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- ItemLong-term measurements of aerosol and carbon monoxide at the ZOTTO tall tower to characterize polluted and pristine air in the Siberian taiga(München : European Geopyhsical Union, 2013) Chi, X.; Winderlich, J.; Mayer, J.-C.; Panov, A.V.; Heimann, M.; Birmili, W.; Heintzenberg, J.; Cheng, Y.; Andreae, M.O.Siberia is one of few continental regions in the Northern Hemisphere where the atmosphere may sometimes approach pristine background conditions. We present the time series of aerosol and carbon monoxide (CO) measurements between September 2006 and December 2011 at the Zotino Tall Tower Observatory (ZOTTO) in Central Siberia (61° N; 89° E). We investigate the seasonal, weekly and diurnal variations of aerosol properties (including absorption and scattering coefficients and derived parameters, such as equivalent black carbon (BCe), Ångström exponent, single scattering albedo, and backscattering ratio) and the CO mixing ratios. Criteria were established to distinguish polluted from near-pristine air masses, providing quantitative characteristics for each type. Depending on the season, 23–36% of the sampling time at ZOTTO was found to be representative of a clean atmosphere. The summer pristine data indicate that primary biogenic and secondary organic aerosol formation are quite strong particle sources in the Siberian taiga. The summer seasons 2007–2008 were dominated by an Aitken mode around 80 nm size, whereas the summer 2009 with prevailing easterly winds produced particles in the accumulation mode around 200 nm size. We found these differences to be mainly related to air temperature, through its effect on the production rates of biogenic volatile organic compounds (VOC) precursor gases. In winter, the particle size distribution peaked at 160 nm, and the footprint of clean background air was characteristic for aged particles from anthropogenic sources at great distances from ZOTTO and diluted biofuel burning emissions from domestic heating. The wintertime polluted air originates mainly from large cities south and southwest of the site; these particles have a dominant mode around 100 nm, and the ΔBCe / ΔCO ratio of 7–11 ng m−3 ppb−1 suggests dominant contributions from coal and biofuel burning for heating. During summer, anthropogenic emissions are the dominant contributor to the pollution particles at ZOTTO, while only 12% of the polluted events are classified as biomass-burning-dominated, but then often associated with extremely high CO concentrations and aerosol absorption coefficients. Two biomass-burning case studies revealed different ΔBCe / ΔCO ratios from different fire types, with the agricultural fires in April~2008 yielding a very high ratio of 21 ng m−3 ppb−1. Overall, we find that anthropogenic sources dominate the aerosol population at ZOTTO most of the time, even during nominally clean episodes in winter, and that near-pristine conditions are encountered only in the growing season and then only episodically.
- ItemHygroscopic properties of atmospheric aerosol particles over the Eastern Mediterranean: Implications for regional direct radiative forcing under clean and polluted conditions(München : European Geopyhsical Union, 2011) Stock, M.; Cheng, Y.F.; Birmili, W.; Massling, A.; Wehner, B.; Müller, T.; Leinert, S.; Kalivitis, N.; Mihalopoulos, N.; Wiedensohler, A.This work examines the effect of direct radiative forcing of aerosols in the eastern Mediterranean troposphere as a function of air mass composition, particle size distribution and hygroscopicity, and relative humidity (RH). During intensive field measurements on the island of Crete, Greece, the hygroscopic properties of atmospheric particles were determined using a Hygroscopicity Tandem Differential Mobility Analyzer (H-TDMA) and a Hygroscopicity Differential Mobility Analyzer-Aerodynamic Particle Sizer (H-DMA-APS). Similar to former studies, the H-TDMA identified three hygroscopic sub-fractions of particles in the sub-μm range: a more hygroscopic group, a less hygroscopic group and a nearly hydrophobic particle group. The average hygroscopic particle growth factors at 90 % RH were a significant function of particle mobility diameter (Dp): 1.42 (± 0.05) at 30 nm compared to 1.63 (± 0.07) at 250 nm. The H-DMA-APS identified up to three hygroscopic sub-fractions at mobility diameters of 1.0 and 1.2 μm. The data recorded between 12 August and 20 October 2005 were classified into four distinct synoptic-scale air mass types distinguishing between different regions of origin (western Mediterranean vs. the Aegean Sea) as well as the degree of continental pollution (marine vs. continentally influenced). The hygroscopic properties of particles with diameter Dp≥150 nm showed the most pronounced dependency on air mass origin, with growth factors in marine air masses exceeding those in continentally influenced air masses. Particle size distributions and hygroscopic growth factors were used to calculate aerosol light scattering coefficients at ambient RH using a Mie model. A main result was the pronounced enhancement of particle scattering over the eastern Mediterranean due to hygroscopic growth, both in the marine and continentally influenced air masses. When RH reached its summer daytime values around 70–80 %, up to 50–70 % of the calculated visibility reduction was due to the hygroscopic growth of the particles by water compared to the effect of the dry particles alone. The estimated aerosol direct radiative forcings for both, marine and continentally influenced air masses were negative indicating a net cooling of the atmosphere due to the aerosol. The radiative forcing ΔFr was nevertheless governed by the total aerosol concentration most of the time: ΔFr was typically more negative for continentally influenced aerosols (ca. −4 W m−2) compared to rather clean marine aerosols (ca. −1.5 W m−2). When RH occasionally reached 90 % in marine air masses, ΔFr even reached values down to −7 W m−2. Our results emphasize, on the basis of explicit particle hygroscopicity measurements, the relevance of ambient RH for the radiative forcing of regional atmospheres.
- ItemInflux of African biomass burning aerosol during the Amazonian dry season through layered transatlantic transport of black carbon-rich smoke(Katlenburg-Lindau : EGU, 2020) Holanda, Bruna A.; Pöhlker, Mira L.; Walter, David; Saturno, Jorge; Sörgel, Matthias; Ditas, Jeannine; Ditas, Florian; Schulz, Christiane; Aurélio Franco, Marco; Wang, Qiaoqiao; Donth, Tobias; Artaxo, Paulo; Barbosa, Henrique M.J.; Borrmann, Stephan; Braga, Ramon; Brito, Joel; Cheng, Yafang; Dollner, Maximilian; Kaiser, JohannesW.; Klimach, Thomas; Knote, Christoph; Krüger, Ovid O.; Fütterer, Daniel; Lavrič, Jošt V.; Ma, Nan; Machado, Luiz A.T.; Ming, Jing; Morais, Fernando G.; Paulsen, Hauke; Sauer, Daniel; Schlager, Hans; Schneider, Johannes; Su, Hang; Weinzierl, Bernadett; Walser, Adrian; Wendisch, Manfred; Ziereis, Helmut; Zöger, Martin; Pöschl, Ulrich; Andreae, Meinrat O.; Pöhlker, ChristopherBlack carbon (BC) aerosols influence the Earth's atmosphere and climate, but their microphysical properties, spatiotemporal distribution, and long-range transport are not well constrained. This study presents airborne observations of the transatlantic transport of BC-rich African biomass burning (BB) smoke into the Amazon Basin using a Single Particle Soot Photometer (SP2) as well as several complementary techniques. We base our results on observations of aerosols and trace gases off the Brazilian coast onboard the HALO (High Altitude and LOng range) research aircraft during the ACRIDICON-CHUVA campaign in September 2014. During flight AC19 over land and ocean at the northeastern coastline of the Amazon Basin, we observed a BCrich layer at ∼ 3:5 km altitude with a vertical extension of ∼ 0:3 km. Backward trajectories suggest that fires in African grasslands, savannas, and shrublands were the main source of this pollution layer and that the observed BB smoke had undergone more than 10 d of atmospheric transport and aging over the South Atlantic before reaching the Amazon Basin. The aged smoke is characterized by a dominant accumulation mode, centered at about 130 nm, with a particle concentration of Nacc D 850±330 cm-3. The rBC particles account for ∼ 15 % of the submicrometer aerosol mass and ∼ 40 % of the total aerosol number concentration. This corresponds to a mass concentration range from 0.5 to 2 μ g m-3 (1st to 99th percentiles) and a number concentration range from 90 to 530 cm-3. Along with rBC, high cCO (150 ± 30 ppb) and cO3 (56 ± 9 ppb) mixing ratios support the biomass burning origin and pronounced photochemical aging of this layer. Upon reaching the Amazon Basin, it started to broaden and to subside, due to convective mixing and entrainment of the BB aerosol into the boundary layer. Satellite observations show that the transatlantic transport of pollution layers is a frequently occurring process, seasonally peaking in August/September. By analyzing the aircraft observations together with the long-term data from the Amazon Tall Tower Observatory (ATTO), we found that the transatlantic transport of African BB smoke layers has a strong impact on the northern and central Amazonian aerosol population during the BBinfluenced season (July to December). In fact, the early BB season (July to September) in this part of the Amazon appears to be dominated by African smoke, whereas the later BB season (October to December) appears to be dominated by South American fires. This dichotomy is reflected in pronounced changes in aerosol optical properties such as the single scattering albedo (increasing from 0.85 in August to 0.90 in November) and the BC-to-CO enhancement ratio (decreasing from 11 to 6 ng m-3 ppb-1). Our results suggest that, despite the high fraction of BC particles, the African BB aerosol acts as efficient cloud condensation nuclei (CCN), with potentially important implications for aerosol-cloud interactions and the hydrological cycle in the Amazon. © 2020 Author(s).
- 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.
- ItemCloud condensation nuclei spectra derived from size distributions and hygroscopic properties of the aerosol in coastal south-west Portugal during ACE-2(Milton Park : Taylor & Francis, 2016) Dusek, Ulrike; Covert, David S.; Wiedensohler, Alfred; Neusüss, Christian; Weise, Diana; Cantrell, WillIn this work we propose and test a method to calculate cloud condensation nuclei (CCN) spectra basedon aerosol number size distributions and hygroscopic growth factors. Sensitivity studies show thatthis method can be used in a wide variety of conditions except when the aerosol consist mainly oforganic compounds. One crucial step in the calculations, estimating soluble ions in an aerosol particlebased on hygroscopic growth factors, is tested in an internal hygroscopic consistency study. The resultsshow that during the second Aerosol Characterization Experiment (ACE-2) the number concentrationof inorganic ions analyzed in impactor samples could be reproduced from measured growth factorswithin the measurement uncertainties at the measurement site in Sagres, Portugal. CCN spectra were calculated based on data from the ACE-2 field experiment at the Sagres site.The calculations overestimate measured CCN spectra on average by approximately 30%, which iscomparable to the uncertainties in measurements and calculations at supersaturations below 0.5%. Thecalculated CCN spectra were averaged over time periods when Sagres received clean air masses and airmasses influenced by aged and recent pollution. Pollution outbreaks enhance the CCN concentrationsat supersaturations near 0.2% by a factor of 3 (aged pollution) to 5 (recent pollution) compared to theclean marine background concentrations. In polluted air masses, the shape of the CCN spectra changes.The clean spectra can be approximated by a power function, whereas the polluted spectra are betterapproximated by an error function.