Atmospheric Environment

The impact of wildfires on particulate carbon in the western U.S.A Publication date: 15 September 2019 Source: Atmospheric Environment, Volume 213 Author(s): Weeberb J. Requia, Brent A. Coull, Petros Koutrakis Abstract Most of the previous investigations on the relationship between PM2.5 chemical characteristics and wildfire focused on the predictions of particle components concentrations or future pollution scenarios. Little research has focused on trends analyses based on large temporal datasets. Our research addresses this gap by quantifying the long-term impacts of wildfires on ambient particulate carbon levels (organic carbon - OC and elemental carbon - EC) in the western U.S. over a long of 29 years (1988–2016). We quantified the past wildfire-related increases in EC and OC concentration using Generalized Additive Models (GAMs). We used a framework that derives "penalties" (wildfire penalty, in μg/m3 per year) for each season (warm and cold) by accounting for the differences of the β values between two models – adjusted (wildfire included as covariate in the model) and unadjusted model (wildfire is removed from the model). While the wildfire impact is incorporated into the unadjusted trends, the control by wildfire in the adjusted model removes the impact of inter-annual wildfire variation on EC and OC trends. Therefore, we considered that any differences between the unadjusted and wildfire-adjusted trends are entirely attributable to the impact of long-term wildfire changes. A positive penalty (βunadjusted> βadjusted) suggests that an increase in EC and OC is associated with long-term wildfire changes between 1988 and 2016. Wildfires increased in the warm season and decreased in the cold season. We estimated an annual increase of 20.106 km2 of area burned (95% CI: 20.103; 20.109) in the warm period. EC and OC concentrations increased during the warm and cold season. EC and OC concentrations had an annual decrease of 0.03 μg/m3 (95% CI: −0.14; 0.08) and 0.10 μg/m3 (95% CI: −0.21; 0.01), respectively. In the cold period, our analyses showed an increase of 0.05 μg/m3 (95% CI: −0.07; 0.17) and 0.07 μg/m3 (95% CI: −0.04; 0.19) per year for EC and OC, respectively. In the warm season, during the study period (1988–2016), the estimated total concentration change (total penalty) for EC was 0.003 μg/m3 (95%CI: 0.001 and 0.005) and for OC was 0.015 μg/m3 (95%CI: 0.008 and 0.022). In the cold season the penalties were statistically insignificant.

Observation-based estimates of the mass absorption cross-section of black and brown carbon and their contribution to aerosol light absorption in East Asia Publication date: 1 September 2019 Source: Atmospheric Environment, Volume 212 Author(s): Chaeyoon Cho, Sang-Woo Kim, Meehye Lee, Saehee Lim, Wenzheng Fang, Örjan Gustafsson, August Andersson, Rokjin J. Park, Patrick J. Sheridan Abstract In this study, we estimated the contribution of black carbon (BC) and brown carbon (BrC) to aerosol light absorption from surface in-situ and aerosol robotic network (AERONET) columnar observations. The mass absorption cross-section (MAC) of BC (MACBC) was estimated to be 6.4 ± 1.5 m2 g−1 at 565 nm from in-situ aerosol measurements at Gosan Climate Observatory (GCO), Korea, in January 2014, which was lower than those observed in polluted urban areas. A BrC MAC of 0.62 ± 0.06 m2 g−1 (565 nm) in our estimate is approximately ten times lower than MACBC at 565 nm. The contribution of BC and BrC to the carbonaceous aerosol absorption coefficient at 565 nm from the in-situ measurements was estimated at 88.1 ± 7.4% and 11.9 ± 7.4%, respectively at GCO. Similarly, the contribution of BC and BrC to the absorption aerosol optical depth (AAOD) for carbonaceous aerosol (CA), constrained by AERONET observations at 14 sites over East Asia by using different spectral dependences of the absorption (i.e., absorption Ångström exponent) of BC and BrC, was 84.9 ± 2.8% and 15.1 ± 2.8% at 565 nm, respectively. The contribution of BC to CA AAOD was greater in urban sites than in the background areas, whereas the contribution of BrC to CA AAOD was higher in background sites. The overall contribution of BC to CA AAOD decreased by 73%–87% at 365 nm, and increased to 93%–97% at 860 nm. The contribution of BrC to CA AAOD decreased significantly with increasing wavelength from approximately 17% at 365 nm to 4% at 860 nm.

Extreme levels and chemistry of PM from the consumer fireworks in the Netherlands Publication date: 1 September 2019 Source: Atmospheric Environment, Volume 212 Author(s): Harry ten Brink, René Otjes, Ernie Weijers Abstract Mass concentrations of Particulate Matter (PM) in New-Year's nights can be high in the Netherlands because of the unconstrained use of consumer fireworks. In the study presented here the chemical compounds of the PM were determined. It is for the first time that this information was used to deduced the average composition of the explosive mixture/black powder. Measurements were made during the turn of the year 2007–2008 at an urban background location, when hourly PM10 mass concentrations exceeded 2000 μg m−3 at street sites. These extreme levels were due to the stagnant weather conditions occurring that night. The on-line artefact-free "MARGA" was deployed for assessment of the major compounds. These were found to be the (hygroscopic) salts KCl, MgSO4 and K2SO4. The mass ratio of sulphur and potassium showed that a standard black powder mix is used as explosive. The potassium was for 65% present as KCl. This is the reduction product of the oxidiser KClO4, which is hence the main oxidiser. The rest of the potassium was present in the form of K2SO4. We proved that this compound derives from the "standard" oxidiser KNO3 of black powder. The formation of the SO42--salts is explained as follows. The sulphur in the black powder oxidises to H2SO4. This compound reacts with the reduction product of the KNO3 to K2SO4. MgSO4 forms in a reaction of the main colouring agent magnesium with the H2SO4. The full composition of the PM, including carbonaceous material and trace metals, was obtained from an analysis of 24-hr filter samples. This showed that the mentioned salts comprised about half of the mass, while almost all of the remainder is "carbon" deriving from the incomplete combustion of the cardboard wrapping. About 85% of the PM10 is in the more harmful PM2.5.

Ozone dose-response relationships for soil microbial dynamics of winter wheat in North China Publication date: 1 September 2019 Source: Atmospheric Environment, Volume 212 Author(s): Enzhu Hu, Ruinan Dong, Xiangli Nan, Zaijian Yuan, Hongxing Zhang, Xiaoke Wang, Weiwei Zhang Abstract Dynamic responses of soil microbial properties of winter wheat (Triticum aestivum L.) to elevated ozone concentration have never been quantified. In this study, the winter wheat was cultivated under two contrasting ozone treatments: non-filtered ambient air (hereinafter called NF) and elevated ozone (effective increase in 9-h mean ozone concentration of 34.91 ± 1.42 nL·L−1 (mean ± SE) above ambient, hereinafter called EO3). Linear regressions between the response ratio of each variable (i.e. EO3/NF) and the increments of exposure- or flux-based ozone indices (i.e. EO3 - NF) were conducted. The results showed that the response ratios of soil microbial biomass C and N, as well as cumulative CO2 and N2O effluxes significantly correlated with the increments of ozone indices. The ΔPOD0 (increment of integrated phytotoxic ozone dose with no threshold) and the ΔAOT40 (increment of accumulated hourly O3 concentrations over a threshold of 40 nL·L−1) performed better than ΔSUM06, ΔW126 and the increments of other flux-based ozone indices. They showed stronger linear relationships with soil microbial biomass than that with gas effluxes. The expanded deviations from the effect-free line indicated distinct cumulative detrimental ozone impacts on soil microbial properties. Ammonia nitrogen content and nitrite reductase activity showed non-significantly adaptive and self-adjustment responses to accumulative ozone stress. The ozone dose-response relationships obtained here will benefit the ecological modeling that evaluates the dynamic responses or predicts the feedback effects of sustainable agro-ecosystems under global climate change.

Activity size distribution of radioactive nuclide 7Be at different locations and under different meteorological conditions Publication date: 1 September 2019 Source: Atmospheric Environment, Volume 212 Author(s): A. Ioannidou, K. Eleftheriadis, M. Gini, L. Gini, S. Manenti, F. Groppi Abstract The activity size distributions of the natural radionuclide tracer 7Be in different size fractions (<0.4 μm, 0.4–0.7 μm, 0.7–1.1 μm, 1.1–2.1 μm, 2.1–3.1 μm, 3.1–4.2 μm, 4.2–5.8 μm, 5.8–9.0 μm > 9.0 μm) were determined at four different site places in Northern Italy during the four seasons of the year 2011. One cascade impactor operated at the LASA-station considered the reference station and the other used for simultaneous measurements at the three other sites. Three sets of independent samples were collected during every season of the year 2011. The initial activity distribution inverted into smooth size distribution. The model parameters successfully defined to obtain the best fit-curve and two or three modes were resolved, with the predominant fit at the accumulation range. The lowest Activity Median Aerodynamic Diameter (AMAD) values were observed during summer. The AMAD values were anticorrelated with 7Be activities, while they were correlated with Relative Humidity. Similar AMAD values in suburban and urban regions were observed during all periods of the year. AMAD values of 7Be aerosol particles in areas with poor air quality were greater than those at the less polluted environments far from anthropogenic activities regions. This indicates that 7Be AMAD values could be used as an index of air quality conditions in areas like the Po Valley.

Heterogeneous photochemistry of dicarboxylic acids on mineral dust Publication date: 1 September 2019 Source: Atmospheric Environment, Volume 212 Author(s): Milena Ponczek, Nathalie Hayeck, Corinne Emmelin, Christian George Abstract Dicarboxylic acids have low volatilities and hence are present mostly in the particulate phase, including the surface of dust particles. Mineral dust, globally the most emitted aerosol, has photocatalytic properties that can initiate photo-induced heterogeneous chemistry of organic compounds, which is still poorly characterized. We investigated the photochemistry of five dicarboxylic acids (DCA) i.e., succinic (butanedioic) acid, glutaric (pentanedioic) acid, adipic (hexanedioic) acid, pimelic (heptanedioic) acid and suberic (octanedioic) acid on Arizona test dust (ATD) particles upon UV-A light irradiation (0–1.4 mW cm−2). Gas-phase products were monitored by a high-resolution proton-transfer-reaction mass spectrometer (PTR-ToF-MS), and surface sorbed products were extracted and analyzed by ultra-high-performance liquid chromatography coupled to a heated electrospray ionization high-resolution mass spectrometer (UHPLC-HESI-HRMS). Monoacids and aldehydes were the main observed and quantified gaseous products. In contrast, shorter chain DCA and highly oxygenated products were found at the surface of the dust particles. Interestingly, the photochemistry of these DCAs presented an even-odd alternation concerning their heterogeneous reactivity, with odd-numbered carbon diacids being more reactive than their even-numbered homologous ones. We present and discuss a reaction mechanism for the C4–C8 DCA heterogeneous photooxidation catalysed by TiO2/Fe2O3-rich dust particles. Our results suggest that photochemical processing on dust surfaces should be regarded as a possible efficient pathway for altering their surface properties impacting ice nucleation and cloud condensation properties.

Source apportionment of carbonaceous aerosols in the vicinity of a Mediterranean industrial harbor: A coupled approach based on radiocarbon and molecular tracers Publication date: 1 September 2019 Source: Atmospheric Environment, Volume 212 Author(s): Lise Bonvalot, Thibaut Tuna, Yoann Fagault, Alexandre Sylvestre, BouAlem Mesbah, Henri Wortham, Jean-Luc Jaffrezo, Nicolas Marchand, Edouard Bard Abstract Located in the Mediterranean Basin and close to Marseille (France), Fos-sur-Mer is situated in the vicinity of industrial harbor and agricultural lands. Its location makes it prone to mixed pollution contributions, combining the influence of residential, industrial, agricultural, maritime road and traffic sources. For this study, the origins of carbonaceous particles sampled over several months are investigated by a coupled approach based on analyses of radiocarbon (14C), elemental to total carbon ratio (EC/TC) and various molecular tracers (levoglucosan, methoxyphenols, malic and glyceric acids), giving information about their background origins. Accelerator mass spectrometry with a gas ion source give the opportunity to quantify the fossil and non-fossil fractions for each individual sample, avoiding to pool them. Analyzing 14C in micro-samples (down to a few μg of carbon) complements the approach based on chemical tracers, which are useful to identify sources, but insufficient to quantify accurately the modern and fossil carbon fractions. The measurements in about 30 samples collected during summer and fall/winter 2013, allow the detection of a strong seasonality of the pollution: the fall/winter PM2.5 fraction concentration equals to three times the summer concentration and we observe a significant fluctuation of the relative contributions of fossil and non-fossil fractions (fNF is ≈ 0.83 for fall/winter samples and ≈0.59 for summer samples). Significant correlations between 14C, levoglucosan and different methoxyphenols, allow the identification and quantification of a major influence of biomass burning emissions during fall and winter. Biomass burning organic carbon (OCBB) and elemental carbon (ECBB) contribute to 45% and 8% of the TC, respectively, whereas their total contribution is only 3% in summer samples. Biogenic emissions from the vegetation are the main sources of carbon during summer (≈57%). Significant correlations between summer OCbio and malic acid and DL glyceric acid suggest a secondary origin for this fraction. The total fossil carbon concentration (ECF and OCF) from vehicular, shipping and industrial sources is constant throughout the year, which is compatible with intense road and maritime traffics and industrial activity during both seasons. Overall, our study based on 14C and molecular tracers illustrates the power of a coupled approach in order to both identify and quantify biomass burning, biogenic, traffic and industrial sources of carbonaceous aerosols, forming a complex mix of background PM origins in a typical industrious harbor of the Mediterranean region.

The Ruthenium-106 plume over Europe in 2017: a source-receptor model to estimate the source region Publication date: 1 September 2019 Source: Atmospheric Environment, Volume 212 Author(s): Niccolò Maffezzoli, Giovanni Baccolo, Elena Di Stefano, Massimiliano Clemenza Abstract Between the end of September and the beginning of October 2017, low but detectable air concentrations of Ruthenium-106 (R106u) were measured throughout the European atmosphere. To date, the source has not been clearly identified. This study aims at constraining the location of the most likely emission source, by combining HYSPLIT back trajectories and a multi-site source-receptor model. The model follows a concentration weighted trajectory (CWT) approach, based on a R106u measurement dataset gathered by the International Atomic Energy Agency (IAEA) shortly after the event and shared by the French Institut de Radioprotection et de Sûreté Nucléaire (IRSN). The back trajectories are computed using Global Data Assimilation System (GDAS) and ERA-Interim meteorological data, with horizontal resolution from 1.5° to 0.5°. The effect of the starting altitude was also investigated. The source-receptor model results show that the most likely emission source region extends from Ukraine to the West to the Russian Volga and Ural regions to the East, in accordance with two previous studies. The analyses also show that the identified source region is relatively insensitive to the type of meteorological data, their horizontal resolution and values of starting altitude. The model precision is found to increase with increasing number of receptors. The method is fully open-source, requires low computational resources and is therefore suited to estimate the source origin of radioactive pollutants on a real time basis, providing an additional tool to more sophisticated atmospheric models.

Magnetic characteristics of atmospheric dustfall in a subtropical monsoon climate zone of China and its environmental implications: A case study of Nanjing Publication date: 1 September 2019 Source: Atmospheric Environment, Volume 212 Author(s): Longsheng Wang, Shouyun Hu, Mingming Ma, Yingjun Zhang, Xiaohui Wang, Qing Wang, Zhenhua Zhang, Buli Cui, Xianbin Liu Abstract Nanjing is located in the subtropical monsoon climate zone of China. In this study, a series of monthly collections of atmospheric dustfall was performed in different directions from a high-rise building in Nanjing from February 2015 to March 2016. A series of magnetic parameters including χ, χfd%, χARM, SIRM, magnetic hysteresis loops, high-temperature κ-T curves and SEM images was measured from atmospheric dustfall samples. The research shows that the type and size of magnetic minerals within atmospheric dustfall samples in Nanjing are similar to those found in northern cities in China, but the atmospheric dustfall samples in Nanjing have higher magnetic mineral concentrations. Coarse-grained magnetite dominated magnetic minerals. The peak concentrations of magnetic minerals contained from atmospheric dustfall of Nanjing occurred in summer. The relationship between magnetic parameters and meteorological data shows that the high values are mainly influenced by precipitation rather than by wind direction. Combined with results of the SEM images and the weak relationship between magnetic parameters and the data of PM 2.5 and PM10, all these indicate that the atmospheric dustfall of Nanjing is mainly from near-source polluted dustfall rather than from long-distance dustfall. This research suggests that environmental magnetism as a simple, economic and nondestructive technology, will be a useful tool in atmospheric dustfall research.

Precipitation chemistry and deposition at a high-elevation site in the Pacific Northwest United States (1989–2015) Publication date: 1 September 2019 Source: Atmospheric Environment, Volume 212 Author(s): Anne M. Johansen, Clint Duncan, Ashleen Reddy, Naomi Swain, Mari Sorey, Annika Nieber, James Agren, Matt Lenington, David Bolstad, Barbara Samora, Rebecca Lofgren Abstract Emissions from fuel combustion and agricultural activities contribute significantly to the continuous atmospheric entrainment of pollutants into protected and vulnerable ecosystems where long-term monitoring is often a challenge. Here, results are presented from a 26-year study (1989–2015) of wet precipitation collected at Paradise Station (1654 m above sea level), Mount Rainier National Park, Washington, USA. Weekly samples were analyzed for pH, conductivity and major anions and cations. While precipitation concentrations for sulfate, nitrate, protons and conductivity peaked in the early 2000s, overall trends decreased by 54%, 46%, 41%, and 37%, respectively. Associated pH values increased from 5.2 to 5.6, and were largely controlled by non-sea-salt contributions of sulfate and neutralizing calcium, potassium and magnesium. Between 1999 and 2015, nitrogen (N) deposition rates from ammonium increased by a factor of 3.6, from 0.27 to 0.96 kg N ha−1 yr−1 (p = 0.02), while nitrate deposition did not change statistically (0.91–0.74 kg N ha−1 yr−1, p = 0.30). Combined, these N sources are reaching reported critical loads of 2.0 kg N ha−1 yr−1. Results indicate that emission regulations focused on stationary sources have effectively decreased apparent acid precipitation, however, increased nitrogen deposition from ammonium may lead to further fertilization and acidification of delicate soils and waters. Continued long-term monitoring is thus imperative to track continued anthropogenic inputs to vulnerable ecosystems.

Alexandros Sfakianakis
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alsfakia@gmail.com