Trends in MODIS and AERONET derived aerosol optical thickness over Northern Europe.

2019 | Tellus B Chem Phys Meteorol | 71 (1) (1-21)

Long-term Aqua and Terra MODIS (MODerate resolution Imaging Spectroradiometer) Collections 5.1 and 6.1 (c051 and c061, respectively) aerosol data have been combined with AERONET (AERosol RObotic NETwork) ground-based sun photometer observations to examine trends in aerosol optical thickness (AOT, at 550 nm) over Northern Europe for the months April to September. For the 1927 and 1559 daily coincident measurements that were obtained for c051 and c061, respectively, MODIS AOT varied by 86 and 90%, respectively, within the predicted uncertainty of one standard deviation of the retrieval over land (ΔAOT = ±0.05 ± 0.15·AOT). For the coastal AERONET site Gustav Dalen Tower (GDT), Sweden, larger deviations were found for MODIS c051 and c061 (79% and 75%, respectively, within predicted uncertainty). The Baltic Sea provides substantially better statistical representation of AOT than the surrounding land areas and therefore favours the investigations of trends in AOT over the region. Negative trends of 1.5% and 1.2% per year in AOT, based on daily averaging, were found for the southwestern Baltic Sea from MODIS c051 and c061, respectively. This is in line with a decrease of 1.2% per year in AOT at the AERONET station Hamburg. For the western Gotland Basin area, Sweden, negative trends of 1.5%, 1.1% and 1.6% per year in AOT have been found for MODIS c051, MODIS c061 and AERONET GDT, respectively. The strongest trend of –1.8% per year in AOT was found for AERONET Belsk, Poland, which can be compared to –1.5% per day obtained from MODIS c051 over central Poland. The trends in MODIS and AERONET AOT are nearly all statistically significant at the 95% confidence level. The strongest aerosol sources are suggested to be located southwest, south and southeast of the investigation area, although the highest prevalence of pollution events is associated with air mass transport from southwest.

Remobilization of old permafrost carbon to Chukchi Sea sediments during the end of the last deglaciation

Jannik Martens; Birgit Wild; Christof Pearce; Tommaso Tesi; August Andersson; Lisa Bröder; Matt O'Regan; Martin Jakobsson; Martin Sköld; Laura Gemery; Thomas M. Cronin; Igor Semiletov; Oleg V. Dudarev; Örjan Gustafsson
2019 | Global Biogeochem Cycles | 33

Climate warming is expected to destabilize permafrost carbon (PF‐C) by thaw‐erosion and deepening of the seasonally thawed active layer and thereby promote PF‐C mineralization to CO2 and CH4. A similar PF‐C remobilization might have contributed to the increase in atmospheric CO2 during deglacial warming after the last glacial maximum. Using carbon isotopes and terrestrial biomarkers (Δ14C, δ13C, and lignin phenols), this study quantifies deposition of terrestrial carbon originating from permafrost in sediments from the Chukchi Sea (core SWERUS‐L2‐4‐PC1). The sediment core reconstructs remobilization of permafrost carbon during the late Allerød warm period starting at 13,000 cal years before present (BP), the Younger Dryas, and the early Holocene warming until 11,000 cal years BP and compares this period with the late Holocene, from 3,650 years BP until present. Dual‐carbon‐isotope‐based source apportionment demonstrates that Ice Complex Deposit—ice‐ and carbon‐rich permafrost from the late Pleistocene (also referred to as Yedoma)—was the dominant source of organic carbon (66 ± 8%; mean ± standard deviation) to sediments during the end of the deglaciation, with fluxes more than twice as high (8.0 ± 4.6 g·m−2·year−1) as in the late Holocene (3.1 ± 1.0 g·m−2·year−1). These results are consistent with late deglacial PF‐C remobilization observed in a Laptev Sea record, yet in contrast with PF‐C sources, which at that location were dominated by active layer material from the Lena River watershed. Release of dormant PF‐C from erosion of coastal permafrost during the end of the last deglaciation indicates vulnerability of Ice Complex Deposit in response to future warming and sea level changes.

A Multi-Pollutant Air Quality Health Index (AQHI) Based on Short-Term Respiratory Effects in Stockholm, Sweden

Olstrup, H.; Johansson, C.; Forsberg, B.; Tornevi, A.; Ekebom, A.; Meister, K.
2019 | Int J Environ Res Public Health | 16 (1) (105-129)

In this study, an Air Quality Health Index (AQHI) for Stockholm is introduced as a tool to capture the combined effects associated with multi-pollutant exposure. Public information regarding the expected health risks associated with current or forecasted concentrations of pollutants and pollen can be very useful for sensitive persons when planning their outdoor activities. For interventions, it can also be important to know the contribution from pollen and the specific air pollutants, judged to cause the risk. The AQHI is based on an epidemiological analysis of asthma emergency department visits (AEDV) and urban background concentrations of NOx, O3, PM10 and birch pollen in Stockholm during 2001–2005. This analysis showed per 10 µg·m–3 increase in the mean of same day and yesterday an increase in AEDV of 0.5% (95% CI: −1.2–2.2), 0.3% (95% CI: −1.4–2.0) and 2.5% (95% CI: 0.3–4.8) for NOx, O3 and PM10, respectively. For birch pollen, the AEDV increased with 0.26% (95% CI: 0.18–0.34) for 10 pollen grains·m–3. In comparison with the coefficients in a meta-analysis, the mean values of the coefficients obtained in Stockholm are smaller. The mean value of the risk increase associated with PM10 is somewhat smaller than the mean value of the meta-coefficient, while for O3, it is less than one fifth of the meta-coefficient. We have not found any meta-coefficient using NOx as an indicator of AEDV, but compared to the mean value associated with NO2, our value of NOx is less than half as large. The AQHI is expressed as the predicted percentage increase in AEDV without any threshold level. When comparing the relative contribution of each pollutant to the total AQHI, based on monthly averages concentrations during the period 2015–2017, there is a tangible pattern. The AQHI increase associated with NOx exhibits a relatively even distribution throughout the year, but with a clear decrease during the summer months due to less traffic. O3 contributes to an increase in AQHI during the spring. For PM10, there is a significant increase during early spring associated with increased suspension of road dust. For birch pollen, there is a remarkable peak during the late spring and early summer during the flowering period. Based on monthly averages, the total AQHI during 2015–2017 varies between 4 and 9%, but with a peak value of almost 16% during the birch pollen season in the spring 2016. Based on daily mean values, the most important risk contribution during the study period is from PM10 with 3.1%, followed by O3 with 2.0%.

Chemicals of emerging Arctic concern: Preface.

de Wit, C.A.; Balmer, J.; Muir, D.C.G.; Vorkamp, K.; Wilson, S.
2019 | Emerging Contaminants | 5 (1-3)

Molecular-level understanding of synergistic effects in sulfuric acid–amine–ammonia mixed clusters

Myllys, N.; Chee, S.; Olenius, T.; Lawler, M.; Smith, J. N.;
2019 | JOURNAL OF PHYSICAL CHEMISTRY A | 123 (2420-2425)

Understanding atmospheric aerosol particles with improved particle identification and quantification by single-particle mass spectrometry

Shen, XL; Saathoff, H; Huang, W; Mohr, C; Ramisetty, R; Leisner, T
2019 | Atmos. Meas. Tech. | 12 (4) (2219-2240)
ambient aerosols , biomass-burning aerosols , chemical composition , detection efficiencies , effective density , ion formation mechanism , isoprene-derived organosulfates , laser desorption/ionization , mixing state , secondary organic aerosol
Single-particle mass spectrometry (SPMS) is a widely used tool to determine chemical composition and mixing state of aerosol particles in the atmosphere. During a 6-week field campaign in summer 2016 at a rural site in the upper Rhine valley, near the city of Karlsruhe in southwest Germany, similar to 3.7 x 10(5) single particles were analysed using a laser ablation aerosol particle time-of-flight mass spectrometer (LAAPTOF). Combining fuzzy classification, marker peaks, typical peak ratios, and laboratory-based reference spectra, seven major particle classes were identified. With the precise particle identification and well-characterized laboratory-derived overall detection efficiency (ODE) for this instrument, particle similarity can be transferred into corrected number and mass fractions without the need of a reference instrument in the field. Considering the entire measurement period, aged-biomass-burning and soil-dust-like particles dominated the particle number (45.0% number fraction) and mass (31.8% mass fraction); sodium-salt-like particles were the second lowest in number (3.4 %) but the second dominating class in terms of particle mass (30.1 %). This difference demonstrates the crucial role of particle number counts' correction for mass quantification using SPMS data. Using corrections for size-resolved and chemically resolved ODE, the total mass of the particles measured by LAAPTOF accounts for 23 %-68% of the total mass measured by an aerosol mass spectrometer (AMS) depending on the measurement periods. These two mass spectrometers show a good correlation (Pearson's correlation coefficient gamma > 0.6) regarding total mass for more than 85% of the measurement time, indicating non-refractory species measured by AMS may originate from particles consisting of internally mixed non-refractory and refractory components. In addition, specific relationships of LAAPTOF ion intensities and AMS mass concentrations for non-refractory compounds were found for specific measurement periods, especially for the fraction of org / (org + nitrate). Furthermore, our approach allows the non-refractory compounds measured by AMS to be assigned to different particle classes. Overall AMS nitrate mainly arose from sodium-salt-like particles, while aged-biomass-burning particles were dominant during events with high organic aerosol particle concentrations.

Chemical Characterization of Highly Functionalized Organonitrates Contributing to Night-Time Organic Aerosol Mass Loadings and Particle Growth

Huang, W; Saathoff, H; Shen, XL; Ramisetty, R; Leisner, T; Mohr, C
2019 | Environ. Sci. Technol. | 53 (3) (1165-1174)
air pollution , alpha-pinene , isoprene , Mountain site , nox , oxidation , soa formation , spectrometer , united-states , volatility
Reactions of volatile organic compounds (VOC) with NO3 radicals and of reactive intermediates of oxidized VOC with NO can lead to the formation of highly functionalized organonitrates (ON). We present quantitative and chemical information on ON contributing to high nighttime organic aerosol (OA) mass concentrations measured during July-August 2016 in a rural area in southwest Germany. A filter inlet for gases and aerosols coupled to a high-resolution time-of-flight chemical ionization mass spectrometer (FIGAERO-HR-ToF-CIMS) was used to analyze the molecular composition of ON in both the gas and particle phase. We find larger contributions of ON to OA mass during the night. Identified ON are highly functionalized, with 4 to 12 oxygen atoms. The diel patterns of ON compounds with 5, 7, 10, or 15 carbon atoms per molecule vary, indicating a corresponding behavior of their potential precursor VOC. The temporal behavior of ON after sunset correlates with that of the number concentration of ultrafine particles, indicating a potential role of ON in night-time new particle formation (NPF) regularly observed at this location. We estimate an ON contribution of 18-25% to the mass increase of newly formed particles after sunset. Our study provides insights into the chemical composition of highly functionalized ON in the rural atmosphere and the role of anthropogenic emissions for night-time SOA formation in an area where biogenic VOC emissions dominate.

Insights into the O : C-dependent mechanisms controlling the evaporation of alpha-pinene secondary organic aerosol particles

Buchholz, A; Lambe, AT; Ylisirnio, A; Li, ZJ; Tikkanen, OP; Faiola, C; Kari, E; Hao, LQ; Luoma, O; Huang, W; Mohr, C; Worsnop, DR; Nizkorodov, SA; Yli-Juuti, T; Schobesberger, S; Virtanen, A
2019 | Atmos. Chem. Phys. | 19 (6) (4061-4073)
absorption-model , gas , high-resolution , isothermal dilution , kinetics , mass-spectrometer , oxidation , phase , thermodenuder , volatility basis-set
The volatility of oxidation products of volatile organic compounds (VOCs) in the atmosphere is a key factor to determine if they partition into the particle phase contributing to secondary organic aerosol (SOA) mass. Thus, linking volatility and measured particle composition will provide insights into SOA formation and its fate in the atmosphere. We produced alpha-pinene SOA with three different oxidation levels (characterized by average oxygen-to-carbon ratio; (O:C) over bar = 0.53, 0.69, and 0.96) in an oxidation flow reactor. We investigated the particle volatility by isothermal evaporation in clean air as a function of relative humidity (RH < 2 %, 40 %, and 80 %) and used a filter-based thermal desorption method to gain volatility and chemical composition information. We observed reduced particle evaporation for particles with increasing <(O:C )over bar> ratio, indicating that particles become more resilient to evaporation with oxidative aging. Particle evaporation was increased in the presence of water vapour and presumably particulate water; at the same time the resistance of the residual particles to thermal desorption was increased as well. For SOA with (O:C ) over bar = 0.96, the unexpectedly large increase in mean thermal desorption temperature and changes in the thermogram shapes under wet conditions (80 % RH) were an indication of aqueous phase chemistry. For the lower (O:C ) over bar cases, some water-induced composition changes were observed. However, the enhanced evaporation under wet conditions could be explained by the reduction in particle viscosity from the semi-solid to liquid-like range, and the observed higher desorption temperature of the residual particles is a direct consequence of the increased removal of high-volatility and the continued presence of low-volatility compounds.

Gas to Particle Partitioning of Organic Acids in the Boreal Atmosphere

Lutz, A; Mohr, C; Le Breton, M; Lopez-Hilfiker, FD; Priestley, M; Thornton, JA; Hallquist, M
2019 | ACS EARTH AND SPACE CHEMISTRY | 3 (7) (1279-1287)
Gas to particle partitioning of carboxylic acids was investigated using a high-resolution chemical ionization time-of-flight mass spectrometer (HR-CI-ToF-MS) with the filter inlet for gases and aerosol (FIGAERO). Specifically, the partitioning coefficients of 640 components with unique molecular composition were calculated from an assumed linear relationship between [particle]/[gas] versus the mass of the organic fraction (M-org) according to Raoult's law, i.e., equilibrium phase partitioning. We demonstrate that, using the full data set, most of the compounds do not follow a linear relationship. This is especially the case for low- and high-molecular-weight species. Using a subset of the data, with concurrent low sulfate ambient observations ([SO42- < 0.4 mu g m(-3)), the relationship improved significantly and K-i could be derived from the slope of a linear regression to the data. The 100 species with the highest R-2 (>= 0.7) of this regression are presented. The restrictions during high sulfate conditions can be explained by changes in either the equilibrium conditions (e.g., the activity coeffient, gamma(i)) or uptake kinetics (mass transfer limitation). This study demonstrates that partitioning of compounds in the complex ambient atmosphere follows ideal Raoult's law for some limited conditions and stresses the need for studies also in more polluted environments.

Highly Oxygenated Organic Molecules (HOM) from Gas-Phase Autoxidation Involving Peroxy Radicals: A Key Contributor to Atmospheric Aerosol

Bianchi, F; Kurten, T; Riva, M; Mohr, C; Rissanen, MP; Roldin, P; Berndt, T; Crounse, JD; Wennberg, PO; Mentel, TF; Wildt, J; Junninen, H; Jokinen, T; Kulmala, M; Worsnop, DR; Thornton, JA; Donahue, N; Kjaergaard, HG; Ehn, M
2019 | Chem. Rev. | 119 (6) (3472-3509)
alpha-pinene ozonolysis , chemical-ionization , ionization mass-spectrometer , multifunctional compounds , nucleation mode particles , oxidized ro2 radicals , pure component properties , saturation vapor-pressures , sulfuric acid , volatility basis-set
Highly oxygenated organic molecules (HOM) are formed in the atmosphere via autoxidation involving peroxy radicals arising from volatile organic compounds (VOC). HOM condense on pre-existing particles and can be involved in new particle formation. HOM thus contribute to the formation of secondary organic aerosol (SOA), a significant and ubiquitous component of atmospheric aerosol known to affect the Earths radiation balance. HOM were discovered only very recently, but the interest in these compounds has grown rapidly. In this Review, we define HOM and describe the currently available techniques for their identification/quantification, followed by a summary of the current knowledge on their formation mechanisms and physicochemical properties. A main aim is to provide a common frame for the currently quite fragmented literature on HOM studies. Finally, we highlight the existing gaps in our understanding and suggest directions for future HOM research.

Role of base strength, cluster structure and charge in sulfuric-acid-driven particle formation

Myllys, N.; Kubečka, J.; Besel, V.; Alfaouri, D.; Olenius, T.; Smith, J. N.; Passananti, M.;
2019 | Atmos. Chem. Phys. | 19 (9753-9768)

Influence of Hydrodynamic Processes on the Fate of Sedimentary Organic Matter on Continental Margins

Bao R., van der Voort T., Zhao M., Guo X., Montluçon D., McIntyre C., Eglinton T.,
2018 | Global Biogeochem Cycles
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