Winter Campaign Research Articles

Enhanced New Particle Formation Above the Marine Boundary Layer Over the Yellow Sea: Potential Impacts on Cloud Condensation Nuclei

AbstractAircraft measurements of aerosols were conducted over the Yellow Sea and the East China Sea from February 14 to March 10, 2013, during the Aerosol Radiative Forcing in East Asia 2013 Winter campaign. Ground‐based measurements of aerosols were also conducted on Fukue Island (32.8°N, 128.7°E), located near the boundary of the Yellow Sea and the East China Sea. The aircraft measurements revealed large increases in particle number concentrations in the nucleation mode (2.5–10 nm and up to ~105 cm−3) at altitudes of ~0.5–3 km over the Yellow Sea. This was attributed to enhanced new particle formation (NPF) above the marine boundary layer over the Yellow Sea. The number ratios of Aitken‐mode (10–90 nm) or accumulation‐mode (>90 nm) particles to black carbon particles (tracer for primary emissions) were used to quantify the effects of NPF on particle number concentrations. We estimated that NPF increased median Aitken‐mode particle number concentrations by an order of magnitude at altitudes of ~1–3 km over the Yellow Sea. Synchronized aircraft and ground‐based data suggest that vertical transport of Aitken‐mode particles formed over the Yellow Sea led to a large variability in the particle growth events observed on Fukue Island. A shift of sea surface temperature near Fukue Island and the resultant promotion of vertical mixing are probably the key mechanisms responsible for this complex feature. Evolution of accumulation‐mode particles was observed farther downwind over the East China Sea, suggesting significant impacts of NPF on the regional distributions of cloud condensation nuclei.

Sources and Potential Health Risks of PM2.5-Bound PAHs in a Megacity of Southwest China: Importance of Studying from a Health Risk Perspective

PM2.5-bound polycyclic aromatic hydrocarbons (PAHs) with adverse effect on human and ecosystem health is of concern worldwide. In this study, they were measured in summer and winter at an urban site in Chongqing, a megacity of southwest China to investigate their potential sources, to evaluate the inhalation cancer risks and to identify the dominant source responsible for health risk. The mean concentration of total PAHs was 9.67 ± 2.53 ng/m3 in summer, much lower than that in winter (49.6 ± 16.5 ng/m3). The source apportionment method of Positive Matrix Factorization combined with diagnostic ratios was successfully applied in this study and identified coal combustion and vehicle emission (contributing to 56% of the total PAHs mass), biomass burning (21%) and volatilization (23%) as the potential sources of PM2.5-bound PAHs in Chongqing. Regional transport from southern and southeastern regions have contributed to the elevated PM2.5-bound PAHs in summer while local and nearby areas acted as main source regions in winter mainly due to the specific topographic and meteorological conditions in Chongqing. Daily Benzo[a]pyrene equivalent (BaPeq) concentrations (2.47–17.9 ng/m3) during 97% of the winter campaign exceeded the National Ambient Air Quality Standard (2.5 ng/m3). Furthermore, the lifetime cancer risk (LCR) values denoted a high potential cancer risk in winter, especially during aerosol pollution period. The contribution from the mixed source of coal combustion and vehicle emission (64%) to LCR was higher than that to the mass concentration while that of biomass burning (13%) was lower, which may result from the emission of higher toxic compounds from the mixed source. Elevated contribution from the mixed source was observed in winter especially during pollution days, indicating the significance of controlling the sources with high health risks. The results in this study call for the attention to the source apportionment from a health risk perspective.

Online Chemical Characterization and Source Identification of Summer and Winter Aerosols in Măgurele, Romania

Aerosols and organic source apportionment were characterized using data collected during two measurement campaigns. These campaigns were conducted during the summer and winter seasons at Măgurele, a site located southwest of Bucharest, the capital of Romania and one of the largest cities in southeastern Europe (raking seven in Europe based on population). The summer campaign was conducted between 7 June–18 July 2012, and the winter campaign from 14 January–6 February 2013. Approximately 50% of the organic fraction contribution to the total submicron particulate matter sampled by aerosol mass spectrometer was evidenced during both seasons. Submicronic organic aerosol sources were quantified using the positive matrix factorization approach. For warm (summer) and cold (winter) seasons, more than 50% from total organics was represented by oxidized factors. For the summer season, separate analyses were conducted on data influenced by urban and non-urban sources. The influence of pollution from Bucharest on the measurement site was observed in aerosol concentration and composition. The primary organic aerosols have different contribution percentage during summer, depending on their main origin. The influence of Bucharest, during summer, included cooking contribution of 13%. The periods with more regional influence were characterized by lower contribution from traffic and biomass burning in a total proportion of 28%. In winter, the influence of local non-traffic sources was dominant. For more than 99% of the measurements, the biomass burning indicator, f 60 , exceeded the background value, with residential heating being an important source in this area. Fossil fuel contribution was confirmed for one week during the winter campaign, when 14 C analysis of total and elemental carbon revealed the presence of 17% fossil contributions to total carbon. Mass spectrometry, 14 C and absorption data suggest biomass burning as the predominant primary source of organic aerosols for the winter season.

Source Contributions to Rural Carbonaceous Winter Aerosol in North-Eastern Poland

Concentrations of aerosol particles in Poland and their sources are rarely discussed in peer-reviewed journal articles despite serious air quality issues. A source apportionment of carbonaceous aerosol particles was performed during winter at a rural background environment field site in north-eastern Poland. Data were used of light absorption at seven wavelengths and levoglucosan concentrations along existing monitoring of PM2.5, organic carbon and elemental carbon (OC/EC) at the Diabła Góra EMEP monitoring site between January 17 and March 19 during the EMEP intensive winter campaign of 2018. Average PM2.5, OC, EC, equivalent black carbon (eBC) and levoglucosan concentrations and standard deviations amounted to 18.5 ± 9.3, 4.5 ± 2.5, 0.57 ± 0.28, 1.04 ± 0.62 and 0.134 ± 0.084 µg m−3 respectively. Various tools for source apportionment were used to obtain a source contribution to carbonaceous matter (CM) with three components. The wood combustion source component contributed 1.63 µg m−3 (21%), domestic coal combustion 3.3 µg m−3 (41%) and road transport exhaust 2.9 µg m−3 (38%). Similar levels and temporal variability were found for the nearby Lithuanian site of Preila, corroborating the Polish results.

Investigating the regional contributions to air pollution in Beijing: a dispersion modelling study using CO as a tracer

Abstract. The rapid urbanization and industrialization of northern China in recent decades has resulted in poor air quality in major cities like Beijing. Transport of air pollution plays a key role in determining the relative influence of local emissions and regional contributions to observed air pollution. In this paper, dispersion modelling (Numerical Atmospheric Modelling Environment, NAME model) is used with emission inventories and in situ ground measurement data to track the pathways of air masses arriving in Beijing. The percentage of time the air masses spent over specific regions during their travel to Beijing is used to assess the effects of regional meteorology on carbon monoxide (CO), a good tracer of anthropogenic emissions. The NAME model is used with the MEIC (Multi-resolution Emission Inventory for China) emission inventories to determine the amount of pollution that is transported to Beijing from the immediate surrounding areas and regions further away. This approach captures the magnitude and variability of CO over Beijing and reveals that CO is strongly driven by transport processes. This study provides a more detailed understanding of relative contributions to air pollution in Beijing under different regional airflow conditions. Approximately 45 % over a 4-year average (2013–2016) of the total CO pollution that affects Beijing is transported from other regions, and about half of this contribution comes from beyond the Hebei and Tianjin regions that immediately surround Beijing. The industrial sector is the dominant emission source from the surrounding regions and contributes over 20 % of the total CO in Beijing. Finally, using PM2.5 to determine high-pollution days, three pollution classification types of pollution were identified and used to analyse the APHH winter campaign and the 4-year period. The results can inform targeted control measures to be implemented by Beijing and the surrounding provinces to tackle air quality problems that affect Beijing and China.

Land use drives nitrous oxide dynamics in estuaries on regional and global scales

AbstractUrban and agricultural development of coastal catchments is known to increase dissolved nitrogen inputs into estuaries; however, much less is known about how land use influences the production of the powerful greenhouse gas nitrous oxide (N2O). Here, we assess dissolved N2O dynamics in four nearby estuaries across a regional land use gradient and summarize the literature to put the observations into global perspective. During summer dry conditions, N2O saturation ranged from 131.4% ± 45.0% in the most pristine system (28% modified) to 198.6% ± 52.3% within the most modified urban system (91% modified). The N2O saturation in the wetter winter campaign was higher and more variable than the summer dry campaign (range 84.7–677.7%) likely due to direct transport of N2O into the estuaries from catchment runoff and/or produced through denitrification fueled by high nitrate inputs. During both seasons, N2O was lowest in areas adjacent to fringing mangroves and highest in upstream fresh/saltwater mixing areas. Coupling our results with previously published N2O data from 50 estuarine systems worldwide revealed that estuarine N2O increases concomitantly with catchment modification, dissolved inorganic nitrogen availability, and decreasing oxygen concentrations. Based on these results, a 1% increase in anthropogenic modification to global catchments (i.e., agricultural development and/or urbanization) may increase estuarine N2O saturation by 2.6% ± 1.2%. These findings indicate that future estuarine N2O emissions are likely to increase as anthropogenic modification of coastal catchments intensifies.

Rawinsonde‐Based Analysis of the Urban Boundary Layer in the Metropolitan Region of São Paulo, Brazil

AbstractThe main features of the urban boundary layer in the metropolitan region of São Paulo are estimated based on rawinsondes carried out (a) every 3 hr in two 10‐day field campaigns of the MCITY BRAZIL Project during the summer and winter of 2013 and (b) regularly once per day and continuously for 4 years from 2009 to 2013. On average, the boundary layer height showed a daytime maximum of 1476 ± 149 m in summer and 1122 ± 168 m in winter campaigns. The differences are related to seasonal variations in the (a) buoyancy flux at the surface, which was 30% larger in summer (4.7 ± 0.6 MJ m−2 day−1), and the (b) static stability of the free atmosphere, which was 15% smaller in summer (3.3 ± 0.1 K km−1). The average nighttime boundary layer height, estimated from equilibrium empirical expression, indicated maximum of 126 ± 13 m in summer and 122 ± 10 m in winter campaigns. The presence of a low‐level jet was identified in 80% of the field campaign nights, with intensity varying from 2.7 to 14 m s−1 and height ranging from 95 to 962 m. The nighttime residual‐mixing layer is well estimated using the air temperature gradient method and is a good indication of the maximum vertical evolution of the previous daytime boundary layer. The monthly average maximum boundary layer height varied from a minimum of 1,061 ± 77 m in September to maximum of 1,632 ± 96 m in May.

TRAGEDY IN BAZAR IN THE COMMEMORATIVE PRACTICES OF THE ANTI-BOLSHEVIK INSURGENCY AND UKRAINIAN EMIGRATION IN THE 1920s–1930s

The objective of the article is to investigate the commemorative practices related to the tragedy in Bazar in the context of the anti-Bolshevik insurgency and Ukrainian emigration of the 1920s–1930s. The methodology of the scientific research is based on the general scientific and special historical methods, taking into account the basic principles of historical world perception: historicism, scientific character, objectivity, systematic approach. The principles of historicism and scientific character have made it possible to reproduce the peculiarities of the commemorative practices associated with the tragedy in Bazar in all its complexity and diversity, interrelation and interdependence with the events of the time. The principle of objectivity is a helpful way to analyze the outlined problem with a critical survey of reference data. The principle of the systematic approach has enabled us to form a coherent picture of the manifestations of the commemorative practices in memory of the victims of the tragedy during the outlined period. The scientific novelty of the research lies in the fact that it examines the events of November 1921 from the standpoint of the historical memory schools for the first time. A great variety of reference data has made it possible to examine the commemorative practices in the memory of the victims of the tragedy in Bazar in a short chronological period from the 1920s and during the 1930s. As a result of the study, the author concludes that the first attempts to commemorate the victims at their burial sites occurred in the early 1920s. The preservation of the memory of the tragedy in Bazar fostered the spread of anti-Bolshevik insurgencies in Zhytomyr region. As the Soviet authorities aimed to destroy the historical memory of the victims of the November 1921 execution, the attempts to preserve it through various commemorative practices were connected with the Ukrainian political emigration abroad (Poland, France, and Czechoslovakia) because the former Ukrainian military as well as the emigration government structures of the UNR were situated there. In the interwar period the commemoration of the tragedy in Bazar was embodied and reflected in the works of fine art. Furthermore, memoirs on both the Second Winter Campaign of the UNR Army and the tragedy in Bazar were published during this time.

Spatial and Temporal Variability of Carbonaceous Aerosol Absorption in the Po Valley

Knowledge gaps in the optical properties of carbonaceous aerosols account for a significant fraction of the uncertainty of aerosol - light interactions in climate models. Both black carbon (BC) and brown carbon (BrC) can display a range of optical properties in ambient aerosol due to different sources and chemical transformation pathways. This study investigates the optical absorption properties of BC and BrC at an urban and a rural site in the Po Valley (Italy), a known European pollution hot spot. We observed spatial and seasonal variability of aerosol absorption coefficients, with the highest values measured in winter at the urban site of Milan (12 Mm–1 on average) and the lowest values in summer at the rural site of Motta Visconti (3 Mm–1 on average). The average aerosol Absorption Ångström Exponent (AAE) measured during the two experiments across the 370–880 nm wavelength range was 1.1 and 1.2 at the urban and the rural site, respectively. The observed AAE values in winter (the average AAE during the two winter campaigns was 1.2) are consistent with the contribution of wood burning BrC, as confirmed by macro-tracer analysis. The BC mass absorption cross section (MACBC) did not show a specific seasonal or spatial variability across the two sites and maintained an average value of 10 ± 5 m2 g–1 at 880 nm. The optical properties of BrC, investigated off-line after extraction of organic aerosol (OA) indicate that wood burning was the dominant BrC source in winter, while secondary organic aerosol (SOA) from other anthropogenic emissions was the main source of BrC in summer.

Metal Ion Release from Fine Particulate Matter Sampled in the Po Valley to an Aqueous Solution Mimicking Fog Water: Kinetics and Solubility

ABSTRACT Metals are among the key aerosol components exerting adverse health effects. Their toxic properties may vary depending on their chemical form and solubility, which can be affected by aqueous processing during aerosol atmospheric lifetime. In this work, fine particulate matter (PM2.5) was collected in the city centre of Padua in the Po Valley (Italy), during a winter campaign. Part of the sampling filters were used to measure the kinetics by which metal ions and other elements can leach from PM2.5 to an aqueous solution mimicking fog water in the winter in temperate climate regions (pH 4.7, 5°C). The leaching process was interpreted by a first order kinetics, and the fitting of the experimental data allowed to obtain the leaching kinetic constants and the equilibrium concentrations (i.e., at infinite time) for all elements. The remaining filter parts were mineralised, through two subsequent extraction steps, and the extracts were analysed by ICP-MS to gain the total elemental content of PM for a large number of elements. We found that elements can leach from PM with half times generally between 10–40 minutes, which is a timescale compatible with atmospheric aqueous processing during fog events. For instance, aluminium(III) in PM2.5 dissolved with an average k = 0.0185 min–1, and t1/2 = 37.5 min. Nevertheless, a fraction of each element was immediately solubilised after contact with the extraction solution suggesting that metal ion solubilisation may already had started during particle lifetime in the atmosphere.

Multi-method determination of the below-cloud wet scavenging coefficients of aerosols in Beijing, China

Abstract. Wet scavenging is one of the most efficient processes for removing aerosols from the atmosphere. This process is not well constrained in chemical transport models (CTMs) due to a paucity of localized parameterization regarding the below-cloud wet scavenging coefficient (BWSC). Here we conducted field measurements of the BWSC during the Atmospheric Pollution and Human Health Beijing (APHH-Beijing) campaign of 2016. Notably, the observed BWSC values based on the updated aerosol mass balance agree well with another estimation technique, and they fall in a range of 10−5 s−1. The measurement in this winter campaign, combined with that in summer of 2014, supported an exponential power distribution of BWSCs with rainfall intensity. The observed parameters were also compared with both the theoretical calculations and modeling results. We found that the theoretical estimations can effectively characterize the observed BWSCs of aerosols with sizes smaller than 0.2 µm and larger than 2.5 µm. However, the theoretical estimations were an order of magnitude lower than observed BWSCs within 0.2–2.5 µm, a domain size range of urban aerosols. Such an underestimation of BWSC through a theoretical method has been confirmed not only in APHH-Beijing campaign but also in all the rainfall events in summer of 2014. Since the model calculations usually originated from the theoretical estimations with simplified scheme, the significantly lower BWSC could well explain the underprediction of wet depositions in polluted regions as reported by the Model Inter-Comparison Study for Asia (MICS-Asia) and the global assessment of the Task Force on Hemispheric Transport of Atmospheric Pollutants (TF-HTAP). The findings highlighted that the wet deposition module in the CTMs requires improvement based on field measurement estimation to construct a more reasonable simulation scheme for BWSC, especially in polluted regions.

Profiles of cloud condensation nuclei, dust mass concentration, and ice-nucleating-particle-relevant aerosol properties in the Saharan Air Layer over Barbados from polarization lidar and airborne in situ measurements

Abstract. The present study aims to evaluate lidar retrievals of cloud-relevant aerosol properties by using polarization lidar and coincident airborne in situ measurements in the Saharan Air Layer (SAL) over the Barbados region. Vertical profiles of the number concentration of cloud condensation nuclei (CCN), large particles (diameter d>500 nm), surface area, mass, and ice-nucleating particle (INP) concentration are derived from the lidar measurements and compared with CCN concentrations and the INP-relevant aerosol properties measured in situ with aircraft. The measurements were performed in the framework of the Saharan Aerosol Long-range Transport and Aerosol-Cloud-Interaction Experiment (SALTRACE) in summer 2013. The CCN number concentrations derived from lidar observations were up to a factor of 2 higher than the ones measured in situ aboard the research aircraft Falcon. Possible reasons for the difference are discussed. The number concentration of particles with a dry radius of more than 250 nm and the surface-area concentration obtained from the lidar observations and used as input for the INP parameterizations agreed well (<30 %–50 % deviation) with the aircraft measurements. In a pronounced lofted dust layer during summer (10 July 2013), the lidar retrieval yielded 100–300 CCN per cubic centimeter at 0.2 % water supersaturation and 10–200 INPs per liter at −25 ∘C. Excellent agreement was also obtained in the comparison of mass concentration profiles. During the SALTRACE winter campaign (March 2014), the dust layer from Africa was mixed with smoke particles which dominated the CCN number concentration. This example highlights the unique lidar potential to separate smoke and dust contributions to the CCN reservoir and thus to identify the sensitive role of smoke in trade wind cumuli developments over the tropical Atlantic during the winter season.

Wintertime Variations of Gaseous Atmospheric Constituents in Bucharest Peri-Urban Area

An intensive winter campaign was organized for measuring the surface air pollutants in southeastern Europe. For a three months period, the gas concentrations of NO x , SO 2 , CO, O 3 , and CH 4 as well as meteorological parameters were simultaneously sampled to evaluate the variations and characteristic reactions between the gases during winter at the measuring site. The photochemical production of the ozone was observed through the diurnal variation of ozone and the solar radiation, the maximum concentration for ozone being reached one hour after the maximum value for solar radiation. A non-parametric wind regression method was used to highlight the sources of the air pollutants. The long-range transport of SO 2 and two hotspots for CO from traffic and from residential heating emissions were emphasized. The traffic hotspot situated north of the measuring site, close to the city ring road, is also a hotspot for NO x . The air quality during the cold season was evaluated by comparing the measured gas concentration with the European limits. During the measuring period, the values for NO 2 , CO, and SO 2 concentration were at least two times lower than the European Union pollution limits. Only twice during the study period was the concentration of O 3 higher than the established limits.

Seasonality of Clostridium difficile in the natural environment.

Clostridium difficile is considered the leading cause of antibiotic-associated disease worldwide. In the past decade, a large number of studies have focused on identifying the main sources of contamination in order to elucidate the complete life cycle of the infection. Hospitals, animals and retail foods have been considered as potential vectors. However, the prevalence of C.difficile in these types of samples was found to be rather low, suggesting that other contamination routes must exist. This study explores the presence of C.difficile in the natural environment and the seasonal dynamics of the bacterium. C.difficile was isolated from a total of 45 samples out of 112 collected (40.2%) on 56 sampling points. A total of 17 points were positive only during the winter sampling (30.4%), 10 were positive only during the summer sampling (17.9%) and 9 sampling points (16.1%) were positive in both summer sampling and winter sampling. Spore counts in soil samples ranged between 50 and 250cfu/g for 24.4% of the positive samples, with the highest concentrations detected in samples collected in the forest during winter campaign (200-250cfu/g). A total of 17 different PCR ribotypes were identified, and 15 of them had the genes coding for toxins A and B. Most of those ribotypes had not previously been found or had been isolated only sporadically (<1% of samples) from hospitals in Belgium. Regarding antimicrobial susceptibility, most of the resistant strains were found during the summer campaign. These findings bear out that C.difficile is present in the natural environment, where the bacterium undergoes seasonal variations.

The Fall Speed Variability of Similarly Sized Ice Particle Aggregates

AbstractThe terminal velocity (Vt) of ice hydrometeors is of high importance to atmospheric modeling. Vt is governed by the physical characteristics of a hydrometeor, including mass and projected area, as well as environmental conditions. When liquid hydrometeors coalesce to form larger hydrometeors, the resulting hydrometeor can readily be characterized by its spherical or near-spherical shape. For ice hydrometeors, it is more complicated because of the variability of ice shapes possible in the atmosphere as well as the inherent randomness in the aggregation process, which leads to highly variable characteristics. The abundance of atmospheric processes affecting ice particle dimensional characteristics creates potential for highly variable Vt for ice particles that are predicted or measured to be of the “same size.” In this article we explore the variability of ice hydrometeor Vt both theoretically and through the use of experimental observations. Theoretically, the variability in Vt is investigated by analyzing the microphysical characteristics of randomly aggregated hexagonal shapes. The modeled dimensional characteristics are then compared to aircraft probe measurements to constrain the variability in atmospheric ice hydrometeor Vt. Results show that the spread in Vt can be represented with Gaussian distributions relative to a mean. Variability expressed as the full width at half maximum of the normalized Gaussian probability distribution function is around 20%, with somewhat higher values associated with larger particle sizes and warmer temperatures. Field campaigns where mostly convective clouds were sampled displayed low variability, while Arctic and midlatitude winter campaigns showed broader Vt spectra.

Modeling of aerosol property evolution during winter haze episodes over a megacity cluster in northern China: roles of regional transport and heterogeneous reactions of SO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;

Abstract. Regional transport and heterogeneous reactions have been shown to play crucial roles in haze formation over a megacity cluster centered on Beijing. In this study, the updated Nested Air Quality Prediction Model System (NAQPMS) and the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model were employed to investigate the evolution of aerosols – in terms of the number concentration, size distribution, and degree of aging – in Beijing during six haze episodes between 15 November and 15 December 2016, as part of the Air Pollution and Human Health–Beijing (APHH-Beijing) winter campaign of 2016. The model exhibited reasonable performance not only with respect to mass concentrations of PM2.5 and its components in Beijing but also regarding the number concentration, size distribution, and degree of aging. We revealed that regional transport played a non-negligible role in haze episodes, with contributions of 14 %–31 % to the surface PM2.5 mass concentration. The contribution of regional transport to secondary inorganic aerosols was larger than that to primary aerosols (30 %–63 % and 3 %–12 %, respectively). The chemical transformation of SO2 along the transport pathway from source regions to Beijing was the major source of SO42-. We also found that sulfate formed outside Beijing from SO2 emitted in Beijing; this sulfate was then blown back to Beijing and considerably influenced haze formation. Along the transport pathway, aerosols underwent aging, which altered the mass ratio of the coating of black carbon to black carbon (RBC) and the size distribution of number concentrations. During the episodes, the geometric mean diameter (GMD) increased from less than 100 nm at the initial site to approximately 120 nm at the final site (Beijing), and the RBC increased from 2–4 to 4–8. During haze episodes with high humidity, the average contributions of gas and aqueous chemistry, heterogeneous chemistry, and primary emission to sulfate were comparable. However, their relative contributions varied with pollution levels. Primary emissions had the greatest impact under light to moderate pollution levels, whereas heterogeneous chemistry had a stronger effect under high pollution levels.

Influence of water depth and season on the photodegradation of micropollutants in a free-water surface constructed wetland receiving treated wastewater

Micropollutants such as pharmaceutical products and pesticides are still present in treated wastewater. Several of these compounds are photoactive, either by direct or indirect photodegradation. An innovative on-site experimental protocol was designed to investigate the contribution of photodegradation processes to eliminate micropolluants in constructed wetland (CW). The solar photodegradation of 23 organic micropollutants was studied using in situ photoreactors at different depths. A CW-photodegradation model was designed and calibrated to further scrutinize the contribution of direct and indirect photodegradation processes in the elimination of micropollutants.The results show that photodegradation is most effective in the first 10 cm of the water column. A classification of micropollutants in 3 groups was developed to characterize their photodegradation. A significant increase of the half-life by direct photodegradation was observed in winter compared to summer due to a lower light intensity in winter. On the opposite, for direct + indirect photodegradation, no significant difference was observed between seasons. The decrease in light intensity in winter was compensated by higher nitrates concentration which promoted the formation of hydroxyl radicals and increased indirect photodegradation.The CW-photodegradation model successfully simulated the measured concentrations for direct and indirect photodegradation for 23 micropolluants. Nonetheless, it overestimated the indirect photodegradation with hydroxyl radicals when using default parameter values derived for surface waters. Hence, the consumption of hydroxyl radicals was increased by a factor of 20 for treated water. This model highlighted the predominance of direct photodegradation in the elimination of all micropollutants, except sotalol for the winter campaign.

Bursts of Auroral-Hiss VLF Emissions on the Earth’s Surface at L ~ 5.5 and Geomagnetic Disturbances

We have studied the geomagnetic conditions during the occurrence of auroral-hiss VLF emissions on the Earth’s surface in the form of noise bursts at frequencies above 5–6 kHz. The study is based on an analysis of auroral-hiss observations at auroral latitudes in northern Finland at Kannuslehto station (KAN, L ~ 5.5) during the winter campaigns of 2013–2018. It is shown that auroral-hiss bursts are most often observed in the interval of 20–01 MLT under low geomagnetic activity (Kp < 3). It has been found that the bursts are typical for the growth phase of a magnetospheric substorm; the bursts cease abruptly at the onset of the substorm (the break-up of auroras), which is apparently due to a drastic increase in the absorption of VLF waves in the ionosphere. The bursts are often accompanied by the generation of geomagnetic Pi2 pulsations. VLF observations have shown that auroral-hiss bursts are not observed on the Earth’s surface in the main phase of magnetic storms; however, they are typical of the recovery phase. It has been found from model data that, during the occurrence of auroral hiss, KAN station is usually projected to the near-equatorial region of the auroral oval or to the zone of diffuse precipitation of more energetic electrons, i.e., to lower latitudes than the typical position of visible auroras during that time.

Characterization of black carbon-containing fine particles in Beijing during wintertime

Abstract. Refractory black carbon (BC) is a product of incomplete combustion of fossil fuel, biomass and biofuel, etc. By mixing with other species, BC can play significant roles in climate change, visibility impairment and human health. Such BC-containing particles in densely populated megacities like Beijing may have specific sources and properties that are important to haze formation and air quality. In this work, we exclusively characterized the BC-containing particles in urban Beijing by using a laser-only Aerodyne soot particle aerosol mass spectrometer (SP-AMS), as part of the Atmospheric Pollution &amp;amp; Human Health (APHH) 2016 winter campaign. The average mass ratio of coating to BC core (RBC) was found to be ∼5.0. Positive matrix factorization shows the presence of significant primary fossil fuel and biomass-burning organics (64 % of total organics). Yet secondary species, including sulfate, nitrate and oxygenated organic aerosol (OA) species, could have significant impacts on the properties of BC-containing particles, especially for ones with larger BC core sizes and thicker coatings. Analyses of sources and diurnal cycles of organic coating reveal significant afternoon photochemical production of secondary OA (SOA), as well as nighttime aqueous production of a portion of highly oxygenated OA. Besides SOA, photochemical production of nitrate, not sulfate, appeared to be important. Further investigations on BC-containing particles during different periods show that, on average, more polluted periods would have more contributions from secondary species and more thickly coated BC tended to associate with more secondary species, indicating the important role of chemical aging to the pollution of BC-containing particles in urban Beijing during wintertime. However, for individual pollution events, primary species (fossil fuel, coal and biomass-burning emissions) could also play a dominant role, as revealed by the compositions of BC-containing particles in two polluted episodes during the sampling period.

Urban vegetation and particle air pollution: Experimental campaigns in a traffic hotspot

This work presents the main results of two experimental campaigns carried out in summer and winter seasons in a complex pollution hotspot near a large park, El Retiro, in Madrid (Spain). These campaigns were aimed at understanding the microscale spatio-temporal variation of ambient concentration levels in areas with high pollution values to obtain data to validate models on the effect of urban trees on particulate matter concentrations.Two different measuring approaches have been used. The first one was static, with instruments continuously characterizing the meteorological variables and the particulate matter concentration outside and inside the park. During the summer campaign, the particulate matter concentration was clearly influenced by a Saharan dust outbreak during the period 23 June to 10 July 2016, when most of the particulate matter was in the fraction PM2.5-10. During the winter campaign, the mass concentrations were related to the meteorological conditions and the high atmospheric stability.The second approach was a dynamic case with mobile measurements by portable instruments. During the summer campaign, a DustTrak instrument was used to measure PM10 and PM2.5 in different transects close to and inside the park at different distances from the traffic lane. It was observed a decrease in the concentrations up to 25% at 20 m and 50% at 200 m. High PM10 values were linked to dust resuspension caused by recreational activities and to a Saharan dust outbreak. The highest PM values were measured at the Independencia square, an area with many bus stops and high traffic density. During the winter campaign, three microaethalometers were used for Black Carbon measurement. Both pollutants also showed a reduction in their concentrations when moving towards inside the park. For PM10 and PM2.5, reductions up to 50% were observed, while for BC this reduction was smaller, about 20%.