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Karlheinz Schaber - One of the best experts on this subject based on the ideXlab platform.
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Formation of hydrobromic and hydrochloric acid Aerosols in wet flue gas cleaning processes
Chemical Engineering Communications, 2013Co-Authors: S Sinanis, A Wix, Karlheinz SchaberAbstract:The Formation and behavior of hydrobromic and hydrochloric acid Aerosols in a wet flue gas cleaning pilot plant were investigated. The optical three-wavelength extinction (3-WE) method was used to determine mean Aerosol droplet diameters and droplet number concentrations. The experimental data are compared with theoretical results of the simulation tool AerCoDe (Aerosol Formation in contact devices). Results are presented for a raw gas temperature of 200°C and raw gas concentrations up to 260 mg/m3(STP) for HBr, and 2500 mg/m3 (STP) for HCl. Under these conditions Aerosol Formation for both species is initiated by heterogeneous nucleation. It is shown that during absorption processes HBr is forming essentially higher supersaturated gas phases in comparison to HCl, resulting in higher droplet number concentrations and smaller droplet sizes. For both species the number concentration is a strong function of the maximum degree of saturation, which corresponds to the classical theory of heterogeneous nucleatio...
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a simulation tool for Aerosol Formation during sulphuric acid absorption in a gas cleaning process
Journal of Aerosol Science, 2010Co-Authors: L Brachert, S Sinanis, Karlheinz SchaberAbstract:Abstract A simulation tool has been developed to predict sulphuric acid Aerosol Formation in typical industrial absorption processes for gas cleaning. The underlying model comprises homogeneous nucleation and the growth of a polydisperse droplet collective under the special circumstances of a gas–liquid contact device where heat and mass transfer processes between the bulk phases take place simultaneously. The model is applied to a hot flue gas (200 °C) with sulphuric acid concentrations between 5 and 100 mg m −3 (STP) (STP: standard temperature and pressure ) . The simulation yields high droplet number concentrations up to 10 16 m −3 especially for low gas inlet concentrations of sulphuric acid (5 mg m −3 (STP)), and very small droplet sizes in the range 20–100 nm. The droplet number concentrations decrease and the droplet sizes increase with increasing sulphuric acid inlet concentrations. It is shown that small droplets (
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characterization of sulphuric acid and ammonium sulphate Aerosols in wet flue gas cleaning processes
Chemical Engineering and Processing, 2008Co-Authors: S Sinanis, Karlheinz SchaberAbstract:Abstract Sulphuric acid Aerosols can be formed in wet flue gas cleaning processes by spontaneous condensation initiated mainly by homogeneous nucleation. Even at low gas inlet concentrations of SO 3 (2 mg/m 3 (STP)) Aerosol Formation can be observed. For the design of absorption processes and sulphuric acid mist precipitators the Aerosol characteristic data like mean diameter and number concentration are required for different process conditions and raw gas concentrations. In the present contribution, a combination of an experimental method with the simulation tool AerCode is described, which permits the determination of the diameter and the number concentration of sulphuric acid Aerosols formed in wet flue gas cleaning processes. As a result of the extreme azeotropic phase behaviour of the H 2 SO 4 –H 2 O system the mechanism of homogeneous nucleation is predominant for Aerosol Formation in absorption processes. Furthermore, the influence of soluble and insoluble particles on homogeneous nucleation in the system H 2 SO 4 –H 2 O is shown. The investigation of the influence of insoluble foreign nuclei shows that at high SO 3 raw gas concentrations >30 mg/m 3 (STP), the mechanism of homogeneous nucleation is predominant. At lower raw gas concentrations between 2 and 10 mg/m 3 (STP) SO 3 heterogeneous nucleation is the major reason for Aerosol Formation. Solid (NH 4 ) 2 SO 4 particles that are formed by the reaction between H 2 SO 4 and NH 3 in the gas phase are used as soluble foreign nuclei. The studies show that Aerosol Formation is determined by the reaction component whose concentration is below the stoichiometric ratio. It was observed that in the case of an excess of sulphuric acid a decrease of the amount of ammonia leads to an increase of the particle size combined with a decrease in the number concentration. If ammonia is in excess, the decrease in the concentration of ammonia changes neither the particle size nor the number concentration of the Aerosol significantly.
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characterization of sulphuric acid and ammonium sulphate Aerosols in wet flue gas cleaning processes
Chemical Engineering and Processing, 2008Co-Authors: S Sinanis, Karlheinz SchaberAbstract:Abstract Sulphuric acid Aerosols can be formed in wet flue gas cleaning processes by spontaneous condensation initiated mainly by homogeneous nucleation. Even at low gas inlet concentrations of SO 3 (2 mg/m 3 (STP)) Aerosol Formation can be observed. For the design of absorption processes and sulphuric acid mist precipitators the Aerosol characteristic data like mean diameter and number concentration are required for different process conditions and raw gas concentrations. In the present contribution, a combination of an experimental method with the simulation tool AerCode is described, which permits the determination of the diameter and the number concentration of sulphuric acid Aerosols formed in wet flue gas cleaning processes. As a result of the extreme azeotropic phase behaviour of the H 2 SO 4 –H 2 O system the mechanism of homogeneous nucleation is predominant for Aerosol Formation in absorption processes. Furthermore, the influence of soluble and insoluble particles on homogeneous nucleation in the system H 2 SO 4 –H 2 O is shown. The investigation of the influence of insoluble foreign nuclei shows that at high SO 3 raw gas concentrations >30 mg/m 3 (STP), the mechanism of homogeneous nucleation is predominant. At lower raw gas concentrations between 2 and 10 mg/m 3 (STP) SO 3 heterogeneous nucleation is the major reason for Aerosol Formation. Solid (NH 4 ) 2 SO 4 particles that are formed by the reaction between H 2 SO 4 and NH 3 in the gas phase are used as soluble foreign nuclei. The studies show that Aerosol Formation is determined by the reaction component whose concentration is below the stoichiometric ratio. It was observed that in the case of an excess of sulphuric acid a decrease of the amount of ammonia leads to an increase of the particle size combined with a decrease in the number concentration. If ammonia is in excess, the decrease in the concentration of ammonia changes neither the particle size nor the number concentration of the Aerosol significantly.
Markku Kulmala - One of the best experts on this subject based on the ideXlab platform.
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Aerosol Formation over the boreal forest in hyytiala finland monthly frequency and annual cycles the roles of air mass characteristics and synoptic scale meteorology
Atmospheric Chemistry and Physics, 2006Co-Authors: E D Nilsson, Markku KulmalaAbstract:Abstract. New atmospheric particles with diameters of 3–10 nm and their subsequent growth to cloud condensation nucleus have been observed at various places in the European boundary layer. These events have been observed simultaneously within wide geographical areas (over 1000 km) in connection to specific weather systems, the cold air behind cyclones. Here we show that atmospheric Aerosol Formation (i.e. nucleation and initial growth) is favoured by the outbreak of cold Arctic air over northern Europe. Aerosol Formation was about twice as common in Arctic air as in sub-Polar air, and even more so compared to other air masses. The most important general factor favouring Aerosol Formation in Arctic air and marine air was weaker competing condensational sink (CS) for the precursor gases (less pre-existing Aerosols), while high CS prevented Aerosol Formation in heated sub-Polar air and mid-latitude air. High SO2 levels favoured nucleation in continental air and high UV-B radiation in sub-tropical air. The critical factor that determined if Aerosol Formation would start on a day with Arctic air was the UV-B radiation. The same applied to sub-Polar air and continental air, while increased SO2 concentration could trigger Formation in heated sub-Polar and mid-latitude air, and reduced CS could cause Formation in mid-latitude, marine or mixed/transient air. We speculate that strong emissions of volatile organic compounds from the Boreal forest and strong boundary layer dynamics may have caused Aerosol Formation in sub-Polar air masses and air in transition from a marine to a continental character. The monthly frequency of Arctic air masses and the probability for photo-chemically driven Aerosol Formation explains the observed annual cycle in monthly particle Formation frequency as well as much of the inter annual variability. The same cyclones that transport cold, clean air from the Arctic to Europe will also transport warm polluted air in the other direction, which help cause the Arctic Haze phenomena. The cyclones have a key role for the atmospheric Aerosol life cycle in mid to high latitudes. Due to the observed growth to the size of CCN in one to two days, there is a potential feed back from the effects on the CCN population and cloud albedo even within the same weather system, but also on the climatic time scale.
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direct observational evidence linking atmospheric Aerosol Formation and cloud droplet activation
Geophysical Research Letters, 2005Co-Authors: Velimatti Kerminen, Heikki Lihavainen, Mika Komppula, Yrjo Viisanen, Markku KulmalaAbstract:[1] In order to predict the current state and future development of the Earth's climate system, detailed knowledge on how atmospheric Aerosol particles from various sources interact with clouds is needed. In this article we present, based on continuous Aerosol measurements in a remote continental location, direct observational evidence that Aerosol particles formed in the atmosphere from gaseous precursors eventually participate into cloud droplet activation. By combining the measurement data with theoretical calculations, we further demonstrate that the albedo of clouds may be significantly influenced by atmospheric Aerosol Formation, and that this process needs to be taken into account when estimating the indirect climatic effects of Aerosols in the global atmosphere.
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organic Aerosol Formation via sulphate cluster activation
Journal of Geophysical Research, 2004Co-Authors: Markku Kulmala, Velimatti Kerminen, T Anttila, Ari Laaksonen, Colin D OdowdAbstract:[1] The Formation of Aerosols, and subsequent cloud condensation nuclei, remains one of the least understood atmospheric processes upon which global climate change critically depends. Under atmospheric conditions, the process of homogeneous nucleation (Formation of stable clusters ∼ 1 nm in size), and their subsequent growth into new particles (>3 nm), determines the Aerosol and cloud nuclei population, yet, hitherto, no theory has elucidated the new particle Formation phenomenon in detail. In this study, we present a new theory which provides a mechanistic explanation for new particle Formation via activation of stable inorganic clusters by organic vapors. The new nano-particle activation theory is analogous to Kohler theory which describes cloud Formation in a supersaturated water vapor field but differs in that it describes the activation of inorganic stable nano-clusters into Aerosol particles in a supersaturated organic vapor which initiates spontaneous and rapid growth of clusters. Inclusion of the new theory into Aerosol Formation models predicts that increases in organic vapor densities lead to even greater increases in particle production, which, in turn, will influence the global radiative cooling effect of atmospheric Aerosols.
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secondary organic Aerosol Formation in the atmosphere via heterogeneous reaction of gaseous isoprene on acidic particles
Geophysical Research Letters, 2003Co-Authors: Andreas Limbeck, Markku Kulmala, Hans PuxbaumAbstract:[1] Water-soluble macromolecular substances with spectral properties of “humic-like substances” (HULIS) were recently found to form the major identified fraction of the organic Aerosol at urban and rural sites in Europe. With primary sources identified so far (e.g., biomass combustion) it is not possible to explain the observed HULIS levels in Europe, therefore there is an ongoing search for other sources - which form HULIS in situ in the atmosphere. Here we show that secondary Aerosol Formation of atmospheric polymers occurs by heterogeneous reaction of isoprenoid or terpenoid emissions in the presence of a sulfuric acid Aerosol catalyst. Competing oxidants such as ozone or the presence of humidity decreased the reaction yield, but the Formation of humic–like substances was not disabled. Calculations indicate that the presented reaction pathway could be an additional source for HULIS in the continental Aerosol.
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Marine Aerosol Formation from biogenic iodine emissions
Nature, 2002Co-Authors: Colin D. O'dowd, Roya Bahreini, Markku Kulmala, Jose L Jimenez, John H. Seinfeld, Kaarle Hameri, Liisa Pirjola, S. Gerard Jennings, Thorsten HoffmannAbstract:The Formation of marine Aerosols and cloud condensation nuclei—from which marine clouds originate—depends ultimately on the availability of new, nanometre-scale particles in the marine boundary layer. Because marine Aerosols and clouds scatter incoming radiation and contribute a cooling effect to the Earth's radiation budget^ 1 , new particle production is important in climate regulation. It has been suggested that sulphuric acid—derived from the oxidation of dimethyl sulphide—is responsible for the production of marine Aerosols and cloud condensation nuclei. It was accordingly proposed that algae producing dimethyl sulphide play a role in climate regulation^ 2 , but this has been difficult to prove and, consequently, the processes controlling marine particle Formation remains largely undetermined^ 3 , 4 . Here, using smog chamber experiments under coastal atmospheric conditions, we demonstrate that new particles can form from condensable iodine-containing vapours, which are the photolysis products of biogenic iodocarbons emitted from marine algae. Moreover, we illustrate, using Aerosol Formation models, that concentrations of condensable iodine-containing vapours over the open ocean are sufficient to influence marine particle Formation. We suggest therefore that marine iodocarbon emissions have a potentially significant effect on global radiative forcing.
John H. Seinfeld - One of the best experts on this subject based on the ideXlab platform.
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secondary organic Aerosol yields from the oxidation of benzyl alcohol
Atmospheric Chemistry and Physics, 2020Co-Authors: Sophia M Charan, Reina S Buenconsejo, John H. SeinfeldAbstract:Abstract. Recent inventory-based analysis suggests that emissions of volatile chemical products in urban areas are now competitive with those from the transportation sector. Understanding the potential for secondary organic Aerosol Formation from these volatile chemical products is, therefore, critical to predicting levels of Aerosol and for formulating policy to reduce Aerosol exposure. It is clear that a plethora of oxygenated compounds are either emitted directly into the atmosphere or emitted indoors and later escape into the outdoors. Experimental and computationally simulated environmental chamber data provide an understanding of Aerosol yield and chemistry under relevant urban conditions (5–200 ppb NO and 291–312 K) and give insight into the effect of volatile chemical products on the production of secondary organic Aerosol. Benzyl alcohol, one of these volatile chemical products, is found to have a large secondary organic Aerosol Formation potential. At NO concentrations of ~ 80 ppb and 291 K, secondary organic Aerosol mass yields for benzyl alcohol can reach 1.
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effect of acidity on secondary organic Aerosol Formation from isoprene
Environmental Science & Technology, 2007Co-Authors: J. D. Surratt, Michael Lewandowski, John H Offenberg, Mohammed Jaoui, Tadeusz E Kleindienst, Edward O Edney, John H. SeinfeldAbstract:The effect of particle-phase acidity on secondary organic Aerosol (SOA) Formation from isoprene is investigated in a laboratory chamber study, in which the acidity of the inorganic seed Aerosol was controlled systematically. The observed enhancement in SOA mass concentration is closely correlated to increasing Aerosol acidity (R2 = 0.979). Direct chemical evidence for acid-catalyzed particle-phase reactions was obtained from the SOA chemical analyses. Aerosol mass concentrations for the 2-methyltetrols, as well as the newly identified sulfate esters, both of which serve as tracers for isoprene SOA in ambient Aerosols, increased significantly with enhanced Aerosol acidity. Aerosol acidities, as measured in nmol of H+ m-3, employed in the present study are in the same range as those observed in tropospheric Aerosol collected from the eastern U.S.
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secondary organic Aerosol Formation from isoprene photooxidation
Environmental Science & Technology, 2006Co-Authors: Jesse H Kroll, Richard C Flagan, S. M. Murphy, John H. SeinfeldAbstract:Recent work has shown that the atmospheric oxidation of isoprene (2-methyl-1,3-butadiene, C5H8) leads to the Formation of secondary organic Aerosol (SOA). In this study, the mechanism of SOA Formation by isoprene photooxidation is comprehensively investigated, by measurements of SOA yields over a range of experimental conditions, namely isoprene and NOx concentrations. Hydrogen peroxide is used as the radical precursor, substantially constraining the observed gas-phase chemistry; all oxidation is dominated by the OH radical, and organic peroxy radicals (RO2) react only with HO2 (formed in the OH + H2O2 reaction) or NO concentrations, including NOx-free conditions. At high NOx, yields are found to decrease substantially with increasing [NOx], indicating the importance of RO2 chemistry in SOA Formation. Under low-NOx conditions, SOA mass is observed to decay rapidly, a result of chemical reactions of semivolatile SOA components, most likely organic hydroperoxides.
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Marine Aerosol Formation from biogenic iodine emissions
Nature, 2002Co-Authors: Colin D. O'dowd, Roya Bahreini, Markku Kulmala, Jose L Jimenez, John H. Seinfeld, Kaarle Hameri, Liisa Pirjola, S. Gerard Jennings, Thorsten HoffmannAbstract:The Formation of marine Aerosols and cloud condensation nuclei—from which marine clouds originate—depends ultimately on the availability of new, nanometre-scale particles in the marine boundary layer. Because marine Aerosols and clouds scatter incoming radiation and contribute a cooling effect to the Earth's radiation budget^ 1 , new particle production is important in climate regulation. It has been suggested that sulphuric acid—derived from the oxidation of dimethyl sulphide—is responsible for the production of marine Aerosols and cloud condensation nuclei. It was accordingly proposed that algae producing dimethyl sulphide play a role in climate regulation^ 2 , but this has been difficult to prove and, consequently, the processes controlling marine particle Formation remains largely undetermined^ 3 , 4 . Here, using smog chamber experiments under coastal atmospheric conditions, we demonstrate that new particles can form from condensable iodine-containing vapours, which are the photolysis products of biogenic iodocarbons emitted from marine algae. Moreover, we illustrate, using Aerosol Formation models, that concentrations of condensable iodine-containing vapours over the open ocean are sufficient to influence marine particle Formation. We suggest therefore that marine iodocarbon emissions have a potentially significant effect on global radiative forcing.
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state of the art chamber facility for studying atmospheric Aerosol chemistry
Environmental Science & Technology, 2001Co-Authors: David R Cocker, Richard C Flagan, John H. SeinfeldAbstract:A state-of-the-art chamber facility is described for investigation of atmospheric Aerosol chemistry. Dual 28 m^3 FEP Teflon film chambers are used to simulate atmospheric conditions in which Aerosol Formation may occur. This facility provides the flexibility to investigate dark, single oxidant reactions as well as full photochemical simulations. This paper discusses the environmental control implemented as well as the gas-phase and Aerosol-phase instrumentation used to monitor atmospheric Aerosol Formation and growth. Physical processes occurring in the chamber and procedures for estimating secondary organic Aerosol Formation during reaction are described. Aerosol Formation and evolution protocols at varying relative humidity conditions are presented.
Jozef Peeters - One of the best experts on this subject based on the ideXlab platform.
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modeling Aerosol Formation in alpha pinene photo oxidation experiments
Journal of Geophysical Research, 2008Co-Authors: M Capouet, Luc Vereecken, J F Muller, K Ceulemans, Steven Compernolle, Jozef PeetersAbstract:[1] We present BOREAM (Biogenic hydrocarbon Oxidation and Related Aerosol Formation Model), a detailed model for the oxidation of α-pinene and the resulting Formation of secondary organic Aerosol (SOA). It is based on a quasi-explicit gas phase mechanism for the Formation of primary products, developed on objective grounds using advanced theoretical methods, and on a simplified representation for the further oxidation of the products. The partitioning of the products follows a kinetic representation with coefficients estimated from vapor pressures calculated using a dedicated group contribution method. Particle phase and heterogeneous reactions are generally neglected, but the impact of peroxyhemiacetal Formation in the Aerosol is tested on the basis of laboratory estimates of the reaction rates. The model is evaluated against 28 laboratory experiments from 6 studies of α-pinene photo-oxidation covering a wide range of photochemical conditions. In contrast with previous modeling studies, the modeled and measured SOA yields agree to within a factor of 2 in most cases. The SOA yields are underestimated for the ozonolysis experiments of Presto et al. (2005a) when the standard version of the ozonolysis mechanism is used, presumably because of the lack of credible pathways for the Formation of pinic and hydroxy pinonic acid. The underestimation is drastically reduced when the mechanism is modified to account for the Formation of these compounds. Accounting for peroxyhemiacetal Formation in the particle phase is found to further increase the SOA yields by about one third in high VOC ozonolysis experiments and to have a much smaller impact in all other cases. The model calculates that ozonolysis contributes about twice more to SOA Formation than oxidation by OH, whereas NO3-initiated oxidation is negligible. In agreement with previous studies, low NOx conditions and low temperatures are calculated to favor Aerosol Formation, but the estimated temperature dependence is stronger than found in recent laboratory experiments.
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modeling Aerosol Formation in alpha pinene photo oxidation experiments
Journal of Geophysical Research, 2008Co-Authors: M Capouet, Luc Vereecken, K Ceulemans, Steven Compernolle, Jeanfrancois Muller, Jozef PeetersAbstract:[1] We present BOREAM (Biogenic hydrocarbon Oxidation and Related Aerosol Formation Model), a detailed model for the oxidation of α-pinene and the resulting Formation of secondary organic Aerosol (SOA). It is based on a quasi-explicit gas phase mechanism for the Formation of primary products, developed on objective grounds using advanced theoretical methods, and on a simplified representation for the further oxidation of the products. The partitioning of the products follows a kinetic representation with coefficients estimated from vapor pressures calculated using a dedicated group contribution method. Particle phase and heterogeneous reactions are generally neglected, but the impact of peroxyhemiacetal Formation in the Aerosol is tested on the basis of laboratory estimates of the reaction rates. The model is evaluated against 28 laboratory experiments from 6 studies of α-pinene photo-oxidation covering a wide range of photochemical conditions. In contrast with previous modeling studies, the modeled and measured SOA yields agree to within a factor of 2 in most cases. The SOA yields are underestimated for the ozonolysis experiments of Presto et al. (2005a) when the standard version of the ozonolysis mechanism is used, presumably because of the lack of credible pathways for the Formation of pinic and hydroxy pinonic acid. The underestimation is drastically reduced when the mechanism is modified to account for the Formation of these compounds. Accounting for peroxyhemiacetal Formation in the particle phase is found to further increase the SOA yields by about one third in high VOC ozonolysis experiments and to have a much smaller impact in all other cases. The model calculates that ozonolysis contributes about twice more to SOA Formation than oxidation by OH, whereas NO3-initiated oxidation is negligible. In agreement with previous studies, low NOx conditions and low temperatures are calculated to favor Aerosol Formation, but the estimated temperature dependence is stronger than found in recent laboratory experiments.
Colin D Odowd - One of the best experts on this subject based on the ideXlab platform.
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marine Aerosol production a review of the current knowledge
Philosophical Transactions of the Royal Society A, 2007Co-Authors: Colin D Odowd, Gerrit De LeeuwAbstract:The current knowledge in primary and secondary marine Aerosol Formation is reviewed. For primary marine Aerosol source functions, recent source functions have demonstrated a significant flux of submicrometre particles down to radii of 20 nm. Moreover, the source functions derived from different techniques up to 10 mm have come within a factor of two of each other. For secondary marine Aerosol Formation, recent advances have identified iodine oxides and isoprene oxidation products, in addition to sulphuric acid, as contributing to Formation and growth, although the exact roles remains to be determined. While a multistep process seems to be required, isoprene oxidation products are more likely to participate in growth and sulphuric acid is more likely to participate in nucleation. Iodine oxides are likely to participate in both nucleation and growth.
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organic Aerosol Formation via sulphate cluster activation
Journal of Geophysical Research, 2004Co-Authors: Markku Kulmala, Velimatti Kerminen, T Anttila, Ari Laaksonen, Colin D OdowdAbstract:[1] The Formation of Aerosols, and subsequent cloud condensation nuclei, remains one of the least understood atmospheric processes upon which global climate change critically depends. Under atmospheric conditions, the process of homogeneous nucleation (Formation of stable clusters ∼ 1 nm in size), and their subsequent growth into new particles (>3 nm), determines the Aerosol and cloud nuclei population, yet, hitherto, no theory has elucidated the new particle Formation phenomenon in detail. In this study, we present a new theory which provides a mechanistic explanation for new particle Formation via activation of stable inorganic clusters by organic vapors. The new nano-particle activation theory is analogous to Kohler theory which describes cloud Formation in a supersaturated water vapor field but differs in that it describes the activation of inorganic stable nano-clusters into Aerosol particles in a supersaturated organic vapor which initiates spontaneous and rapid growth of clusters. Inclusion of the new theory into Aerosol Formation models predicts that increases in organic vapor densities lead to even greater increases in particle production, which, in turn, will influence the global radiative cooling effect of atmospheric Aerosols.
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Aerosol Formation atmospheric particles from organic vapours
Nature, 2002Co-Authors: Colin D Odowd, Markku Kulmala, Pasi Aalto, Kaarle Hmeri, Thorsten HoffmannAbstract:Aerosol particles produced over forested areas may affect climate by acting as nuclei for cloud condensation, but their composition (and hence the chemical species that drive their production) remains an open question. Here we show, to our knowledge for the first time, that these newly formed particles (3–5 nm in diameter) are composed primarily of organic species, such as cis-pinonic acid and pinic acid, produced by oxidation of terpenes in organic vapours released from the canopy1,2,3,4.
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effects of continental boundary layer evolution convection turbulence and entrainment on Aerosol Formation
Tellus B, 2001Co-Authors: E D Nilsson, Colin D Odowd, Markku Kulmala, G Buzorius, Ullar RannikAbstract:Aerosol nucleation events occurring in the continental boundary layer over the boreal forest region in Finland, during the BIOFOR experiment, have been examined to elucidate the role of micrometeorology in promoting such events. Invariably, during the spring campaign of 1999, nucleation events occurred in Arctic and polar air masses during cold air outbreaks. Under clear-sky conditions, typical of these synoptic meteorological patterns, the boundary layer evolution was characterized by the rapid growth of a mixed layer, convection and strong entrainment, first from the residual later and later from the free troposphere. It was found that the freshly nucleated particles were detected within two hours from the onset of strong turbulent kinetic energy, independent of how fast the boundary layer evolved. When considering the growth time from cluster size of ≈ 1 nm to detectable sizes of 3 nm, the nucleation and onset of strong turbulence coincided almost exactly. The most likely site for nucleation to take place was the mixed layer or the entrainment zone, while the forest canopy and the free troposphere could be excluded as the nucleation region. There are several possible explanations for the correlation between the onset of turbulence and nucleation: (1) new Aerosols or clusters may have been entrained from the residual layer into the mixed layer where they then (in the case of clusters) underwent growth to detectable sizes; (2) two or more precursor gases may have been mixed with each other over the entrainment zone; (3) the adiabatic cooling in the rising convective plumes and the turbulent fluctuation in temperature and vapors by the entrainment flux may have enhanced Aerosol Formation; (4) a sudden decrease in preexisting Aerosol due to dilution of the mixed layer Aerosol by entrained air may have reduced the vapor sink enough to initiate nucleation. However, the lack of vertical profile measurements of nucleation mode Aerosols, precursor vapors and turbulent fluctuations throughout and above the mixed-layer results in it remaining an open question as to which one of these processes dominates. DOI: 10.1034/j.1600-0889.2001.530409.x