The Roles of the Atmosphere and Ocean in Driving Arctic Warming Due to European Aerosol Reductions

Krishnan, S; Ekman, AML; Hansson, HC; Riipinen, I; Lewinschal, A; Wilcox, LJ; Dallafior, T
2020 | Geophys Res Lett | 47 (7)
Clean air policies can have significant impacts on climate in remote regions. Previous modeling studies have shown that the temperature response to European sulfate aerosol reductions is largest in the Arctic. Here we investigate the atmospheric and ocean roles in driving this enhanced Arctic warming using a set of fully coupled and slab-ocean simulations (specified ocean heat convergence fluxes) with the Norwegian Earth system model (NorESM), under scenarios with high and low European aerosol emissions relative to year 2000. We show that atmospheric processes drive most of the Arctic response. The ocean pathway plays a secondary role inducing small temperature changes mostly in the opposite direction of the atmospheric response. Important modulators of the temperature response patterns are changes in sea ice extent and subsequent turbulent heat flux exchange, suggesting that a proper representation of Arctic sea ice and turbulent changes is key to predicting the Arctic response to midlatitude aerosol forcing. Plain Language Summary Aerosols are liquid or solid particles suspended in air, which may have adverse air quality and health impacts. Sulfate aerosols also have a cooling influence on climate and can mask some of the greenhouse gas-induced global warming. While aerosol emissions are variable in space and time, their impacts are not limited to where they are emitted. In fact, studies using global climate models have shown that changing sulfur dioxide emissions in Europe can have significant impacts on Arctic climate. Here we investigate the roles of changes in atmospheric and ocean heat transport in driving these changes in the Arctic by conducting a series of climate model simulations with specified anthropogenic sulfur dioxide emissions and different ocean heat transport fluxes. We find that changes through the atmosphere play a primary role in affecting the Arctic climate. These changes are modulated by changes in sea ice extent and the energy exchange between ocean and atmosphere in the sub-Arctic. Aerosol-driven changes in ocean heat transport play a smaller, secondary role in the Arctic and tend to reduce the impacts. Our results show that the proper representation of Arctic sea ice is crucial for accurately modeling the Arctic response to changes in midlatitude aerosol forcing.

Intact Ether Lipids in Trench Sediments Related to Archaeal Community and Environmental Conditions in the Deepest Ocean

Xu, YP; Wu, WC; Xiao, WJ; Ge, HM; Wei, YL; Yin, XR; Yao, HM; Lipp, JS; Pan, BB; Hinrichs, KU
2020 | J. Geophys. Res.-Biogeosci. | 125 (7)
ammonia-oxidizing archaea , archaea , biomarker , carbon , challenger deep , diversity , gdgt , hadal zone , intact polar lipid , mass spectrometry , membrane-lipids , organic-matter , oxygen , polar lipids , tetraether lipids , tex86
Archaea play an important role in marine biogeochemical cycle; however, their phylogenetic distribution and lipid composition in the hadal zone (6-11 km water depth) are poorly known. Here, we analyzed archaeal membrane lipids and 16S rRNA gene sequences in sediments from Mariana Trench (MT), Massau Trench (MS), and New Britain Trench (NBT), varying from 1,560 to 10,840 m depth. Forty-two intact polar lipids (IPLs) were identified, including glycerol dialkyl glycerol tetraethers (GDGTs), OH-GDGTs, glycerol dialkyl diethers (GDDs), and archaeol (AR) with polar headgroups of monohexose (1G), dihexose (2G), trihexose (3G), and hexose-phosphohexose (HPH). Compositional and spatial distribution patterns of archaeal lipids suggest benthic Thaumarchaeota as a major source for IPLs, consistent with the predominance of Thaumarchaeota genes (>80%). The redundancy analysis (RDA) based on lipid and 16S rRNA data separates samples into three groups: extremely deep water (MT), significant terrestrial influence (NBT 1, 4, and 6), and predominant marine influence (MS, NBT 2, 3, 7, and 10). 1G-GDDs and 1G-AR positively correlate with water depth, likely reflecting the adaptation of benthic archaea to elevated hydrostatic pressure or variation of archaeal community in trench sediments. Bathyarchaeota are more abundant in sediments receiving terrestrial input; this pattern was attributed to their capability of utilizing terrestrial organic matter as an energy source. Our study highlights important environmental influences (e.g., pressure and organic matter quality and quantity) on benthic archaeal community and archaeal IPL compositions, which should be considered when IPLs and core lipids are applied as chemotaxonomic markers and paleo-proxies.

Resolving Ambient Organic Aerosol Formation and Aging Pathways with Simultaneous Molecular Composition and Volatility Observations

Lee, B; D'Ambro, EL; Lopez-Hilfiker, FD; Schobesberger, S; Mohr, C; Zawadowicz, MA; Liu, JM; Shilling, JE; Hu, WW; Palm, BB; Jimenez, JL; Hao, LQ; Virtanen, A; Zhang, HF; Goldstein, AH; Pye, HOT; Thornton, JA
2020 | ACS EARTH AND SPACE CHEMISTRY | 4 (3) (391-402)
alpha-pinene , ambient measurements , atmospheric simulation chamber , gas , hydrolysis , kinetics , mass-spectrometer , oh , ozonolysis , phase , soa formation , source and chemistry attribution , southeast united-states
Organic aerosol (OA) constitutes a significant fraction of atmospheric fine particle mass. However, the precursors and chemical processes responsible for a majority of OA are rarely conclusively identified. We use online observations of hundreds of simultaneously measured molecular components obtained from 15 laboratory OA formation experiments with constraints on their effective saturation vapor concentrations to attribute the volatile organic compound (VOC) precursors and subsequent chemical pathways giving rise to the vast majority of OA mass measured in two forested regions. We find that precursors and chemical pathways regulating OA composition and volatility are dynamic over hours to days, with their variations driven by coupled interactions between multiple oxidants. The extent of physical and photochemical aging, and its modulation by NOx, was key to a uniquely comprehensive combined composition-volatility description of OA. Our findings thus provide some of the most complete mechanistic-level guidance to the development of OA descriptions in air quality and earth system models.

On the fate of oxygenated organic molecules in atmospheric aerosol particles

Pospisilova, V; Lopez-Hilfiker, FD; Bell, DM; El Haddad, I; Mohr, C; Huang, W; Heikkinen, L; Xiao, M; Dommen, J; Prevot, ASH; Baltensperger, U; Slowik, JG
2020 | Sci. Adv. | 6 (11)
alpha-pinene , autoxidation , chemistry , mass spectrometry , oxidation , ozonolysis , part 1 , particulate matter , peroxides , spectrometer eesi-tof
Highly oxygenated organic molecules (HOMs) are formed from the oxidation of biogenic and anthropogenic gases and affect Earth's climate and air quality by their key role in particle formation and growth. While the formation of these molecules in the gas phase has been extensively studied, the complexity of organic aerosol (OA) and lack of suitable measurement techniques have hindered the investigation of their fate post-condensation, although further reactions have been proposed. We report here novel real-time measurements of these species in the particle phase, achieved using our recently developed extractive electrospray ionization time-of-flight mass spectrometer (EESI-TOF). Our results reveal that condensed-phase reactions rapidly alter OA composition and the contribution of HOMs to the particle mass. In consequence, the atmospheric fate of HOMs cannot be described solely in terms of volatility, but particle-phase reactions must be considered to describe HOM effects on the overall particle life cycle and global carbon budget.

Evaluating Organic Aerosol Sources and Evolution with a Combined Molecular Composition and Volatility Framework Using the Filter Inlet for Gases and Aerosols (FIGAERO)

Thornton, JA; Mohr, C; Schobesberger, S; D'Ambro, EL; Lee, B; Lopez-Hilfiker, FD
2020 | Acc. Chem. Res. | 53 (8) (1415-1426)
The complex array of sources and transformations of organic carbonaceous material that comprises an important fraction of atmospheric fine particle mass, known as organic aerosol, has presented a long running challenge for accurate predictions of its abundance, distribution, and sensitivity to anthropogenic activities. Uncertainties about changes in atmospheric aerosol particle sources and abundance over time translate to uncertainties in their impact on Earth's climate and their response to changes in air quality policy. One limitation in our understanding of organic aerosol has been a lack of comprehensive measurements of its molecular composition and volatility, which can elucidate sources and processes affecting its abundance. Herein we describe advances in the development and application of the Filter Inlet for Gases and Aerosols (FIGAERO) coupled to field-deployable High-Resolution Time-of-Flight Chemical Ionization Mass Spectrometers (HRToF-CIMS). The FIGAERO HRToFCIMS combination broadly probes gas and particulate OA molecular composition by using programmed thermal desorption of particles collected on a Teflon filter with subsequent detection and speciation of desorbed vapors using inherently quantitative selected-ion chemical ionization. The thermal desorption provides a means to obtain quantitative insights into the volatility of particle components and thus the physicochemical nature of the organic material that will govern its evolution in the atmosphere. In this Account, we discuss the design and operation of the FIGAERO, when coupled to the HRToF-CIMS, for quantitative characterization of the molecular-level composition and effective volatility of organic aerosol in the laboratory and field. We provide example insights gleaned from its deployment, which improve our understanding of organic aerosol sources and evolution. Specifically, we connect thermal desorption profiles to the effective equilibrium saturation vapor concentration and enthalpy of vaporization of detected components. We also show how application of the FIGAERO HRToF-CIMS to environmental simulation chamber experiments and the field provide new insights and constraints on the chemical mechanisms governing secondary organic aerosol formation and dynamic evolution. We discuss the associated challenges of thermal decomposition during desorption and calibration of both the volatility axis and signal. We also illustrate how the FIGAERO HRToF-CIMS can provide additional insights into organic aerosol through isothermal evaporation experiments as well as for detection of ultrafine particulate composition. We conclude with a description of future opportunities and needs for its ability to further organic aerosol science.

Megacity and local contributions to regional air pollution: an aircraft case study over London

Ashworth, K; Bucci, S; Gallimore, PJ; Lee, J; Nelson, BS; Sanchez-Marroquin, A; Schimpf, MB; Smith, PD; Drysdale, WS; Hopkins, JR; Lee, JD; Pitt, JR; Di Carlo, P; Krejci, R; McQuaid, JB
2020 | Atmos. Chem. Phys. | 20 (12) (7193-7216)
aerosol chemical-composition , airborne measurements , boundary layer , carbon-dioxide , co , emissions , europe , fluxes , greater london , spectrometer
In July 2017 three research flights circumnavigating the megacity of London were conducted as a part of the STANCO training school for students and early career researchers organised by EUFAR (European Facility for Airborne Research). Measurements were made from the UK's Facility for Airborne Atmospheric Measurements (FAAM) BAe-146-301 atmospheric research aircraft with the aim to sample, characterise and quantify the impact of megacity outflow pollution on air quality in the surrounding region. Conditions were extremely favourable for airborne measurements, and all three flights were able to observe clear pollution events along the flight path. A small change in wind direction provided sufficiently different air mass origins over the 2 d such that a distinct pollution plume from London, attributable marine emissions and a double-peaked dispersed area of pollution resulting from a combination of local and transported emissions were measured. We were able to analyse the effect of London emissions on air quality in the wider region and the extent to which local sources contribute to pollution events. The background air upwind of London was relatively clean during both days; concentrations of CO were 88-95 ppbv, total (measured) volatile organic compounds (VOCs) were 1.6-1.8 ppbv and NOx was 0.7-0.8 ppbv. Downwind of London, we encountered elevations in all species with CO>100 ppbv, VOCs 2.8-3.8 ppbv, CH4> 2080 ppbv and NOx >4 ppbv, and peak concentrations in individual pollution events were higher still. Levels of O-3 were inversely correlated with NOx, during the first flight, with O-3 concentrations of 37 ppbv upwind falling to similar to 26 ppbv in the well-defined London plume. Total pollutant fluxes from London were estimated through a vertical plane downwind of the city. Our calculated CO2 fluxes are within the combined uncertainty of those estimated previously, but there was a greater disparity in our estimates of CH4 and CO. On the second day, winds were lighter and downwind O-3 concentrations were elevated to similar to 39-43 ppbv (from similar to 32 to 35 ppbv upwind), reflecting the contribution of more aged pollution to the regional background. Elevations in pollutant concentrations were dispersed over a wider area than the first day, although we also encountered a number of clear transient enhancements from local sources. This series of flights demonstrated that even in a region of megacity outflow, such as the south-east of the UK, local fresh emissions and more distant UK sources of pollution can all contribute substantially to pollution events. In the highly complex atmosphere around a megacity where a high background level of pollution mixes with a variety of local sources at a range of spatial and temporal scales and atmospheric dynamics are further complicated by the urban heat island, the use of pollutant ratios to track and determine the ageing of air masses may not be valid. The individual sources must therefore all be well-characterised and constrained to understand air quality around megacities such as London. Research aircraft offer that capability through targeted sampling of specific sources and longitudinal studies monitoring trends in emission strength and profiles over time.

MIMiX: a Multipurpose In situ Microreactor system for X-ray microspectroscopy to mimic atmospheric aerosol processing

Forster, JD; Gurk, C; Lamneck, M; Tong, HJ; Ditas, F; Steimer, SS; Alpert, PA; Ammann, M; Raabe, J; Weigand, M; Watts, B; Poschl, U; Andreae, MO; Pohlker, C
2020 | Atmos. Meas. Tech. | 13 (7) (3717-3729)
beamline , cluster-analysis , humidified tdma , hygroscopic growth measurements , ice nucleation , particle critical supersaturation , phase state , physical state , spectromicroscopy , water activities

The dynamic processing of aerosols in the atmosphere is difficult to mimic under laboratory conditions, particularly on a single-particle level with high spatial and chemical resolution. Our new microreactor system for X-ray microscopy facilitates observations under in situ conditions and extends the accessible parameter ranges of existing setups to very high humidities and low temperatures. With the parameter margins for pressure (180-1000 hPa), temperature (similar to 250 K to room temperature), and relative humidity (similar to 0% to above 98 %), a wide range of tropospheric conditions is covered. Unique features are the mobile design and compact size that make the instrument applicable to different synchrotron facilities. Successful first experiments were conducted at two X-ray microscopes, MAXYMUS, located at beamline UE46 of the synchrotron BESSY II, and PolLux, located at beamline X07DA of the Swiss Light Source in the Paul Scherrer Institute. Here we present the design and analytical scope of the system, along with first results from hydration-dehydration experiments on ammonium sulfate and potassium sulfate particles and the tentative observation of water ice at low temperature and high relative humidity in a secondary organic aerosol particle from isoprene oxidation.

Temporal trends of suspect- and target-per/polyfluoroalkyl substances (PFAS), extractable organic fluorine (EOF) and total fluorine (TF) in pooled serum from first-time mothers in Uppsala, Sweden, 1996-2017

Miaz, LT; Plassmann, MM; Gyllenhammar, I; Bignert, A; Sandblom, O; Lignell, S; Glynn, A; Benskin, JP
2020 | Environ. Sci.: Processes Impacts | 22 (4) (1071-1083)

A combined method for quantitative analysis, along with suspect and non-target screening of per- and polyfluoroalkyl substances (PFAS) was developed using ultra-high pressure liquid chromatography-ultra-high resolution (Orbitrap) mass spectrometry. The method was applied together with measurements of total- and extractable organofluorine (TF and EOF, respectively), to pooled serum samples from 1996-2017 from first-time mothers living in the county of Uppsala, Sweden, some of which (i.e.148 of 472 women sampled 1996-2012) were exposed to drinking water contaminated with perfluorohexane sulfonate (PFHxS) and other PFAS until mid-2012. Declining trends were observed for all target PFAS as well as TF, with homologue-dependent differences in year of onset of decline. Only 33% of samples displayed detectable EOF, and amongst these samples the percentage of EOF explained by target PFAS declined significantly (-3.5% per year) over the entire study period. This finding corroborates prior observations in Germany after the year 2000, and may reflect increasing exposure to novel PFAS which have not yet been identified. Suspect screening revealed the presence of perfluoro-4-ethylcyclohexanesulfonate (PFECHS), which displayed declining trends since the year 2000. Non-target time trend screening revealed 3 unidentified features with time trends matching PFHxS. These features require further investigation, but may represent contaminants which co-occurred with PFHxS in the contaminated drinking water.

Role of the Air-water Interface in Removing Perfluoroalkyl Acids from Drinking Water by Activated Carbon Treatment

Meng, P.; Jiang, X.; Wang, B.; Huang, J.; Wang, Y.; Gang, Y.; Cousins, I.T.; Shubo, D.
2020 | J. Hazard. Mater. | 386 (121981)

Individual Particle Characteristics, Optical Properties and Evolution of an Extreme Long-Range Transported Biomass Burning Event in the European Arctic (Ny-angstrom lesund, Svalbard Islands)

Moroni, B; Ritter, C; Crocchianti, S; Markowicz, K; Mazzola, M; Becagli, S; Traversi, R; Krejci, R; Tunved, P; Cappelletti, D
2020 | J. Geophys. Res.-Atmos. | 125 (5)
absorption properties , aerosol evolution , aerosol optical-properties , aerosol-particles , atmospheric tar balls , black carbon , brown carbon , cavity ring , closure studies , emissions , organic acids , particle size distribution , refractive-index , sem-eds , southern africa
This paper reports an exceptional biomass burning (BB) advection event from Alaska registered at Ny-angstrom lesund from 10 to 17 July 2015 with particular interest on the influence of the airborne particle characteristics on the optical properties of the aerosol during the event. To this purpose we considered two DEKATI 12-stage aerosol samples spanning the entire advection and analyzed them by scanning electron microscopy techniques. Aerosol chemical data and microphysical properties were also evaluated in order to correlate any change of individual particle characteristics with the bulk properties of the aerosol. The results of individual particle analysis depict a complex event characterized by a first phase (P1) of massive input of BB carbonaceous particles (i.e., tar balls, popcorn refractory particles, and organic particles), and by a second phase (P2) dominated by inorganic salts. The peculiar feature of this BB event is the exceptionally large grain size of the subspherical organic particles at the beginning of the event with respect to the background. At these conditions a significant increase of the scattering efficiency may occur even for a small increase of the size parameter. Results of the simulation of the complex refractive indices (n-ik) confirm this evaluation. Aerosol evolution during the event resulted from the combination of three distinct occurrences: (a) progressive rotation of air mass circulation toward non-BB source areas, (b) development of a thick fog layer in the planetary boundary layer, and (c) sea salt spray direct advection of local/regional provenance.

Deconvolution of FIGAERO-CIMS thermal desorption profiles using positive matrix factorisation to identify chemical and physical processes during particle evaporation

Buchholz, A; Ylisirnio, A; Huang, W; Mohr, C; Canagaratna, M; Worsnop, D; Schobesberger, S; Virtanen, A
2020 | Atmos. Chem. Phys. | 20 (13) (7693-7716)
absorption-model , alpha-pinene ozonolysis , components , gas , insights , mass-spectrometer , oxidation , secondary organic aerosol , semivolatile , volatility
The measurements of aerosol particles with a filter inlet for gases and aerosols (FIGAERO) together with a chemical ionisation mass spectrometer (CIMS) yield the overall chemical composition of the particle phase. In addition, the thermal desorption profiles obtained for each detected ion composition contain information about the volatility of the detected compounds, which is an important property for understanding many physical properties like gas-particle partitioning. We coupled this thermal desorption method with isothermal evaporation prior to the sample collection to investigate the chemical composition changes during isothermal particle evaporation and particulate-water-driven chemical reactions in alpha-pinene secondary organic aerosol (SOA) of three different oxidative states. The thermal desorption profiles of all detected elemental compositions were then analysed with positive matrix factorisation (PMF) to identify the drivers of the chemical composition changes observed during isothermal evaporation. The keys to this analysis were to use the error matrix as a tool to weight the parts of the data carrying most information (i.e. the peak area of each thermogram) and to run PMF on a combined data set of multiple thermograms from different experiments to enable a direct comparison of the individual factors between separate measurements. The PMF was able to identify instrument background factors and separate them from the part of the data containing particle desorption information. Additionally, PMF allowed us to separate the direct desorption of compounds detected at a specific elemental composition from other signals with the same composition that stem from the thermal decomposition of thermally instable compounds with lower volatility. For each SOA type, 7-9 factors were needed to explain the observed thermogram behaviour. The contribution of the factors depended on the prior isothermal evaporation. Decreased contributions from the factors with the lowest desorption temperatures were observed with increasing isothermal evaporation time. Thus, the factors identified by PMF could be interpreted as volatility classes. The composition changes in the particles due to isothermal evaporation could be attributed to the removal of volatile factors with very little change in the desorption profiles of the individual factors (i.e. in the respective temperatures of peak desorption, T-max). When aqueous-phase reactions took place, PMF was able to identify a new factor that directly identified the ions affected by the chemical processes. We conducted a PMF analysis of the FIGAERO-CIMS thermal desorption data for the first time using laboratory-generated SOA particles. But this method can be applied to, for example, ambient FIGAERO-CIMS measurements as well. There, the PMF analysis of the thermal desorption data identifies organic aerosol (OA) sources (such as biomass burning or oxidation of different precursors) and types, e.g. hydrocarbon-like (HOA) or oxygenated organic aerosol (OOA). This information could also be obtained with the traditional approach, namely the PMF analysis of the mass spectra data integrated for each thermogram. But only our method can also obtain the volatility information for each OA source and type. Additionally, we can identify the contribution of thermal decomposition to the overall signal.

Size-segregated particle number and mass concentrations from different emission sources in urban Beijing

Cai, J; Chu, BW; Yao, L; Yan, C; Heikkinen, LM; Zheng, FX; Li, C; Fan, XL; Zhang, SJ; Yang, DY; Wang, YH; Kokkonen, TV; Chan, T; Zhou, Y; Dada, L; Liu, YC; He, H; Paasonen, P; Kujansuu, JT; Petaja, T; Mohr, C; Kangasluoma, J; Bianchi, F; Sun, YL; Croteau, PL; Worsnop, DR; Kerminen, VM; Du, W; Kulmala, M; Daellenbach, KR
2020 | Atmos. Chem. Phys. | 20 (21) (12721-12740)
air-pollution sources , black carbon , chemical speciation monitor , particulate matter , resolved effective density , seasonal-variations , secondary organic aerosol , source apportionment , source identification , submicron aerosols
Although secondary particulate matter is reported to be the main contributor of PM2.5 during haze in Chinese megacities, primary particle emissions also affect particle concentrations. In order to improve estimates of the contribution of primary sources to the particle number and mass concentrations, we performed source apportionment analyses using both chemical fingerprints and particle size distributions measured at the same site in urban Beijing from April to July 2018. Both methods resolved factors related to primary emissions, including vehicular emissions and cooking emissions, which together make up 76% and 24% of total particle number and organic aerosol (OA) mass, respectively. Similar source types, including particles related to vehicular emissions (1.6 +/- 1.1 mu gm(-3); 2.4 +/- 1.8 x 10(3) cm(-3) and 5.5 +/- 2.8 x 10(3) cm(-3) for two traffic-related components), cooking emissions (2.6 +/- 1.9 mu gm(-3) and 5.5 +/- 3.3 x 10(3) cm(-3)) and secondary aerosols (51 +/- 41 mu gm(-3) and 4.2 +/- 3.0 x 10(3) cm(-3)), were resolved by both methods. Converted mass concentrations from particle size distributions components were comparable with those from chemical fingerprints. Size distribution source apportionment separated vehicular emissions into a component with a mode diameter of 20 nm ("traffic-ultrafine") and a component with a mode diameter of 100 nm ("traffic-fine"). Consistent with similar day- and nighttime diesel vehicle PM2.5 emissions estimated for the Beijing area, traffic-fine particles, hydrocarbon-like OA (HOA, traffic-related factor resulting from source apportionment using chemical fingerprints) and black carbon (BC) showed similar diurnal patterns, with higher concentrations during the night and morning than during the afternoon when the boundary layer is higher. Traffic-ultrafine particles showed the highest concentrations during the rush-hour period, suggesting a prominent role of local gasoline vehicle emissions. In the absence of new particle formation, our re-sults show that vehicular-related emissions (14% and 30% for ultrafine and fine particles, respectively) and cooking-activity-related emissions (32 %) dominate the particle number concentration, while secondary particulate matter (over 80 %) governs PM2.5 mass during the non-heating season in Beijing.

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