy owls. The observed THg concentrations in fork-tailed storm-petrel feathers emphasizes the need for further study of Hg pollution in the western Aleutian Islands.

Persistent organic pollutants in the Antarctic marine environment: The influence impacts of human activity, regulations, and climate change

This study investigates the presence, distribution, and potential impacts of perfluoroalkyl substances (PFASs) and hexabromocyclododecanes (HBCDs) on the Antarctic marine environment. The analysis results from the King Sejong Station, the Jang Bogo Station, and Cape Evans revealed the highest concentrations of both PFASs and HBCDs at King Sejong Station, indicating the significant influence of human activity. Short-chain perfluorocarboxylic acids (PFCAs) dominated the seawater samples, with PFPeA at the highest concentration (0.076 ng/L) at King Sejong Station, whereas perfluorosulfonic acids (PFSAs) were prevalent in the sediments, with PFHxS reaching 0.985 ng/g. Total PFASs in benthos ranged from N.D. to 2.40 ng/g ww across all stations. This indicated the effects of long-range transport and glacial meltwater. α-HBCD was the most common diastereomer in benthos samples, detected in 58.3% of samples, suggesting its selective persistency. Although risk quotient analysis revealed low immediate risks to lower-trophic organisms, potential risks remain owing to their persistence and bioaccumulation potential. Contaminant patterns changed after regulations: perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) levels decreased, unregulated PFASs increased, HBCD stereoisomer ratios shifted towards α-HBCD dominance, and overall HBCD concentrations declined. Widespread persistence of regulated substances was observed in Antarctic environments, highlighting the need for comprehensive and long-term monitoring strategies. This study provides essential baseline data on contaminant distributions across the Southern Ocean, contributing to our understanding of emerging pollutants in Antarctic regions and informing future environmental protection efforts.

Comparison of inorganic nitrogen concentrations in airborne particles at inshore and offshore sites in the Yellow Sea (2017-2019): Long-range transport and potential impact on marine productivity

Atmospheric deposition of nitrogen is one of the most important external nutrient sources. We investigated the concentrations of NO3- and NH4+ in airborne particles at both an offshore and an inshore site in the Yellow Sea. At the offshore site, devoid of local sources and located downwind from the highly developed areas of Korea and China, the concentrations of atmospheric particulate NO3- and NH4+ were ∼88 ± 101 nmol m-3 and ∼102 ± 102 nmol m-3, respectively, likely due to the transboundary long-range transport of pollutants. The inshore site showed a concentration ∼2 times higher than the offshore site. Considering not only dry inorganic nitrogen deposition but also wet and organic material deposition, the total atmospheric nitrogen deposition was estimated to contribute roughly 10 % to the new production in the Yellow Sea.

Decomposing PM2.5 concentrations in urban environments into meaningful factors: 1. Separating the contribution of local anthropogenic activities from background and long-range transport

Fine particulate matter (PM2.5) is a complex mixture of aerosol particles with varying properties and sources, both local and distant. In areas lacking detailed monitoring of PM2.5 speciation, the common source-apportionment analyses are not applicable. This study demonstrates an alternative framework for estimating sources and processes that affect observed PM2.5 concentrations when information on the particle composition is unavailable. Eight years (2012-2019) of half-hourly PM2.5 observations from 10 air quality monitoring (AQM) stations, clustered according to their airmass transport sector were analyzed, using Non-negative Matrix Factorization (NMF). Factors were determined based on their variation in time, space, and between airmass sectors. Employing a supervised machine-learning model provided insights into the relationships between the extracted factors, meteorological parameters and co-measured airborne pollutants. Factor interpretations were evaluated through comparisons with measurements of PM2.5 species from a nearby Surface PARTiculate mAtter Network (SPARTAN) station. The NMF successfully separated background factors from an urban anthropogenic-activity factor, with the latter accounting for approximately 60 % of the observed PM2.5 levels in Tel Aviv (∼10±6μg/m3). Positive monotonic relationships were observed between the PM2.5 urban anthropogenic-activity factor and measurements of nitrogen oxides (NOx) and absolute humidity (AH), representing the impact of traffic emissions and hygroscopic growth, respectively. The summer background factor was found to represent long-range transport (LRT) from Europe, showing a good agreement (R2 = 0.81) with ammonium sulphate concentrations. Our results demonstrate that a spatial NMF analysis can reliably estimate contributions of different sources with distinct compositions and properties to the total observed PM2.5. Using such an analysis, future environmental health studies could assess health risks associated with exposure to distinct PM2.5 fractions. This information may assist decision makers to set environmental targets for abating PM2.5 with specific compositions and properties.

Back-trajectory analyses for evaluating the transboundary transport effect to the aerosol pollution in South Korea

This study performed a back-trajectory analysis to determine the influence of transboundary transport on the extent of aerosol pollution in South Korea, based on 5-year PM2.5 measurements (2015-2019) in five cities covering South Korea. A transboundary transport case was selected if a back trajectory passed over a dedicated region (BOX 1 and BOX 2) in the Yellow Sea. First, we found that the frequency of transboundary transport largely increases in the high pollution case, and this pattern is almost consistent for all months and all five cities, indicating the importance of investigating the horizontal direction of air mass movement associated with PM2.5, which has been discussed extensively in previous studies. In this study, we also examined the altitude change and straight moving distance (defined as travel distance) of back trajectories regarding the extent of local PM2.5. Consequently, we found that back trajectories in high aerosol pollution showed much lower altitudes and shorter travel differences, implying a significant contribution of surface emissions and stagnant air conditions to severe aerosol pollution. As a result, the local PM2.5 level was not significantly enhanced when the air mass passed over the Yellow Sea if transboundary transport occurred at high altitudes with rapid movement (i.e., high altitude and long travel distance back-trajectory). Based on these results, we suggest utilizing the combined information of the horizontal direction, altitude variation, and length of back trajectories to better evaluate transboundary transport.

Air quality and characterization of synoptic circulation weather patterns in a South American city from Argentina

The potential cause-effect relationship between synoptic meteorological conditions and levels of criteria air pollutants, including CO, NO2, O3, PM10, PM2.5 and SO2, in Bahia Blanca, Argentina, was assessed for the period of 2018-2019. Daily back-trajectories and global meteorological data fields were employed to characterize the primary transport paths of air masses reaching the study site, and to identify the synoptic meteorological patterns responsible for these atmospheric circulations. Time series of surface-level meteorological parameters and midday mixing layer height were collected to examine the impact of the synoptic meteorological patterns on local meteorology. Furthermore, the NAAPS global aerosol model was utilized to identify days when contributions from long-range transport processes, such as dust and/or biomass burning smoke, impacted air quality. By applying this methodology, it was determined that the air masses coming from the N, NW and W regions significantly contributed to increased mean concentrations of coarse particles in this area through long-range transport events involving dust and smoke. Indeed, the high average levels of PM10 recorded in 2018-2019 (annual mean values of 47 and 52 μg/m3, respectively) represent the main air quality concern in Bahía Blanca. Moreover, PM10, PM2.5 and NO2 emissions should be reduced in order to meet recommended air quality guidelines. On the other hand, the results from this study suggest that the sources and meteorological processes leading to the increase in the concentrations of CO and SO2 have a local-regional origin, although these air pollutants did not reach high values probably as a consequence of the strong wind speed registered in this region during any synoptic meteorological pattern.

Comment on "Optimization of suspect and non-target analytical methods using GC/TOF for prioritization of emerging contaminants in the Arctic environment"

Lee et al. (2019) recently proposed that volatile methylsiloxanes (VMS) be considered as emerging contaminants in the Arctic environment based on the results of suspect and non-target screening of environmental samples collected from Ny-Ålesund, Svalbard. In any analytical program, it is of critical importance to be able to discern if the identification of analytes is due to true presence in the sampled environmental media or if contamination occurred during sample handling and analysis, leading to false positive detection. This is particularly important for VMS due to their ubiquity in consumer products, sample containers, and analytical instrumentation, thus requiring robust quality control (QC) procedures to support the validity of results. Although Lee et al. (2019) concluded that VMS in the environmental samples originated from potential long-range transport and deposition, it is most likely that local point sources account for their presence. Additionally, there is low confidence in the validity of the reported detection of VMS in the sampled environmental media as this study does not include any of the necessary QC to determine whether the VMS detected would be due to contamination or indicative of presence in the environment.