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- ItemMultiphase MCM-CAPRAM modeling of the formation and processing of secondary aerosol constituents observed during the Mt. Tai summer campaign in 2014(Katlenburg-Lindau : EGU, 2020) Zhu, Yanhong; Tilgner, Andreas; Hoffmann, Erik Hans; Herrmann, Hartmut; Kawamura, Kimitaka; Yang, Lingxiao; Xue, Likun; Wang, WenxingDespite the high abundance of secondary aerosols in the atmosphere, their formation mechanisms remain poorly understood. In this study, the Master Chemical Mechanism (MCM) and the Chemical Aqueous-Phase Radical Mechanism (CAPRAM) are used to investigate the multiphase formation and processing of secondary aerosol constituents during the advection of air masses towards the measurement site of Mt. Tai in northern China. Trajectories with and without chemical–cloud interaction are modeled. Modeled radical and non-radical concentrations demonstrate that the summit of Mt. Tai, with an altitude of ∼1.5 km a.m.s.l., is characterized by a suburban oxidants budget. The modeled maximum gas-phase concentrations of the OH radical are 3.2×106 and 3.5×106 molec. cm−3 in simulations with and without cloud passages in the air parcel, respectively. In contrast with previous studies at Mt. Tai, this study has modeled chemical formation processes of secondary aerosol constituents under day vs. night and cloud vs. non-cloud cases along the trajectories towards Mt. Tai in detail. The model studies show that sulfate is mainly produced in simulations where the air parcel is influenced by cloud chemistry. Under the simulated conditions, the aqueous reaction of HSO−3 with H2O2 is the major contributor to sulfate formation, contributing 67 % and 60 % in the simulations with cloud and non-cloud passages, respectively. The modeled nitrate formation is higher at nighttime than during daytime. The major pathway is aqueous-phase N2O5 hydrolysis, with a contribution of 72 % when cloud passages are considered and 70 % when they are not. Secondary organic aerosol (SOA) compounds, e.g., glyoxylic, oxalic, pyruvic and malonic acid, are found to be mostly produced from the aqueous oxidations of hydrated glyoxal, hydrated glyoxylic acid, nitro-2-oxopropanoate and hydrated 3-oxopropanoic acid, respectively. Sensitivity studies reveal that gaseous volatile organic compound (VOC) emissions have a huge impact on the concentrations of modeled secondary aerosol compounds. Increasing the VOC emissions by a factor of 2 leads to linearly increased concentrations of the corresponding SOA compounds. Studies using the relative incremental reactivity (RIR) method have identified isoprene, 1,3-butadiene and toluene as the key precursors for glyoxylic and oxalic acid, but only isoprene is found to be a key precursor for pyruvic acid. Additionally, the model investigations demonstrate that an increased aerosol partitioning of glyoxal can play an important role in the aqueous-phase formation of glyoxylic and oxalic acid. Overall, the present study is the first that provides more detailed insights in the formation pathways of secondary aerosol constituents at Mt. Tai and clearly emphasizes the importance of aqueous-phase chemical processes on the production of multifunctional carboxylic acids.
- ItemIn situ, satellite measurement and model evidence on the dominant regional contribution to fine particulate matter levels in the Paris megacity(Katlenburg-Lindau : EGU, 2015) Beekmann, M.; Prévôt, A.S.H.; Drewnick, F.; Sciare, J.; Pandis, S.N.; Denier van der Gon, H.A.C.; Crippa, M.; Freutel, F.; Poulain, L.; Ghersi, V.; Rodriguez, E.; Beirle, S.; Zotter, P.; von der Weiden-Reinmüller, S.-L.; Bressi, M.; Fountoukis, C.; Petetin, H.; Szidat, S.; Schneider, J.; Rosso, A.; El Haddad, I.; Megaritis, A.; Zhang, Q.J.; Michoud, V.; Slowik, J.G.; Moukhtar, S.; Kolmonen, P.; Stohl, A.; Eckhardt, S.; Borbon, A.; Gros, V.; Marchand, N.; Jaffrezo, J.L.; Schwarzenboeck, A.; Colomb, A.; Wiedensohler, A.; Borrmann, S.; Lawrence, M.; Baklanov, A.; Baltensperger, U.A detailed characterization of air quality in the megacity of Paris (France) during two 1-month intensive campaigns and from additional 1-year observations revealed that about 70 % of the urban background fine particulate matter (PM) is transported on average into the megacity from upwind regions. This dominant influence of regional sources was confirmed by in situ measurements during short intensive and longer-term campaigns, aerosol optical depth (AOD) measurements from ENVISAT, and modeling results from PMCAMx and CHIMERE chemistry transport models. While advection of sulfate is well documented for other megacities, there was surprisingly high contribution from long-range transport for both nitrate and organic aerosol. The origin of organic PM was investigated by comprehensive analysis of aerosol mass spectrometer (AMS), radiocarbon and tracer measurements during two intensive campaigns. Primary fossil fuel combustion emissions constituted less than 20 % in winter and 40 % in summer of carbonaceous fine PM, unexpectedly small for a megacity. Cooking activities and, during winter, residential wood burning are the major primary organic PM sources. This analysis suggests that the major part of secondary organic aerosol is of modern origin, i.e., from biogenic precursors and from wood burning. Black carbon concentrations are on the lower end of values encountered in megacities worldwide, but still represent an issue for air quality. These comparatively low air pollution levels are due to a combination of low emissions per inhabitant, flat terrain, and a meteorology that is in general not conducive to local pollution build-up. This revised picture of a megacity only being partially responsible for its own average and peak PM levels has important implications for air pollution regulation policies.
- ItemMutual promotion between aerosol particle liquid water and particulate nitrate enhancement leads to severe nitrate-dominated particulate matter pollution and low visibility(Katlenburg-Lindau : EGU, 2020) Wang, Yu; Chen, Ying; Wu, Zhijun; Shang, Dongjie; Bian, Yuxuan; Du, Zhuofei; Schmitt, Sebastian H.; Su, Rong; Gkatzelis, Georgios I.; Schlag, Patrick; Hohaus, Thorsten; Voliotis, Aristeidis; Lu, Keding; Zeng, Limin; Zhao, Chunsheng; Alfarra, M. Rami; McFiggans, Gordon; Wiedensohler, Alfred; Kiendler-Scharr, Astrid; Zhang, Yuanhang; Hu, MinAs has been the case in North America and western Europe, the SO2 emissions have substantially reduced in the North China Plain (NCP) in recent years. Differential rates of reduction in SO2 and NOx concentrations result in the frequent occurrence of particulate matter pollution dominated by nitrate (pNO−3) over the NCP. In this study, we observed a polluted episode with the particulate nitrate mass fraction in nonrefractory PM1 (NR-PM1) being up to 44 % during wintertime in Beijing. Based on this typical pNO−3-dominated haze event, the linkage between aerosol water uptake and pNO−3 enhancement, further impacting on visibility degradation, has been investigated based on field observations and theoretical calculations. During haze development, as ambient relative humidity (RH) increased from ∼10 % to 70 %, the aerosol particle liquid water increased from ∼1 µg m−3 at the beginning to ∼75 µg m−3 in the fully developed haze period. The aerosol liquid water further increased the aerosol surface area and volume, enhancing the condensational loss of N2O5 over particles. From the beginning to the fully developed haze, the condensational loss of N2O5 increased by a factor of 20 when only considering aerosol surface area and volume of dry particles, while increasing by a factor of 25 when considering extra surface area and volume due to water uptake. Furthermore, aerosol liquid water favored the thermodynamic equilibrium of HNO3 in the particle phase under the supersaturated HNO3 and NH3 in the atmosphere. All the above results demonstrated that pNO−3 is enhanced by aerosol water uptake with elevated ambient RH during haze development, in turn facilitating the aerosol take-up of water due to the hygroscopicity of particulate nitrate salt. Such mutual promotion between aerosol particle liquid water and particulate nitrate enhancement can rapidly degrade air quality and halve visibility within 1 d. Reduction of nitrogen-containing gaseous precursors, e.g., by control of traffic emissions, is essential in mitigating severe haze events in the NCP.
- ItemBiochar as a tool to reduce the agricultural greenhouse-gas burden–knowns, unknowns and future research needs(Vilnius : Technika, 2017) Kammann, Claudia; Ippolito, Jim; Hagemann, Nikolas; Borchard, Nils; Cayuela, Maria Luz; Estavillo, José M.; Fuertes-Mendizabal, Teresa; Jeffery, Simon; Kern, Jürgen; Novak, Jeff; Rasse, Daniel; Saarnio, Sanna; Schmidt, Hans-Peter; Spokas, Kurt; Wrage-Mönnig, NicoleAgriculture and land use change has significantly increased atmospheric emissions of the non-CO2 green-house gases (GHG) nitrous oxide (N2O) and methane (CH4). Since human nutritional and bioenergy needs continue to increase, at a shrinking global land area for production, novel land management strategies are required that reduce the GHG footprint per unit of yield. Here we review the potential of biochar to reduce N2O and CH4 emissions from agricultural practices including potential mechanisms behind observed effects. Furthermore, we investigate alternative uses of biochar in agricultural land management that may significantly reduce the GHG-emissions-per-unit-of-product footprint, such as (i) pyrolysis of manures as hygienic alternative to direct soil application, (ii) using biochar as fertilizer carrier matrix for underfoot fertilization, biochar use (iii) as composting additive or (iv) as feed additive in animal husbandry or for manure treatment. We conclude that the largest future research needs lay in conducting life-cycle GHG assessments when using biochar as an on-farm management tool for nutrient-rich biomass waste streams. © 2017 The Author(s) Published by VGTU Press and Informa UK Limited, [trading as Taylor & Francis Group].
- ItemMulti-generation OH oxidation as a source for highly oxygenated organic molecules from aromatics(Katlenburg-Lindau : EGU, 2020) Garmash, Olga; Rissanen, Matti P.; Pullinen, Iida; Schmit, Sebastian; Kausiala, Oskari; Tillmann, Ralf; Zhao, Defeng; Percival, Carl; Bannan, Thomas J.; Priestley, Michael; Hallquist, Åsa M.; Kleist, Einhard; Kiendler-Scharr, Astrid; Hallquist, Mattias; Berndt, Torsten; McFiggans, Gordon; Wildt, Jürgen; Mentel, Thomas F.; Ehn, MikaelRecent studies have recognised highly oxygenated organic molecules (HOMs) in the atmosphere as important in the formation of secondary organic aerosol (SOA). A large number of studies have focused on HOM formation from oxidation of biogenically emitted monoterpenes. However, HOM formation from anthropogenic vapours has so far received much less attention. Previous studies have identified the importance of aromatic volatile organic compounds (VOCs) for SOA formation. In this study, we investigated several aromatic compounds, benzene (C6H6), toluene (C7H8), and naphthalene (C10H8), for their potential to form HOMs upon reaction with hydroxyl radicals (OH). We performed flow tube experiments with all three VOCs and focused in detail on benzene HOM formation in the Julich Plant Atmosphere Chamber (JPAC). In JPAC, we also investigated the response of HOMs to NOx and seed aerosol. Using a nitrate-based chemical ionisation mass spectrometer (CI-APi-TOF), we observed the formation of HOMs in the flow reactor oxidation of benzene from the first OH attack. However, in the oxidation of toluene and naphthalene, which were injected at lower concentrations, multigeneration OH oxidation seemed to impact the HOM composition. We tested this in more detail for the benzene system in the JPAC, which allowed for studying longer residence times. The results showed that the apparent molar benzene HOM yield under our experimental conditions varied from 4.1% to 14.0 %, with a strong dependence on the OH concentration, indicating that the majority of observed HOMs formed through multiple OH-oxidation steps. The composition of the identified HOMs in the mass spectrum also supported this hypothesis. By injecting only phenol into the chamber, we found that phenol oxidation cannot be solely responsible for the observed HOMs in benzene experiments. When NOx was added to the chamber, HOM composition changed and many oxygenated nitrogen-containing products were observed in CI-APi-TOF. Upon seed aerosol injection, the HOM loss rate was higher than predicted by irreversible condensation, suggesting that some undetected oxygenated intermediates also condensed onto seed aerosol, which is in line with the hypothesis that some of the HOMs were formed in multi-generation OH oxidation. Based on our results, we conclude that HOM yield and composition in aromatic systems strongly depend on OH and VOC concentration and more studies are needed to fully understand this effect on the formation of HOMs and, consequently, SOA. We also suggest that the dependence of HOM yield on chamber conditions may explain part of the variability in SOA yields reported in the literature and strongly advise monitoring HOMs in future SOA studies. © Author(s) 2020.
- ItemChemical composition of cloud water in the puerto rican tropical trade wind cumuli(Dordrecht : Springer, 2009) Gioda, A.; Mayol-Bracero, O.L.; Morales-GarcÃa, F.; Collett, J.; Decesari, S.; Emblico, L.; Facchini, M.C.; Morales-De Jesús, R.J.; Mertes, S.; Borrmann, S.; Walter, S.; Schneider, J.As part of the Rain In Cumulus over the Ocean Experiment (RICO) and the Puerto Rico Aerosol and Cloud Study (PRACS), cloud water was collected at East Peak (EP) in Puerto Rico. The main objective of this study was to determine the concentrations of water-soluble species (Cl-, NO3 -, SO4 2-, NH4 +, Ca 2+, H+, Mg2+, K+, and Na +) in water samples taken from clouds influenced by tropical trade winds. The most abundant inorganic species were Na+ (average 465 μeq l-1) and Cl- (434 μeq l-1), followed by Mg2+ (105 μeq l-1), SO4 2- (61 μeq l-1), and NO3 - (25 μeq l -1). High concentrations of nss-SO4 2 (28 μeq l-1), NO3 - (86 μeq l-1), and H+ (14.5 μeq l-1) were measured with a shift in air masses origin from the North Atlantic to North American continent, which reflected a strong anthropogenic influence on cloud chemistry at EP. Long-range transport of particles and acid gases seems to be the factor responsible for fluctuations in concentrations and pH of cloud water at East Peak. When under trade wind influences the liquid phase concentrations of all inorganic substances were similar to those found in clouds in other clean maritime environments. © 2008 Springer Science+Business Media B.V.