Calibration and measurement uncertainties of a continuous-flow cloud condensation nuclei counter (DMT-CCNC): CCN activation of ammonium sulfate and sodium chloride aerosol particles in theory and experiment

International audienceExperimental and theoretical uncertainties in the measurement of cloud condensation nuclei (CCN) with a continuous-flow thermal-gradient CCN counter from Droplet Measurement Technologies (DMT-CCNC) have been assessed by model calculations and calibration experiments with ammonium sulfate and sodium chloride aerosol particles in the diameter range of 20?220 nm. Experiments have been performed in the laboratory and during field measurement campaigns, extending over a period of more than one year and covering a wide range of operating conditions (650?1020 hPa ambient pressure, 0.5?1.0 L min?1 aerosol flow rate, 20?30°C inlet temperature, 4?34 K m?1 temperature gradient). For each set of conditions, the effective water vapor supersaturation (Seff) in the CCNC was determined from the measured CCN activation spectra and Köhler model calculations. High measurement precision was achieved under stable laboratory conditions, where relative variations of Seff in the CCNC were generally less than ±2%. During field measurements, however, the relative variability increased up to ±5?7%, which can be mostly attributed to variations of the CCNC column top temperature with ambient temperature. To assess the accuracy of the Köhler models used to calculate Seff, we have performed a comprehensive comparison and uncertainty analysis of the various Köhler models and thermodynamic parameterizations commonly used in CCN studies. For the relevant supersaturation range (0.05?2%), the relative deviations between different modeling approaches were as high as 25% for (NH4)2SO4 and 16% for NaCl. The deviations were mostly caused by the different parameterizations for the activity of water in aqueous solutions of (NH4)2SO4 and NaCl (activity parameterization, osmotic coefficient, and van't Hoff factor models). The uncertainties related to the model parameterizations of water activity clearly exceeded the CCNC measurement precision. Relative deviations caused by different ways of calculating or approximating solution density and surface tension did not exceed 3% for (NH4)2SO4 and 1.5% for NaCl. Nevertheless, they did exceed the CCNC measurement precision under well-defined operating conditions and should not be neglected in studies aimed at high accuracy. To ensure comparability of results, we suggest that CCN studies should always report exactly which Köhler model equations and parameterizations of solution properties were used. Substantial differences between the CCNC calibration results obtained with (NH4)2SO4 and NaCl aerosols under equal experimental conditions (relative deviations of Seff up to ~10%) indicate inconsistencies between widely used activity parameterizations derived from electrodynamic balance (EDB) single particle experiments (Tang and Munkelwitz, 1994; Tang, 1996) and hygroscopicity tandem differential mobility analyzer (HTDMA) aerosol experiments (Kreidenweis et al., 2005). Therefore, we see a need for further evaluation and experimental confirmation of preferred data sets and parameterizations for the activity of water in dilute aqueous (NH4)2SO4 and NaCl solutions. The experimental results were also used to test the CCNC flow model of Lance et al.~(2006), which describes the dependence of Seff on temperature, pressure, and flow rate in the CCN counter. This model could be applied after subtraction of a near-constant temperature offset and derivation of an instrument-specific thermal resistance parameter (RT?1.8 K W?1). At Seff>0.1% the relative deviations between the flow model and experimental results were mostly less than 5%, when the same Köhler model approach was used. At Seff?.1%, however, the deviations exceeded 20%, which can be attributed to non-idealities which also caused the near-constant temperature offset. Therefore, we suggest that the CCNC flow model can be used to extrapolate calibration results, but should generally be complemented by calibration experiments performed under the relevant operating conditions ? during field campaigns as well as in laboratory studies

Cloud condensation nuclei in pristine tropical rainforest air of Amazonia: size-resolved measurements and modeling of atmospheric aerosol composition and CCN activity

Atmospheric aerosol particles serving as cloud condensation nuclei (CCN) are key elements of the hydrological cycle and climate. We have measured and characterized CCN at water vapor supersaturations in the range of <i>S</i>=0.10–0.82% in pristine tropical rainforest air during the AMAZE-08 campaign in central Amazonia. <br><br> The effective hygroscopicity parameters describing the influence of chemical composition on the CCN activity of aerosol particles varied in the range of &kappa;&asymp;0.1–0.4 (0.16&plusmn;0.06 arithmetic mean and standard deviation). The overall median value of &kappa;&asymp;0.15 was by a factor of two lower than the values typically observed for continental aerosols in other regions of the world. Aitken mode particles were less hygroscopic than accumulation mode particles (&kappa;&asymp;0.1 at <i>D</i>&asymp;50 nm; &kappa;&asymp;0.2 at <i>D</i>&asymp;200 nm), which is in agreement with earlier hygroscopicity tandem differential mobility analyzer (H-TDMA) studies. <br><br> The CCN measurement results are consistent with aerosol mass spectrometry (AMS) data, showing that the organic mass fraction (<i>f</i>_org) was on average as high as ~90% in the Aitken mode (<i>D</i>&le;100 nm) and decreased with increasing particle diameter in the accumulation mode (~80% at <i>D</i>&asymp;200 nm). The κ values exhibited a negative linear correlation with <i>f</i>_org (<i>R</i>²=0.81), and extrapolation yielded the following effective hygroscopicity parameters for organic and inorganic particle components: &kappa;_org&asymp;0.1 which can be regarded as the effective hygroscopicity of biogenic secondary organic aerosol (SOA) and &kappa;_inorg&asymp;0.6 which is characteristic for ammonium sulfate and related salts. Both the size dependence and the temporal variability of effective particle hygroscopicity could be parameterized as a function of AMS-based organic and inorganic mass fractions (&kappa;_p=&kappa;_org&times;<i>f</i>_org +&kappa;_inorg&times;<i>f</i>_inorg). The CCN number concentrations predicted with &kappa;_p were in fair agreement with the measurement results (~20% average deviation). The median CCN number concentrations at <i>S</i>=0.1–0.82% ranged from <i>N</i>_CCN,0.10&asymp;35 cm^&minus;3 to <i>N</i>_CCN,0.82&asymp;160 cm^&minus;3, the median concentration of aerosol particles larger than 30 nm was <i>N</i>_CN,30&asymp;200 cm^&minus;3, and the corresponding integral CCN efficiencies were in the range of <i>N</i>_CCN,0.10/<i>N</i>_CN,30&asymp;0.1 to <i>N</i>_CCN,0.82/<i>N</i>_CN,30&asymp;0.8. <br><br> Although the number concentrations and hygroscopicity parameters were much lower in pristine rainforest air, the integral CCN efficiencies observed were similar to those in highly polluted megacity air. Moreover, model calculations of <i>N</i>_CCN,<i>S</i> assuming an approximate global average value of &kappa;&asymp;0.3 for continental aerosols led to systematic overpredictions, but the average deviations exceeded ~50% only at low water vapor supersaturation (0.1%) and low particle number concentrations (&le;100 cm^&minus;3). Model calculations assuming a constant aerosol size distribution led to higher average deviations at all investigated levels of supersaturation: ~60% for the campaign average distribution and ~1600% for a generic remote continental size distribution. These findings confirm earlier studies suggesting that aerosol particle number and size are the major predictors for the variability of the CCN concentration in continental boundary layer air, followed by particle composition and hygroscopicity as relatively minor modulators. <br><br> Depending on the required and applicable level of detail, the information and parameterizations presented in this paper should enable efficient description of the CCN properties of pristine tropical rainforest aerosols of Amazonia in detailed process models as well as in large-scale atmospheric and climate models

Seasonal Variability in Fine Particulate Matter Water Content and Estimated pH over a Coastal Region in the Northeast Arabian Sea

The acidity of atmospheric particles can promote specific chemical processes that result in the production of extra condensed phases from lesser volatile species (secondary fine particulate matter), change the optical and water absorption characteristics of particles, and enhance trace metal solubility that can function as essential nutrients in nutrient-limited environments. In this study, we present an estimated pH of fine particulate matter (FPM) through a thermodynamic model and assess its temporal variability over a coastal location in the northeast Arabian Sea. Here, we have used the chemical composition of FPM (PM2.5) collected during the period between 2017–2019. Chemical composition data showed large variability in water-soluble ionic concentrations (WSIC; range: 2.3–39.9 μg m−3) with higher and lower average values during the winter and summer months, respectively. SO42− ions were predominant among anions, while NH4+ was a major contributor among cations throughout the season. The estimated pH of FPM from the forward and reverse modes exhibits a moderate correlation for winter and summer samples. The estimated pH of FPM is largely regulated by SO42− content and strongly depends on the relative ambient humidity, particularly in the forward mode. Major sources of FPM assessed based on Positive matrix factorization (PMF) and air-mass back trajectory analyses demonstrate the dominance of natural sources (sea salt and dust) during summer months, anthropogenic sources in winter months and mixed sources during the post-monsoon season

Cloud condensation nuclei (CCN) from fresh and aged air pollution in the megacity region of Beijing

Atmospheric aerosol particles serving as cloud condensation nuclei (CCN) are key elements of the hydrological cycle and climate. CCN properties were measured and characterized during the CAREBeijing-2006 campaign at a regional site south of the megacity of Beijing, China. Size-resolved CCN efficiency spectra recorded for a supersaturation range of &lt;i&gt;S&lt;/i&gt;=0.07% to 0.86% yielded average activation diameters in the range of 190 nm to 45 nm. The corresponding effective hygroscopicity parameters (&amp;kappa;) exhibited a strong size dependence ranging from ~0.25 in the Aitken size range to ~0.45 in the accumulation size range. The campaign average value (&amp;kappa; =0.3 ± 0.1) was similar to the values observed and modeled for other populated continental regions. &lt;br&gt;&lt;br&gt; The hygroscopicity parameters derived from the CCN measurements were consistent with chemical composition data recorded by an aerosol mass spectrometer (AMS) and thermo-optical measurements of apparent elemental and organic carbon (EC and OC). The CCN hygroscopicity and its size dependence could be parameterized as a function of only AMS based organic and inorganic mass fractions (&lt;i&gt;f&lt;/i&gt;&lt;sub&gt;org&lt;/sub&gt;, &lt;i&gt;f&lt;/i&gt;&lt;sub&gt;inorg&lt;/sub&gt;) using the simple mixing rule &amp;kappa;&lt;sub&gt;p&lt;/sub&gt; ≈ 0.1 · &lt;i&gt;f&lt;/i&gt;&lt;sub&gt;org&lt;/sub&gt; + 0.7 · &lt;i&gt;f&lt;/i&gt;&lt;sub&gt;inorg&lt;/sub&gt;. &lt;br&gt;&lt;br&gt; When the measured air masses originated from the north and passed rapidly over the center of Beijing (fresh city pollution), the average particle hygroscopicity was reduced (&amp;kappa; = 0.2 ± 0.1), which is consistent with enhanced mass fractions of organic compounds (~50%) and EC (~30%) in the fine particulate matter (PM&lt;sub&gt;1&lt;/sub&gt;). Moreover, substantial fractions of externally mixed weakly CCN-active particles were observed at low supersaturation (&lt;i&gt;S&lt;/i&gt;=0.07%), which can be explained by the presence of freshly emitted soot particles with very low hygroscopicity (&amp;kappa; &lt; 0.1). Particles in stagnant air from the industrialized region south of Beijing (aged regional pollution) were on average larger and more hygroscopic, which is consistent with enhanced mass fractions (~60%) of soluble inorganic ions (mostly sulfate, ammonium, and nitrate). Accordingly, the number concentration of CCN in aged air from the megacity region was higher than in fresh city outflow ((2.5–9.9) × 10&lt;sup&gt;3&lt;/sup&gt; cm&lt;sup&gt;−3&lt;/sup&gt; vs. (0.4–8.3) × 10&lt;sup&gt;3&lt;/sup&gt; cm&lt;sup&gt;−3&lt;/sup&gt; for &lt;i&gt;S&lt;/i&gt;=0.07–0.86%) although the total aerosol particle number concentration was lower (1.2 × 10&lt;sup&gt;4&lt;/sup&gt; cm&lt;sup&gt;−3&lt;/sup&gt; vs. 2.3 × 10&lt;sup&gt;4&lt;/sup&gt; cm&lt;sup&gt;−3&lt;/sup&gt;). A comparison with related studies suggests that the fresh outflow from Chinese urban centers generally may contain more, but smaller and less hygroscopic aerosol particles and thus fewer CCN than the aged outflow from megacity regions

A produção científica brasileira sobre as práticas de formação inicial e continuada de professores para educação infantil no período de 1996 a 2006

O presente texto versa sobre pesquisa realizada entre agosto/2006 e novembro/2007 pelos alunos matriculados na disciplina “Praticas de formação do profissional de educação infantil” do Programa de Pós-graduação em Educação da FCT/UNESP. Trata-se de estado da arte da pesquisa sobre práticas de formação inicial e continuada em serviço de professores para educação infantil no Brasil a partir da Lei de Diretrizes e Bases (LDB) 9.394/96 até 2006. O objetivo geral eleito foi dar visibilidade à produção brasileira sobre formação do professor de crianças pequenas e, sobretudo, analisar quais aspectos as pesquisas têm enfatizado relativamente a formação de professores. Assim, os objetivos específicos foram analisar as seguintes categorias: aspectos da formação docente e práticas formativas; papel do professor da educação infantil; aspectos, saberes e experiências necessários ao professor de crianças pequenas; a concepção de criança; função/finalidade social da educação infantil; concepção de educação infantil. A metodologia consistiu em mapeamento bibliográfico e seleção de trabalhos apresentados durante as reuniões da ANPED1 e trabalhos publicados em periódicos nacionais e internacionais na área de educação (Qualis A). A etapa de leituras e análises resultou na seleção de 17 trabalhos e na elaboração das 6 categorias de análise citadas. É possível apontar que o número de pesquisas no período (17) revela que a LDB/96 não impulsionou, como pressupúnhamos, as pesquisas relacionadas às práticas de formação do professor de crianças pequenas. Contudo, influenciou de modo particular os autores das pesquisas a respeito da visão de criança e da função da educação infantil. - This text refers to a research made by students enrolled at the “Childhood Education Professional Formation Practices” from FCT-UNESP Education Post-Graduation Program from August 2006 to November 2007. This research is a state of the art about the initial formation and in service continued education of childhood teachers in Brazil according to Lei de Diretrizes e Bases 9.394/96 (Brazilian Educational Laws and Guidelines – LDB- 9.394/96) 2006. The main objective was emphasizing the Brazilian production related to the childhood teachers training, moreover analyzing which aspects have been considered relevant to teachers’ training. Thus, the specific objectives were analyzing the following categories: teacher’s training aspects and practices; childhood teacher role; knowledge and experiences necessary to the childhood teacher; the teacher’s concept of child; social role/objective of childhood education; concept of childhood education. The methodology was consisted of bibliographical mapping and selection of projects presented at ANPED2 meetings and also of papers published in national and international education journals (Qualis A). Reading and analysis resulted in the selection of 17 projects and in the elaboration of the 06 categories mentioned above. It is safe to say the number of researches in the period (17) reveals that the LDB/96 did not boost, as it was thought, the research related to the childhood teacher training practices. On the other hand, the authors of researches related to the view of child and to the childhood education role were specially influenced

Retrieval of aerosol optical depth over the Arctic cryosphere during spring and summer using satellite observations

The climate in the Arctic has warmed much more quickly in the last 2 to 3 decades than at the mid-latitudes, i.e., during the Arctic amplification (AA) period. Radiative forcing in the Arctic is influenced both directly and indirectly by aerosols. However, their observation from ground or airborne instruments is challenging, and thus measurements are sparse. In this study, total aerosol optical depth (AOD) is determined from top-of-atmosphere reflectance measurements by the Advanced Along-Track Scanning Radiometer (AATSR) on board ENVISAT over snow and ice in the Arctic using a retrieval called AEROSNOW for the period 2003 to 2011. AEROSNOW incorporates an existing aerosol retrieval algorithm with a cloud-masking algorithm, alongside a novel quality-flagging methodology specifically designed for implementation in the high Arctic region (≥ 72∘ N). We use the dual-viewing capability of the AATSR instrument to accurately determine the contribution of aerosol to the reflection at the top of the atmosphere for observations over the bright surfaces of the cryosphere in the Arctic. The AOD is retrieved assuming that the surface reflectance observed by the satellite can be well parameterized by a bidirectional snow reflectance distribution function (BRDF). The spatial distribution of AOD shows that high values in spring (March, April, May) and lower values in summer (June, July, August) are observed. The AEROSNOW AOD values are consistent with those from collocated Aerosol Robotic Network (AERONET) measurements, with no systematic bias found as a function of time. The AEROSNOW AOD in the high Arctic was validated by comparison with ground-based measurements at the PEARL, OPAL, Hornsund, and Thule stations. The AEROSNOW AOD value is less than 0.15 on average, and the linear regression of AEROSNOW and AERONET total AOD yields a slope of 0.98, a Pearson correlation coefficient of R=0.86, and a root mean square error (RMSE) of =0.01 for the monthly scale in both spring and summer. The AEROSNOW observation of increased AOD values over the high Arctic cryosphere during spring confirms clearly that Arctic haze events were well captured by this dataset. In addition, the AEROSNOW AOD results provide a novel and unique total AOD data product for the springtime and summertime from 2003 to 2011. These AOD values, retrieved from spaceborne observation, provide a unique insight into the high Arctic cryospheric region at high spatial resolution and temporal coverage.</p

On distinguishing the natural and human-induced sources of airborne pathogenic viable bioaerosols: characteristic assessment using advanced molecular analysis

Ambient air consists of bioaerosols that constitute many microbes from biosphere due to natural and anthropogenic activities. Size-dependent ambient measurements of bioaerosols at two seminatural and three anthropogenic coastal sites in southern tropical India were taken during the summer 2017. All the five sites considered in this study considerably contributed to the bioaerosol burden with larger contribution from the dumping yard site followed by the marshland site, wastewater treatment plant, composting site, and Indian Institute of Technology Madras. The colony-forming units concentration for all the sites ranged from 17 to 2750 m−3 for bacteria and 42–2673 m−3 for fungi. Firmicutes and Actinomycetes were the dominant phyla observed in 698 bacterial OTUs obtained, and Ascomycota and Zygomycota were the dominant phyla observed in 159 fungal OTUs obtained in the study. Further, the study revealed the presence of pathogenic and ice-nucleating bacteria and fungi in the bioaerosols that can largely affect the well-being of the human population and vegetation in this region. Moreover, the statistical analysis revealed high bacterial abundance and diversity at the grit chamber of wastewater treatment plant and high fungal abundance and diversity at the dumping yard. Further, principal coordinate analysis of the sites studied inferred that the marshland, wastewater treatment plant, and the dumping yard sites shared similar microbial community composition indicating the existence of similar source materials and activities at the sites. Further, this study evidently brings out the fact that urban locations may play an important role in anthropogenic contribution of both pathogenic and ice-nucleating microorganisms. © 2020, Springer Nature Switzerland AG

Size-resolved measurement of the mixing state of soot in the megacity Beijing, China: diurnal cycle, aging and parameterization

Soot particles are the most efficient light absorbing aerosol species in the atmosphere, playing an important role as a driver of global warming. Their climate effects strongly depend on their mixing state, which significantly changes their light absorbing capability and cloud condensation nuclei (CCN) activity. Therefore, knowledge about the mixing state of soot and its aging mechanism becomes an important topic in the atmospheric sciences. &lt;br&gt;&lt;br&gt; The size-resolved (30–320 nm diameter) mixing state of soot particles in polluted megacity air was measured at a suburban site (Yufa) during the CAREBeijing 2006 campaign in Beijing, using a volatility tandem differential mobility analyzer (VTDMA). Particles in this size range with non-volatile residuals at 300 &amp;deg;C were considered to be soot particles. On average, the number fraction of internally mixed soot in total soot particles (&lt;i&gt;F&lt;/i&gt;&lt;sub&gt;in&lt;/sub&gt;), decreased from 0.80 to 0.57 when initial &lt;i&gt;D&lt;/i&gt;&lt;sub&gt;p&lt;/sub&gt; increased from 30 to 320 nm. Further analysis reveals that: (1) &lt;i&gt;F&lt;/i&gt;&lt;sub&gt;in&lt;/sub&gt; was well correlated with the aerosol hygroscopic mixing state measured by a CCN counter. More externally mixed soot particles were observed when particles showed more heterogeneous features with regard to hygroscopicity. (2) &lt;i&gt;F&lt;/i&gt;&lt;sub&gt;in&lt;/sub&gt; had pronounced diurnal cycles. For particles in the accumulation mode (&lt;i&gt;D&lt;/i&gt;&lt;sub&gt;p&lt;/sub&gt; at 100–320 nm), largest &lt;i&gt;F&lt;/i&gt;&lt;sub&gt;in&lt;/sub&gt; were observed at noon time, with "apparent" turnover rates (&lt;i&gt;k&lt;/i&gt;&lt;sub&gt;ex &amp;rarr; in&lt;/sub&gt;) up to 7.8% h&lt;sup&gt;−1&lt;/sup&gt;. (3) &lt;i&gt;F&lt;/i&gt;&lt;sub&gt;in&lt;/sub&gt; was subject to competing effects of both aging and emissions. While aging increases &lt;i&gt;F&lt;/i&gt;&lt;sub&gt;in&lt;/sub&gt; by converting externally mixed soot particles into internally mixed ones, emissions tend to reduce &lt;i&gt;F&lt;/i&gt;&lt;sub&gt;in&lt;/sub&gt; by emitting more fresh and externally mixed soot particles. Similar competing effects were also found with air mass age indicators. (4) Under the estimated emission intensities, actual turnover rates of soot (&lt;i&gt;k&lt;/i&gt;&lt;sub&gt;ex &amp;rarr; in&lt;/sub&gt;) up to 20% h&lt;sup&gt;−1&lt;/sup&gt; were derived, which showed a pronounced diurnal cycle peaking around noon time. This result confirms that (soot) particles are undergoing fast aging/coating with the existing high levels of condensable vapors in the megacity Beijing. (5) Diurnal cycles of &lt;i&gt;F&lt;/i&gt;&lt;sub&gt;in&lt;/sub&gt; were different between Aitken and accumulation mode particles, which could be explained by the faster growth of smaller Aitken mode particles into larger size bins. &lt;br&gt;&lt;br&gt; To improve the &lt;i&gt;F&lt;/i&gt;&lt;sub&gt;in&lt;/sub&gt; prediction in regional/global models, we suggest parameterizing &lt;i&gt;F&lt;/i&gt;&lt;sub&gt;in&lt;/sub&gt; by an air mass aging indicator, i.e., &lt;i&gt;F&lt;/i&gt;&lt;sub&gt;in&lt;/sub&gt; = &lt;i&gt;a&lt;/i&gt; + &lt;i&gt;bx&lt;/i&gt;, where &lt;i&gt;a&lt;/i&gt; and &lt;i&gt;b&lt;/i&gt; are empirical coefficients determined from observations, and &lt;i&gt;x&lt;/i&gt; is the value of an air mass age indicator. At the Yufa site in the North China Plain, fitted coefficients (&lt;i&gt;a&lt;/i&gt;, &lt;i&gt;b&lt;/i&gt;) were determined as (0.57, 0.21), (0.47, 0.21), and (0.52, 0.0088) for &lt;i&gt;x&lt;/i&gt; (indicators) as [NO&lt;sub&gt;z&lt;/sub&gt;]/[NO&lt;sub&gt;y&lt;/sub&gt;], [E]/[X] ([ethylbenzene]/[m,p-xylene]) and ([IM] + [OM])/[EC] ([inorganic + organic matter]/[elemental carbon]), respectively. Such a parameterization consumes little additional computing time, but yields a more realistic description of &lt;i&gt;F&lt;/i&gt;&lt;sub&gt;in&lt;/sub&gt; compared with the simple treatment of soot mixing state in regional/global models

Rapid growth and high cloud-forming potential of anthropogenic sulfate aerosol in a thermal power plant plume during COVID lockdown in India

The COVID lockdown presented an interesting opportunity to study the anthropogenic emissions from different sectors under relatively cleaner conditions in India. The complex interplays of power production, industry, and transport could be dissected due to the significantly reduced influence of the latter two emission sources. Here, based on measurements of cloud condensation nuclei (CCN) activity and chemical composition of atmospheric aerosols during the lockdown, we report an episodic event resulting from distinct meteorological conditions. This event was marked by rapid growth and high hygroscopicity of new aerosol particles formed in the SO2 plume from a large coal-fired power plant in Southern India. These sulfate-rich particles had high CCN activity and number concentration, indicating high cloud-forming potential. Examining the sensitivity of CCN properties under relatively clean conditions provides important new clues to delineate the contributions of different anthropogenic emission sectors and further to understand their perturbations of past and future climate forcing