Contribution Of Long-range Transport Research Articles

The Long-Term Monitoring of Atmospheric Polychlorinated Dibenzo-p-Dioxin Dibenzofurans at a Background Station in Taiwan during Biomass Burning Seasons in El Niño and La Niña Events

To measure the long-range transport of PCDD/Fs, a background sampling site at Mt. Lulin station (Taiwan) was selected based on meteorological information and its location relative to burning events in Southeast Asia. During regular sampling periods, a higher concentration of PCDD/Fs was recorded in 2008 at Mt. Lulin station during La Niña events, with levels reaching 390 fg I-TEQ/m3. In contrast, a higher concentration of 483 fg I-TEQ/m3 was observed in 2013 during biomass burning events. This indicates that La Niña affects the ambient PCDD/F concentrations. The ratio of ΣPCDD/ΣPCDF was 0.59, suggesting significant long-range transport contributions from 2007 to 2023. From 2007 to 2015, the predominant species was 2,3,4,7,8-PCDF, accounting for 25.3 to 39.6% of the total PCDD/Fs. From 2018 onward, 1,2,3,7,8-PCDD became more dominant, accounting for 15.0 to 27.1%. According to the results from the receptor model PMF (n = 150), the sources of PCDD/Fs were identified as dust storms and monsoon events (19.3%), anthropogenic activity (28.5%), and biomass burning events (52.2%). The PSCF values higher than 0.7 highlighted potential PCDD/F emission source regions for Mt. Lulin during biomass burning events, indicating high PSCF values in southern Thailand, Cambodia, and southern Vietnam.

Measurement report: Atmospheric ice nuclei in the Changbai Mountains (2623 m a.s.l.) in northeastern Asia

Abstract. Atmospheric ice nucleation plays an important role in modulating the global hydrological cycle and atmospheric radiation balance. To date, few comprehensive field observations of ice nuclei have been carried out at high-altitude sites, which are close to the height of mixed-phase cloud formation. In this study, we measured the concentration of ice-nucleating particles (INPs) in the immersion freezing mode at the summit of the Changbai Mountains (2623 m above sea level), northeast Asia, in summer 2021. The cumulative number concentration of INPs varied from 1.6 × 10−3 to 78.3 L−1 over the temperature range of −5.5 to −29.0 °C. Proteinaceous-based biological materials accounted for the majority of INPs, with the proportion of biological INPs (bio-INPs) exceeding 67 % across the entire freezing-temperature range, with this proportion even exceeding 90 % above −13.0 °C. At freezing temperatures ranging from −11.0 to −8.0 °C, bio-INPs were found to significantly correlate with wind speed (r = 0.5–0.8, p < 0.05) and Ca2+ (r = 0.6–0.9), and good but not significant correlation was found with isoprene (r = 0.6–0.7) and its oxidation products (isoprene × O3) (r = 0.7), suggesting that biological aerosols may attach to or mix with soil dust and contribute to INPs. During the daytime, bio-INPs showed a positive correlation with the planetary boundary layer (PBL) height at freezing temperatures ranging from −22.0 to −19.5 °C (r > 0.7, p < 0.05), with the valley breezes from southern mountainous regions also influencing the concentration of INPs. Moreover, the long-distance transport of air mass from the Japan Sea and South Korea significantly contributed to the high concentrations of bio-INPs. Our study emphasizes the important role of biological sources of INPs in the high-altitude atmosphere of northeastern Asia and the significant contribution of long-range transport to the INP concentrations in this region.

Assessment of vertical characterization and potential sources of aerosols in different altitude layers: Combined application of MAX-DOAS observation and the 3D-CWT model

Vertical distribution is essential for understanding the regional transport sources of pollutants accumulated at different altitudes. We investigate aerosol extinction coefficient (AEC) profiles based on ground-based multi-Axis differential optical absorption spectroscopy measurements from August 2020 to June 2021 in Ningbo, East China. AEC vertical structures can be classified into three groups: decreasing with height (51.2%), well-mixed (2.4%), and inverse structures (46.4%), which can be explained by long-range transport, the planetary boundary layer heigh, and temperature inversion. Except in the winter, the vertical profile of the AEC typically extends to higher altitudes, which suggests the accumulation, secondary formation, or long-range transport of aerosols at higher altitudes. The three-dimensional concentration weighted trajectory (3D-CWT) model is utilized to elucidate not only altitudinal atmospheric layers in which aerosol transport occurs, but also the potential source areas of aerosols at multiple air mass arrival altitudes. The 3D-CWT model results indicate the long-range transport of aerosols, mainly through backward air mass trajectories within layers 1 (0–500 m) and 2 (500–1000 m). The potential source areas of aerosols at lower altitudes are mainly distributed in the North China Plain. At air mass arrival altitudes exceeding 600 m, the sources likely to affect aerosols in Ningbo are both land-sourced and marine-sourced (including the East China Sea, Yellow Sea, and the marginal sea between Korea and Japan) air flows. At different air mass arrival altitudes, the estimated contributions of long-range transport to aerosols are approximately 6% (200 m), 11% (600 m), and 18% (1000 m). Our findings provide a scientific basis for revealing different aerosol vertical structures and assessing long-range transport contributions in coastal urban areas.

Concentration of Trace Elements in Cryoconites of Mountain and Polar Regions of the World

The surface of mountain glaciers is a place of accumulation of various biogenic organomineral and mineral compounds. As a result of intensive mass deglaciation of glaciers due to climate change and anthropogenic activity, this material can significantly affect the transformation of the landscape in the periglacial zone. Thus, this work considers the contamination of the surface of the Arctic, Antarctic, and Caucasian glaciers by priority pollutants. Atomic absorption spectroscopy was used to analyze trace elements (Cu, Zn, Ni, Cd, Pb) from cryoconite deposits. It was revealed that the cryoconite dust on the Ray-Iz glacier (Polar Urals) has a high level of nickel contamination, which comes to the glacier from local rock materials as a result of their weathering. The lowest concentrations of trace elements are found in one of the Arctic plots located at Mushketov and Aldegonda glaciers, the Caucasus, and the Antarctic, which is due to their relatively low content in the composition of rocks and the relatively low contribution of long-range transport of matter to the polar regions. Contamination of moraine sediments in the periglacial zone can make a significant contribution to the formation of the soil cover of these territories, the pollution of water bodies near the glacier, as well as affect the quality of life of the people living in the immediate vicinity of the mountain areas.

Investigation of the concentration ratios of anthropogenic metal elements in fresh snow at mountain area as a tracer for the discrimination between short- and long-range transport contributions.

Atmospheric deposition of anthropogenic aerosols, which is concerned about several targets of SDGs, was investigated in Japan. Concentrations of trace metal elements (V, Ni, Cd, and Pb), which are index of source for fossil fuel combustion, in winter wet deposition (fresh snow) in mountain area were determined. Average concentrations of snow samples were 0.338 ± 0.289μg L-1 for V, 0.409 ± 0.724μg L-1 for Ni, 0.109 ± 0.110μg L-1 for Cd, and 1.77 ± 1.81μg L-1 for Pbμg L-1. No significant correlations between V and Ni were found for snow samples at remote mountains. A significant correlation between Cd and Pb was observed when the back trajectories of air mass deriving snowfall passed through Northeast China and Huabei. Significant correlations between V and Pb were found in mountains when the air mass passed through Northeast China and Huabei. Changes in normalized concentrations of trace metal elements in snow at the same snowfall event indicated contributions from short-range transportation in suburb area. The metal element concentration ratios were shown to be useful tracers for discrimination between short- and long-range contributions of anthropogenic elements in snow.

Characterization of columnar aerosol over a background site in Central Asia

Ground-based observational characterization of atmosphere aerosols over Central Asia is very limited. This study investigated the columnar aerosol characteristics over Issyk-Kul, Kyrgyzstan, a background site in Central Asia using the long-term (∼14 years: August 2007–November 2021) data acquired with the Cimel sunphotometer. The mean aerosol optical depth (AOD) and Ångström exponent (AE) during the observation period were 0.14 ± 0.10 and 1.19 ± 0.41, respectively. Both AOD and AE varied across seasons, with highest AOD in spring (0.17 ± 0.17). Regarding the aerosol types, clean continental aerosols were dominant type (65%), followed by mixed aerosols (∼19%), clean marine aerosols (∼14%), dust (0.8%), and urban/industrial and biomass burning aerosol (0.7%). The aerosol volume size distribution was bimodal indicating the influence of both anthropogenic and natural aerosols with clear dominance of coarse mode during the spring season. Mainly dust and mixed aerosols were present during high aerosol episodes while the coarse mode aerosol volume concentration was 7.5 (strong episodes) and ∼19 (extreme episodes) times higher than the whole period average. Aerosol over this background sites were from local and regional sources with some contribution of long-range transport.

Drivers of air pollution variability during second wave of COVID-19 in Delhi, India

To curb the 2nd wave of COVID-19 disease in April–May 2021, a night curfew followed by full lockdown was imposed over the National Capital Territory, Delhi. We have analyzed the observed variation in pollutants and meteorology, and role of local and transboundary emission sources during night-curfew and lockdown, as compared to pre-lockdown period and identical periods of 2020 lockdown as well as of 2018 and 2019. In 2021, concentration of pollutants (except O₃, SO₂, and toluene) declined by 4–16% during night-curfew as compared to the pre-lockdown period but these changes are not statistically significant. During lockdown in 2021, various pollutants decreased by 1–28% as compared to the night-curfew (except O₃ and PM₂.₅), but increased by 31–129% compared to the identical period of 2020 lockdown except O₃. Advection of pollutants from the region of moderate lockdown restrictions and an abrupt increase in crop-residue burning activity (120–587%) over Haryana and Punjab increased the air pollution levels over NCT during the lockdown period of 2021 as compared to 2020 in addition to a significant contribution of long-range transport. The increase in PM₂.₅ during the lockdown period of 2021 compared to 2020 might led to 5–29 additional premature mortalities.

A wide-ranging investigation of the COVID-19 lockdown effects on the atmospheric composition in various Italian urban sites (AER – LOCUS)

A widE-Ranging investigation of the first COVID-19 LOCkdown effects on the atmospheric composition in five Italian Urban Sites (AER–LOCUS) has been carried out and is presented in this study. The analysis uses particle and gas concentrations from surface in situ sampling, column aerosol and gas properties from photometer/spectrometers, and satellite NO2 determinations at five sites distributed over the whole Italian territory: Aosta, Milan, Bologna, Rome, and Taranto. These data are related to meteorological conditions to identify the numerous events of long-range transport and separate local from remote influences. Four different types of long-range transport over Italy are identified during the lockdown period, affecting PM10, PM2.5, and NO2 concentrations, and aerosol optical depths: fires plumes from Eastern Europe and Montenegro, dust from the Caspian area and from the Sahara, and pollution from the Po Valley. Once the long-range transport events are identified and excluded, the variation of gas and particle concentrations occurring during the containment period is calculated with respect to the period 2015–2019. A general decrease of PM10 (ranging from a maximum of −52% in Aosta to a minimum of −4% in Taranto), PM2.5 (from −46% in Aosta and Milan to −0.6% in Bologna), BC (from −77% in Aosta to −25% in Milan), NO2 (from −72% in Rome to −4% in Taranto), and benzene (about −50%) concentration is found. A positive variation of PM2.5 is conversely found during March in the southern sites due to some stagnation events, and a strong increase of benzene (up to +104%) in the industrial area of Taranto. Ozone is found to increase by an average of about 30% in all sites. The removal of the long-range transport contributions affects the variations with respect to the reference period reducing the concentrations by up to 22% for PM10 and 29% for PM2.5 in the northern sites, and 18% for PM10 and 16% for PM2.5 in the southern sites. For NO2 the reduction due to the removal is up to 14% in Milan and 6% in the southern sites, while for the aerosol optical depth it is up to 70% in Aosta and 50% in Rome.

Quantifying variability, source, and transport of CO in the urban areas over the Himalayas and Tibetan Plateau

Abstract. Atmospheric pollutants over the Himalayas and Tibetan Plateau (HTP) have potential implications for accelerating the melting of glaciers, damaging air quality, water sources and grasslands, and threatening climate on regional and global scales. Improved knowledge of the variabilities, sources, drivers and transport pathways of atmospheric pollutants over the HTP is significant for regulatory and control purposes. In this study, we quantify the variability, source, and transport of CO in the urban areas over the HTP by using in situ measurement, GEOS-Chem model tagged CO simulation, and the analysis of meteorological fields. Diurnal, seasonal, and interannual variabilities of CO over the HTP are investigated with ∼ 6 years (January 2015 to July 2020) of surface CO measurements in eight cities over the HTP. Annual mean of surface CO volume mixing ratio (VMR) over the HTP varied over 318.3 ± 71.6 to 901.6 ± 472.2 ppbv, and a large seasonal cycle was observed with high levels of CO in the late autumn to spring and low levels of CO in summer to early autumn. The diurnal cycle is characterized by a bimodal pattern with two maximums in later morning and midnight, respectively. Surface CO VMR from 2015 to 2020 in most cities over the HTP showed negative trends. The IASI satellite observations are for the first time used to assess the performance of the GEOS-Chem model for the specifics of the HTP. The GEOS-Chem simulations tend to underestimate the IASI observations but can capture the measured seasonal cycle of CO total column over the HTP. Distinct dependencies of CO on a short lifetime species of NO2 in almost all cities over the HTP were observed, implying local emissions to be predominant. By turning off the emission inventories within the HTP in GEOS-Chem tagged CO simulation, the relative contribution of long-range transport was evaluated. The results showed that transport ratios of primary anthropogenic source, primary biomass burning (BB) source, and secondary oxidation source to the surface CO VMR over the HTP varied over 35 % to 61 %, 5 % to 21 %, and 30 % to 56 %, respectively. The anthropogenic contribution is dominated by the South Asia and East Asia (SEAS) region throughout the year (58 % to 91 %). The BB contribution is dominated by the SEAS region in spring (25 % to 80 %) and the Africa (AF) region in July–February (30 %–70 %). This study concluded that the main source of CO in urban areas over the HTP is due to local and SEAS anthropogenic and BB emissions and oxidation sources, which differ from the black carbon that is mainly attributed to the BB source from South-East Asia. The decreasing trends in surface CO VMR since 2015 in most cities over the HTP are attributed to the reduction in local and transported CO emissions in recent years.

Use of the PSCF method to analyze the variations of potential sources and transports of NO2, SO2, and HCHO observed by MAX-DOAS in Nanjing, China during 2019

Although the government of Nanjing implemented the more stringent atmospheric control measures during the second half of 2019, compared with the same period in 2018, the air pollution has increased unexpectedly, such as the O3 pollution and the acid rain. In this study, therefore, we performed observations of the vertical structures of the precursors (NO2, SO2, and HCHO) that caused the pollutions in Nanjing using the Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) instrument during the daytime of 2019. The concentration of NO2 was found to be concentrated primarily within 200 m of the surface and decayed sharply with height, although the profiles of SO2 and HCHO could extend to higher altitudes than NO2. Then, the potential source contribution function (PSCF) was used to analyze the source distributions in different atmospheric layers of Nanjing's pollutants during different seasons. The results reveal that the downtown and north of Nanjing with the WPSCF is greater than 0.6 constitute the most important potential source areas. Moreover, potential sources in south-central Jiangsu Province (in the summer and autumn) and east-central Anhui Province (in the winter) are also non-negligible (0.4 < WPSCF < 0.6). The transports of SO2 and HCHO from southeastern Anhui and south-central Jiangsu become stronger in the middle and upper layers (WPSCF > 0.5) than transports in the lower layer (0.3 < WPSCF < 0.5). In terms of altitude, the NO2 (SO2) contribution of long-range transport to the research area in the lower, middle, and upper layers accounted for 13% (20%), 11% (32%), and 8% (45%) of the averaged concentration, respectively. The results indicate that there are the significant SO2 transports from the NW (19.08%) and W (18.64%) orientations, while the most of the NO2 transports are approximately 13% in the lower layer, with the main orientations of W (7.29%) and N (6.40%).

Identification of potential sources of elevated PM2.5-Hg using mercury isotopes during haze events

Atmospheric mercury (Hg) pollution has become a serious problem in megacities. In this study, we applied Hg isotopes together with backward-trajectory receptor models to investigate the potential sources and transport of elevated PM2.5-Hg during two haze events in autumn (Oct. and Nov. in 2014) and winter (Jan. in 2015). Results showed that the sources and transport patterns of PM2.5-Hg during haze are complex for different seasons. In autumn, the dominant sources were local and/or regional anthropogenic emissions from northern China, whereas the long-range transport contribution of biomass burning originated from northeastern China in 2014 and eastern China in 2015. Notably, the biomass burning from northeastern China served as an important contribution to elevated PM2.5-Hg in winter. Our data set also suggested that the Δ200HgPBM values may be due to heterogeneous photoreactions on the particles emitted by coal burning, smelting, and cement production, along with photooxidation from the upper troposphere, and could be used as a potential indicator of particle-bound mercury sources owing to its contribution to the exhibited variability. Hg isotopes, together with meteorological models, could be employed to trace the sources of particle-bound Hg in the atmosphere. This study provides a new way to explore the potential sources of atmospheric particulate mercury and its vectors during haze evolution.

A Comparison Study of Chemical Compositions and Sources of PM1.0 and PM2.5 in Hanoi

We simultaneously collected 85 pairs of 24-h PM1.0 and PM2.5 samples from a new urban area in Hanoi, Vietnam, and analyzed their chemical compositions with particle-induced X-ray emission (PIXE) and ion chromatography (IC) to obtain input data for source apportionment via positive matrix factorization (PMF). Sulfate, ammonium, and black carbon (BC) composed the majority of the mass in both size fractions, and the PMF models clearly differentiated the contribution of long-range transport (LRT) aerosols, which accounted for more than two-thirds of the measured PM-bound sulfate and ammonium concentrations, from those of the six in situ sources, viz., resuspended road dust, primary vehicular emissions, coal fly ash, biomass burning emissions, construction dust, and sea salt. Whereas LRT aerosols, coal fly ash, and primary particulate vehicular emissions mainly occurred in the PM1.0, resuspended road dust and biomass-burning fly ash tended to appear in the PM1.0-2.5; hence, we can characterize the anthropogenic emissions in this area by examining the profile of the PM1.0 rather than the PM2.5. Additionally, air masses with inland trajectories originating in northern China and countries northwest and southwest of Vietnam contained more ammonium, sulfate, and BC than those that passed over the East Sea. Finally, the LRT aerosols exhibited high acidity in the PM1.0 but neutrality in the PM2.5.

The effects of meteorological conditions and long-range transport on PM2.5 levels in Hanoi revealed from multi-site measurement using compact sensors and machine learning approach

Hanoi, the capital of Vietnam, frequently experiences heavy air pollution episodes in the winter, causing health concerns for the 7.5 million people living there. Spatial-temporal variations in PM2.5 levels can provide useful information about the sources and transportation of PM2.5. However, the published spatial-temporal data in the area are limited. In this research, PM2.5 concentrations at two sites in Hanoi and a site in Thai Nguyen (60 km north of Hanoi) were observed from October 2017 to April 2018, using newly available low-cost sensors. Hourly concentrations of PM2.5 at the three sites were similar on average (57.5, 54.9, and 53.6 μg m−3) and clearly co-varied, suggesting remarkable large-scale effects. The contribution of long-range transport and meteorological factors on PM2.5 levels were investigated with a machine learning technique based on a random forest (RF) algorithm and concentration weight trajectory (CWT). The results showed that the contribution of long-range transport from the north and northeast to local PM2.5 levels was significant. Moreover, weather normalized PM2.5 concentrations and partial plots of meteorological factors on the levels of PM2.5 showed that meteorological conditions play a significant role in the formation of winter haze events.

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. PM2.5 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 PM2.5 concentrations were estimated for each PM concentration category. The contribution of LRT to PM2.5 concentrations was estimated to be 33% during 2015-2018. When high concentrations of PM2.5 were observed in Seoul, they were likely to be associated with LRT events.

Analysis of surface ozone episodes using WRF-HYSPLIT model at Biga Peninsula in the Marmara region of Turkey

Ozone episodes were observed frequently in Biga Peninsula of Marmara region in Turkey which is suburban site and has forests and agricultural areas. This study aims to understand the role of atmospheric conditions that lead to the ozone episodes over the Biga Peninsula. Ozone concentrations were measured at the monitoring stations for three years (2013–2015) to identify and characterize the ozone episodes in the study area. HYSPLITv4 model driven by the WRF ARW v3.8 and surface data is used to identify the emission source locations. The WRF ARW results were analyzed for the meteorological variables used in the study (e.g. air temperature, relative humidity, u and v wind components) with index of agreement, correlation coefficient, mean bias error, and root mean squared error. It is found that local photochemical production and accumulation and transport of pollutants from the anthropogenic sources (residential, traffic and industrial) in Marmara regions are the most important factors on ozone levels. The five ozone episodes were also analyzed using HYSPLIT model to infer long range transport. Three-day backward air mass trajectories analysis is performed to assess the contribution of long-range transport of pollutants, resulting in the following main routes: Istanbul and Black Sea. The results show that rural areas have higher cumulative exposure to ozone than suburban locations.

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 (PM10S) and mountaintop (PM10M) 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 PM10S 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 PM10S for daytime LRT cases can be explained by the combined effects of increased local emissions and LRT aerosols.

Sources, distribution, and risk assessment of organochlorine pesticides in Nairobi City, Kenya

The distribution and sources of organochlorine pesticides (OCPs) in air and surface waters were monitored in Nairobi City using triolein-filled semipermeable membrane devices (SPMDs). The SPMDs were extracted by dialysis using n-hexane, followed by cleanup by adsorption chromatography on silica gel cartridges. Sample analysis was done by GC-ECD and confirmed by GC–MS. Separation of means was achieved by analysis of variance, followed by pair-wise comparison using the t-test (p≤ 0.05). The total OCPs ranged between 0.018 – 1.277 ng/m3 in the air and <LOD – 1391.000 ng/m3 in surface waters. Based on the results, the means of Industrial Area, Dandora and Kibera were not significantly different (p≤ 0.05), but were higher (p≤ 0.05) than those of City square and Ngong’ Forest. The results revealed non-significant (p≤ 0.05) contribution of long-range transport to OCP pollution in Nairobi City. This indicated possible presence of point sources of environmental OCPs in the city. The water-air fugacity ratios indicated that volatilization and deposition played an important role in the spatial distribution of OCPs in Nairobi City. This indicated that contaminated surface waters could be major sources of human exposure to OCPs, through volatilization. The incremental lifetime cancer risks (ILCR) determined from inhalation of atmospheric OCPs were 2.3745 × 10−13 – 1.6845 × 10−11 (adult) and 5.5404 × 10−13 – 3.9306 × 10−11 (child) in the order: Dandora > Kibera > Industrial Area > City Square > Ngong’ Forest. However, these were lower than the USEPA acceptable risks, 10−6 – 10−4. This study concluded that atmospheric OCPs did not pose significant cancer risks to the residents.

Synoptic circulation patterns and local sources associated to high concentrations of tropospheric ozone in rural and suburban areas in southwestern Spain

In Extremadura, Southwest Spain, environmental conditions combined with a complex mixture of natural and anthropogenic precursors favour the appearance of episodes of high concentrations of tropospheric ozone, whose levels sometimes exceed legal thresholds. In this mainly rural region, no study has been carried out to identify and interpret regional ozone episodes, so this work aims to fill this gap. Ozone and precursor (nitrogen oxides and organic compounds) levels from six representative air quality monitoring stations located in suburban and rural areas have been used to investigate selected ozone episodes during 2014 and 2015. Air mass back-trajectories were used to assess the contribution of long-range transport, resulting in Europe, Mediterranean and Peninsular routes. The analysis of synoptic patterns revealed that high pressures with stationary character, which occur in different synoptic conditions, have an important role in the increment of the ozone values. Finally, the evaluation of the results showed that the daily ozone cycle is mainly regulated by the emissions of precursors in the surrounding environment, the high temperatures that occur during the day and the influence of atmospheric conditions on the low troposphere under anticyclonic conditions that promote ozone accumulation.

Seasonal and annual changes in PAH concentrations in a remote site in the Pacific Ocean

This paper reports the long term observation of particle-associated polycyclic aromatic hydrocarbons (PAHs) at Cape Hedo Atmosphere and Aerosol Monitoring Station, a remote site in the Western Pacific Ocean, from 2008 to 2015. This is the first long-term study that evaluated the contribution of long-range transport of PAHs in East Asia. No obvious trend (P > 0.05) was found in a particular season over the years. However, there are seasonal variations of PAH concentrations with higher in spring and winter. The higher PAH are attributed to air masses from the area including part of China. Source apportionment using three different approaches, i.e., PAH compositional pattern analysis, PAH diagnostic ratio analysis and positive matrix factorization modeling, showed the combined high contribution of biomass burning (18%, 14%) and coal combustion (33%, 24%) in spring and winter. In addition, the contribution of ship emissions (35%) was relatively high in spring, whereas that of vehicle emissions (36%) was relatively high in winter. The contribution of coal combustion to PAH has decreased throughout the years, likely due to changes in energy structure in China. The contribution of biomass burning to PAH has showed no trend, being stable, and that of vehicular emissions has increased.

Long-range transport impacts on surface aerosol concentrations and the contributions to haze events in China: an HTAP2 multi-model study

Abstract. Haze has been severely affecting the densely populated areas in China recently. While many of the efforts have been devoted to investigating the impact of local anthropogenic emission, limited attention has been paid to the contribution from long-range transport. In this study, we apply simulations from six participating models supplied through the Task Force on Hemispheric Transport of Air Pollution phase 2 (HTAP2) exercise to investigate the long-range transport impact of Europe (EUR) and Russia–Belarus–Ukraine (RBU) on the surface air quality in eastern Asia (EAS), with special focus on their contributions during the haze episodes in China. The impact of 20 % anthropogenic emission perturbation from the source region is extrapolated by a factor of 5 to estimate the full impact. We find that the full impacts from EUR and RBU are 0.99 µg m−3 (3.1 %) and 1.32 µg m−3 (4.1 %) during haze episodes, while the annual averaged full impacts are only 0.35 µg m−3 (1.7 %) and 0.53 µg m−3 (2.6 %). By estimating the aerosol response within and above the planetary boundary layer (PBL), we find that long-range transport from EUR within the PBL contributes to 22–38 % of the total column density of aerosol response in EAS. Comparison with the HTAP phase 1 (HTAP1) assessment reveals that from 2000 to 2010, the long-range transport from Europe to eastern Asia has decreased significantly by a factor of 2–10 for surface aerosol mass concentration due to the simultaneous emission reduction in source regions and emission increase in the receptor region. We also find the long-range transport from the Europe and RBU regions increases the number of haze events in China by 0.15 % and 0.11 %, and the North China Plain and southeastern China has 1–3 extra haze days (&lt;3 %). This study is the first investigation into the contribution of long-range transport to haze in China with multi-model experiments.