CCN closure study: Effects of aerosol chemical composition and mixing state

TL;DR: In this article, the effects of chemical composition (bulk and size resolved) and mixing state (internal and external) on CCN activity of aerosols were investigated during the winter season in Kanpur.

Abstract: This study presents a detailed cloud condensation nuclei (CCN) closure study that investigates the effects of chemical composition (bulk and size resolved) and mixing state (internal and external) on CCN activity of aerosols. Measurements of the chemical composition, aerosol size distribution, total number concentration, and CCN concentration at supersaturation (SS = 0.2–1.0%) were performed during the winter season in Kanpur, India. Among the two cases considered here, better closure results are obtained for case 1 (low total aerosol loading, 49.54 ± 26.42 μg m−3, and high O:C ratio, 0.61 ± 0.07) compared to case 2 (high total aerosol loading, 101.05 ± 18.73 μg m−3, and low O:C ratio, 0.42 ± 0.06), with a maximum reduction of 3–81% in CCN overprediction for all depleted SS values (0.18–0.60%). Including the assumption that less volatile oxidized organic aerosols represent the soluble organic fraction reduced the overprediction to at most 40% and 129% in the internal and external mixing scenarios, respectively. At higher depleted SS values (0.34–0.60%), size-resolved chemical composition with an internal mixing state performed well in CCN closure among all organic solubility scenarios. However, at a lower depleted SS value (0.18%), closure is found to be more sensitive to both the chemical composition and mixing state of aerosols. At higher SS values, information on the solubility of organics and size-resolved chemical composition is required for accurate CCN predictions, whereas at lower SS values, information on the mixing state in addition to the solubility of organics and size-resolved chemical composition is required. Overall, κtotal values are observed to be independent of the O:C ratio [κtotal = (0.36 ± 0.01) × O:C − (0.03 ± 0.01)] in the range of 0.2

TL;DR: In this paper, a comparison of measurements collected by the US Department of Energy Gulfstream-1 (G1) and the German High Altitude and Long-Range Research Aircraft (HALO) during three coordinated flights on 9 and 21 September 2014 and 1 and 1 October 2014 is presented.

Abstract: . The indirect effect of atmospheric aerosol particles on the Earth's radiation balance remains one of the most uncertain components affecting climate change throughout the industrial period. The large uncertainty is partly due to the incomplete understanding of aerosol–cloud interactions. One objective of the GoAmazon2014/5 and the ACRIDICON (Aerosol, Cloud, Precipitation, and Radiation Interactions and Dynamics of Convective Cloud Systems)-CHUVA (Cloud Processes of the Main Precipitation Systems in Brazil) projects was to understand the influence of emissions from the tropical megacity of Manaus (Brazil) on the surrounding atmospheric environment of the rainforest and to investigate its role in the life cycle of convective clouds. During one of the intensive observation periods (IOPs) in the dry season from 1 September to 10 October 2014, comprehensive measurements of trace gases and aerosol properties were carried out at several ground sites. In a coordinated way, the advanced suites of sophisticated in situ instruments were deployed aboard both the US Department of Energy Gulfstream-1 (G1) aircraft and the German High Altitude and Long-Range Research Aircraft (HALO) during three coordinated flights on 9 and 21 September and 1 October. Here, we report on the comparison of measurements collected by the two aircraft during these three flights. Such comparisons are challenging but essential for assessing the data quality from the individual platforms and quantifying their uncertainty sources. Similar instruments mounted on the G1 and HALO collected vertical profile measurements of aerosol particle number concentrations and size distribution, cloud condensation nuclei concentrations, ozone and carbon monoxide mixing ratios, cloud droplet size distributions, and downward solar irradiance. We find that the above measurements from the two aircraft agreed within the measurement uncertainties. The relative fraction of the aerosol chemical composition measured by instruments on HALO agreed with the corresponding G1 data, although the total mass loadings only have a good agreement at high altitudes. Furthermore, possible causes of the discrepancies between measurements on the G1 and HALO are examined in this paper. Based on these results, criteria for meaningful aircraft measurement comparisons are discussed.

TL;DR: In this paper, the authors performed a continuous aerosol and cloud condensation nuclei (CCN) measurements carried out at an observational facility situated in the rain-shadow region of the Indian subcontinent during the Indian summer monsoon season (June to September) of 2018.

Abstract: Continuous aerosol and cloud condensation nuclei (CCN) measurements carried out at the ground observational facility situated in the rain-shadow region of the Indian subcontinent are illustrated These observations were part of the Cloud Aerosol Interaction Precipitation Enhancement Experiment (CAIPEEX) during the Indian summer monsoon season (June to September) of 2018 Observations are classified as dry–continental (monsoon break) and wet–marine (monsoon active) according to the air mass history CCN concentrations measured for a range of supersaturations (02 %–12 %) are parameterized using Twomey's empirical relationship CCN concentrations at low (02 %) supersaturation (SS) were high ( > 1000 cm - 3 ) during continental conditions and observed together with high black carbon ( BC ∼ 2000 ng m - 3 ) and columnar aerosol loading During the marine air mass conditions, CCN concentrations diminished to ∼ 350 cm - 3 at 03 % SS and low aerosol loading persisted ( BC ∼ 800 ng m - 3 ) High CCN activation fraction (AF) of ≅055 (at 03 % SS) was observed before the monsoon rainfall, which reduced to ≅015 during the marine air mass and enhanced to ≅032 after that There was mostly monomodal aerosol number size distribution (NSD) with a mean geometric mean diameter (GMD) of ≅85 nm , with least ( ≅9 %) contribution from nucleation mode ( nm ) particles persisted before the monsoon, while multimode NSD with ≅19 % of nucleation mode particles was found during the marine air mass Critical activation diameters ( dcri ) for 03 % SS were found to be about 72, 169, and 121 nm prior to, during, and after the marine conditions, respectively The better association of CCN with aerosol absorption, and the concurrent accumulation mode particles during continental conditions, points to the possibility of aged (oxygenated) carbonaceous aerosols enhancing the CCN activity prior to the marine conditions An enhancement in CCN concentrations and k values during the daytime along with absorption Angstrom exponent was observed during the marine conditions Best closure obtained using measured critical diameter and ammonium sulfate composition during continental conditions emphasizes the role of aged aerosols contributing to the accumulation mode, enhancing the CCN efficiency The overestimation of CCN and less hygroscopicity of accumulation mode aerosols during the marine air mass indicate the role of size-dependent aerosol composition in CCN activity during the period

TL;DR: In this paper, the authors highlight the first multiweek size-resolved analysis of high-resolution (HR) mass spectra from the Aerodyne aerosol mass spectrometer (AMS).

Abstract: This work highlights the first multiweek size-resolved analysis of high-resolution (HR) mass spectra from the Aerodyne aerosol mass spectrometer (AMS). High-resolution analysis allows for separatio...

TL;DR: In this article, a Droplet Measurement Technology (DMT) Cloud Condensation Nuclei Counter (CCNC) was deployed to measure cloud condensation nuclei (CCN) for the first time in the pristine Himalayan region at Himalayan Clouds Observatory (HCO), Swami Ram Tirtha (SRT) Campus (30°34′ N, 78°41′ E, 1706m AMSL), Hemvati Nandan Bahuguna (HNB) Garhwal University, Badshahithaul, Tehri Garhway

TL;DR: In this article, a nouvelle methodologie d'analyse des aerosols inorganiques, a basse temperature, par cryo-microscopie electronique (cryo-TSEM-EDX) a ete mise au point.

Abstract: Lors de leur sejour dans l’atmosphere, les aerosols sont soumis, entre autres, a des processus d’agregation, ainsi que de condensation sur leurs surfaces. Ces processus, dit de vieillissement, dependent du temps de residence des particules dans l’atmosphere, des conditions meteorologiques et de l’environnement chimique rencontre. Cette etude vise a caracteriser l’aerosol inorganique et etudier son evolution physico-chimique sur quelques dizaines de milliers de metres, dans les panaches industriels et urbains ou les concentrations atmospheriques en particules fines (PM₁₀) sont relativement elevees. Il s’agit notamment de rendre compte de l’evolution des particules d’aerosol primaire lors d’episodes de formation d’aerosols secondaires inorganiques.Dans ce cadre, dans un premier temps, une nouvelle methodologie d’analyse des aerosols inorganiques, a basse temperature, par cryo-microscopie electronique (cryo-TSEM-EDX) a ete mise au point. L’enjeu etait notamment de rendre compte de l’etat de melange des composes atmospheriques d’origine secondaire (composes semi-volatils), avec l’aerosol primaire. Ces developpements analytiques ont tout d’abord ete realises a l’aide de composes modeles, avant d’etre valides sur particules environnementales. Dans un second temps, l’etude des processus physico-chimiques mis en jeu lors du vieillissement des aerosols, a l’echelle locale (quelques kilometres), a ete realisee au cours d’une campagne intensive de terrain sur le dunkerquois, visant a etudier plus particulierement l’evolution des emissions industrielles en milieu urbain. Des prelevements ont ainsi ete realises en bordure de zone industrielle et sur de sites "recepteurs" sous l’influence potentielle des emissions industrielles. Les analyses realisees sur ces particules par cryo-SEM-EDX ont notamment montre qu’en zone peri-urbaine, a quelques kilometres de la zone industrielle, des particules emises par la siderurgie, comme les oxydes de fer, evoluaient rapidement, pour se retrouver, en melange interne, associes a de la matiere organique particulaire. En parallele, nous avons pu caracteriser, sur ces sites recepteurs, la presence d’aerosols inorganiques secondaires absents de la zone source et donc formes au sein de l’air ambiant, lors du survol de l’agglomeration dunkerquoise.

TL;DR: The aerosol forcing has likely offset global greenhouse warming to a substantial degree, however, differences in geographical and seasonal distributions of these forcings preclude any simple compensation.

Abstract: Although long considered to be of marginal importance to global climate change, tropospheric aerosol contributes substantially to radiative forcing, and anthropogenic sulfate aerosol in particular has imposed a major perturbation to this forcing. Both the direct scattering of shortwavelength solar radiation and the modification of the shortwave reflective properties of clouds by sulfate aerosol particles increase planetary albedo, thereby exerting a cooling influence on the planet. Current climate forcing due to anthropogenic sulfate is estimated to be –1 to –2 watts per square meter, globally averaged. This perturbation is comparable in magnitude to current anthropogenic greenhouse gas forcing but opposite in sign. Thus, the aerosol forcing has likely offset global greenhouse warming to a substantial degree. However, differences in geographical and seasonal distributions of these forcings preclude any simple compensation. Aerosol effects must be taken into account in evaluating anthropogenic influences on past, current, and projected future climate and in formulating policy regarding controls on emission of greenhouse gases and sulfur dioxide. Resolution of such policy issues requires integrated research on the magnitude and geographical distribution of aerosol climate forcing and on the controlling chemical and physical processes.

TL;DR: In this article, an overview of the atmospheric degradation mechanisms for SOA precursors, gas-particle partitioning theory and analytical techniques used to determine the chemical composition of SOA is presented.

Abstract: Secondary organic aerosol (SOA) accounts for a significant fraction of ambient tropospheric aerosol and a detailed knowledge of the formation, properties and transformation of SOA is therefore required to evaluate its impact on atmospheric processes, climate and human health. The chemical and physical processes associated with SOA formation are complex and varied, and, despite considerable progress in recent years, a quantitative and predictive understanding of SOA formation does not exist and therefore represents a major research challenge in atmospheric science. This review begins with an update on the current state of knowledge on the global SOA budget and is followed by an overview of the atmospheric degradation mechanisms for SOA precursors, gas-particle partitioning theory and the analytical techniques used to determine the chemical composition of SOA. A survey of recent laboratory, field and modeling studies is also presented. The following topical and emerging issues are highlighted and discussed in detail: molecular characterization of biogenic SOA constituents, condensed phase reactions and oligomerization, the interaction of atmospheric organic components with sulfuric acid, the chemical and photochemical processing of organics in the atmospheric aqueous phase, aerosol formation from real plant emissions, interaction of atmospheric organic components with water, thermodynamics and mixtures in atmospheric models. Finally, the major challenges ahead in laboratory, field and modeling studies of SOA are discussed and recommendations for future research directions are proposed.

TL;DR: A unifying model framework describing the atmospheric evolution of OA that is constrained by high–time-resolution measurements of its composition, volatility, and oxidation state is presented, which can serve as a basis for improving parameterizations in regional and global models.

Abstract: Organic aerosol (OA) particles affect climate forcing and human health, but their sources and evolution remain poorly characterized. We present a unifying model framework describing the atmospheric evolution of OA that is constrained by high-time-resolution measurements of its composition, volatility, and oxidation state. OA and OA precursor gases evolve by becoming increasingly oxidized, less volatile, and more hygroscopic, leading to the formation of oxygenated organic aerosol (OOA), with concentrations comparable to those of sulfate aerosol throughout the Northern Hemisphere. Our model framework captures the dynamic aging behavior observed in both the atmosphere and laboratory: It can serve as a basis for improving parameterizations in regional and global models.

TL;DR: In this article, the authors reviewed existing knowledge with regard to organic aerosol (OA) of importance for global climate modelling and defined critical gaps needed to reduce the involved uncertainties, and synthesized the information to provide a continuous analysis of the flow from the emitted material to the atmosphere up to the point of the climate impact of the produced organic aerosols.

Abstract: The present paper reviews existing knowledge with regard to Organic Aerosol (OA) of importance for global climate modelling and defines critical gaps needed to reduce the involved uncertainties. All pieces required for the representation of OA in a global climate model are sketched out with special attention to Secondary Organic Aerosol (SOA): The emission estimates of primary carbonaceous particles and SOA precursor gases are summarized. The up-to-date understanding of the chemical formation and transformation of condensable organic material is outlined. Knowledge on the hygroscopicity of OA and measurements of optical properties of the organic aerosol constituents are summarized. The mechanisms of interactions of OA with clouds and dry and wet removal processes parameterisations in global models are outlined. This information is synthesized to provide a continuous analysis of the flow from the emitted material to the atmosphere up to the point of the climate impact of the produced organic aerosol. The sources of uncertainties at each step of this process are highlighted as areas that require further studies.

TL;DR: In this paper, a method to describe the relationship between particle dry diameter and cloud condensation activity using a single hygroscopicity parameter is presented. But this method is limited to single and multi-component particles with varying amounts of inorganic, organic and surface active compounds.

Abstract: We present a method to describe the relationship between particle dry diameter and cloud condensation nu- clei (CCN) activity using a single hygroscopicity parameter . Values of the hygroscopicity parameter are between 0.5 and 1.4 for highly-CCN-active salts such as sodium chlo- ride, between 0.01 and 0.5 for slightly to very hygroscopic organic species, and 0 for nonhygroscopic components. Ob- servations indicate that atmospheric particulate matter is typ- ically characterized by 0.1<< 0.9. If compositional data are available and if the hygroscopicity parameter of each com- ponent is known, a multicomponent hygroscopicity parame- ter can be computed by weighting component hygroscopic- ity parameters by their volume fractions in the mixture. In the absence of information on chemical composition, exper- imental data for complex, multicomponent particles can be fitted to obtain the hygroscopicity parameter. The hygroscop- icity parameter can thus also be used to conveniently model the CCN activity of atmospheric particles, including those containing insoluble components. We confirm the applica- bility of the hygroscopicity parameter and its mixing rule by applying it to published hygroscopic diameter growth fac- tor and CCN-activation data for single- and multi-component particles containing varying amounts of inorganic, organic and surface active compounds. We suggest that may be fit to CCN data assuming s/a=0.072 J m 2 and present a table of derived for this value and T=298.15 K. The predicted hygroscopicities for mixtures that contain the surfactant ful- vic acid agree within uncertainties with the measured values. It thus appears that this approach is adequate for predict- ing CCN activity of mixed particles containing surface ac- tive materials, but the generality of this assumption requires further verification.