Q. Chen

Harvard University, Cambridge, Massachusetts, United States

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Publications (39)147.98 Total impact

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    ABSTRACT: The influence of second-generation products on the particle mass yield of beta-caryophyllene ozonolysis was systematically tested and quantified. The approach was to vary the relative concentrations of first- and second-generation products by adjusting the concentration of ozone while observing changes in particle mass yield. For all wall-loss corrected organic particle mass concentrations M-org of this study (0.5 < M-org < 230 mu g m(-3)), the data show that the particle-phase organic material was composed for the most part of second-generation products. For 0.5 < M-org < 10 mu g m(-3), a range which overlaps with atmospheric concentrations, the particle mass yield was 10 to 20% and was not sensitive to ozone exposure, implying that the constituent molecules were rapidly produced at all investigated ozone exposures. In contrast, for M-org > 10 mu g m(-3) the particle mass yield increased to as high as 70% for the ultimate yield corresponding to the greatest ozone exposures. These differing dependencies on ozone exposure under different regimes of M-org are explained by a combination of the ozonolysis lifetimes of the first-generation products and the volatility distribution of the resulting second-generation products. First-generation products that have short lifetimes produce low-volatility second-generation products whereas first-generation products that have long lifetimes produce high-volatility second-generation products. The ultimate particle mass yield was defined by mass-based stoichiometric yields alpha(i) of alpha(0) = 0.17 +/- 0.05, alpha(1) = 0.11 +/- 0.17, and alpha(2) = 1.03 +/- 0.30 for corresponding saturation concentrations of 1, 10, and 100 mu g m(-3). Terms alpha(0) and alpha(1) had low sensitivity to the investigated range of ozone exposure whereas term alpha(2) increased from 0.32 +/- 0.13 to 1.03 +/- 0.30 as the ozone exposure was increased. These findings potentially allow for simplified yet accurate parameterizations in air quality and climate models that seek to represent the ozonolysis particle mass yields of certain classes of biogenic compounds.
    ATMOSPHERIC CHEMISTRY AND PHYSICS 01/2012; 12(7):3165-3179. · 5.51 Impact Factor
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    ABSTRACT: Chemically-resolved submicron aerosol fluxes over both temperate and tropical forest ecosystems were observed during the BEARPEX-07 (Biosphere Effects on AeRosols and Photochemistry EXperiment, Blodgett Forest, California) and AMAZE-08 (AMazonian Aerosol characteriZation Experiment, Brazil) campaigns using a high resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS). While net deposition of non-refractory submicron aerosol was observed, different organic and inorganic components had fluxes of varying magnitudes and directions. The observation of simultaneous upward and downward fluxes suggests that while competing factors influence aerosol fluxes (deposition of transported/regionally-produced aerosols, thermal gradients shifting phase distribution of semi-volatile components, SOA production), the observed flux is the sum of these components. Using our observations, we can constrain the flux contributions and SOA yields resulting from in-canopy chemistry.
    AGU Fall Meeting Abstracts. 12/2011;
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    ABSTRACT: The detection of primary biological material in submicron aerosol by means of thermal desorption/electron impact ionization aerosol mass spectrometry was investigated. Mass spectra of amino acids, carbohydrates, small peptides, and proteins, all of which are key building blocks of biological particles, were recorded in laboratory experiments. Several characteristic marker fragments were identified. The intensity of the marker signals relative to the total organic mass spectrum allows for an estimation of the content of primary biological material in ambient organic aerosol. The developed method was applied to mass spectra recorded during AMAZE-08, a field campaign conducted in the pristine rainforest of the central Amazon Basin, Brazil, during the wet season of February and March 2008. The low abundance of identified marker fragments places upper limits of 7.5% for amino acids and 5.6% for carbohydrates on the contribution of primary biological aerosol particles (PBAP) to the submicron organic aerosol mass concentration during this time period. Upper limits for the absolute submicron concentrations for both compound classes range from 0.01 to 0.1 μg m-3. Carbohydrates and proteins (composed of amino acids) make up for about two thirds of the dry mass of a biological cell. Thus, our findings suggest an upper limit for the PBAP mass fraction of about 20% to the submicron organic aerosol measured in Amazonia during AMAZE-08.
    ATMOSPHERIC CHEMISTRY AND PHYSICS 11/2011; 11(22):11415-11429. · 5.51 Impact Factor
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    ABSTRACT: The abundance of marker compounds for primary biological particles in submicron aerosol was investigated by means of aerosol mass spectrometry. Mass spectra of amino acids, carbohydrates, small peptides, and proteins, all of which are key building blocks of biological particles, were recorded in laboratory experiments. Several characteristic marker peaks were identified. The identified marker peaks were compared with mass spectra recorded during AMAZE-08, a field campaign conducted in the pristine rainforest of the Central Amazon Basin, Brazil, during the wet season of February and March 2008. The low abundance of identified marker peaks places upper limits of 7.5 % for amino acids and 5.6 % for carbohydrates on the contribution of primary biological aerosol particles (PBAPs) to the submicron organic aerosol mass concentration during this time period. Upper limits for the absolute submicron concentrations for both compound classes range from 0.01 to 0.1 mug m-3. Carbohydrates and protein amino acids make up for about two thirds of the dry mass of a biological cell. Thus, our findings suggest an upper limit for the PBAPs mass fraction of about 20 % to the submicron organic aerosol.
    Atmospheric Chemistry and Physics 01/2011; 11:19143-19178. · 4.88 Impact Factor
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    ABSTRACT: Isoprene is the most abundant non-methane biogenic volatile organic compound (BVOC), but the processes governing secondary organic aerosol (SOA) formation from isoprene oxidation are only beginning to become understood and selective quantification of the atmospheric particulate burden remains difficult. Organic aerosol above a tropical rainforest located in Danum Valley, Borneo, Malaysia, a high isoprene emission region, was studied during Summer 2008 using Aerosol Mass Spectrometry and offline detailed characterisation using comprehensive two dimensional gas chromatography. Observations indicate that a substantial fraction (up to 15% by mass) of atmospheric sub-micron organic aerosol was observed as methylfuran (MF) after thermal desorption. This observation was associated with the simultaneous measurements of established gas-phase isoprene oxidation products methylvinylketone (MVK) and methacrolein (MACR). Observations of MF were also made during experimental chamber oxidation of isoprene. Positive matrix factorisation of the AMS organic mass spectral time series produced a robust factor which accounts for an average of 23% (0.18 μg m−3), reaching as much as 53% (0.50 μg m−3) of the total oraganic loading, identified by (and highly correlated with) a strong MF signal. Assuming that this factor is generally representative of isoprene SOA, isoprene derived aerosol plays a significant role in the region. Comparisons with measurements from other studies suggest this type of isoprene SOA plays a role in other isoprene dominated environments, albeit with varying significance.
    Atmospheric Chemistry and Physics 01/2011; · 4.88 Impact Factor
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    ABSTRACT: The production of secondary organic aerosol (SOA) by the dark ozonolysis of gas-phase beta-caryophyllene was studied. The experiments were conducted in a continuous-flow environmental chamber for organic particle mass concentrations of 0.5 to 30 mu g m(-3) and with ozone in excess, thereby allowing the study of second-generation particle-phase products under atmospherically relevant conditions. The particle-phase products were characterized by an ultra-performance liquid chromatograph equipped with an electrospray ionization time-of-flight mass spectrometer (UPLC-ESI-ToF-MS). Fragmentation mass spectra were used for the structural elucidation of each product, and the structures were confirmed as consistent with the accurate m/z values of the parent ions. In total, fifteen products were identified. Of these, three are reported for the first time. The structures showed that 9 out of 15 particle-phase products were second generation, including all three of the new products. The relative abundance of the second-generation products was approximately 90% by mass among the 15 observed products. The O:C and H:C elemental ratios of the 15 products ranged from 0.13 to 0.50 and from 1.43 to 1.60, respectively. Fourteen of the products contained 3 to 5 oxygen atoms. A singular product, which was one of the three newly identified ones, had 7 oxygen atoms, including 1 carboxylic group, 2 carbonyl groups, and 3 hydroxyl groups. It was identified as 2, 3-dihydroxy-4-[2-(4-hydroxy-3-oxobutyl)3, 3-dimethylcyclobutyl]-4-oxobutanoic acid (C14H22O7). The estimated saturation vapor pressure of this product is 3.3x10(-13) Pa, making this product a candidate contributor to new particle formation in the atmosphere.
    ATMOSPHERIC CHEMISTRY AND PHYSICS 01/2011; · 5.51 Impact Factor
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    ABSTRACT: Isoprene is the dominant biogenic non-methane hydrocarbon in the atmosphere, and an important precursor for secondary organic aerosol (SOA). Isoprene emissions are most prevalent in tropical and subtropical regions. The global emissions of isoprene are in the range of ~600 Tg yr-1 while the resulting SOA mass from isoprene based on chamber studies is estimated to be in the range of ~6-30 Tg yr-1. Recent field studies in tropical regions show that the aerosol is dominated by SOA with mass concentrations exceeding expectations based on yields found in chamber studies, suggesting additional pathways. Batch experiments have shown that aqueous phase chemistry might be an additional pathway for SOA from isoprene oxidation. This study tries to explore the influence of the liquid phase (e.g., humidity and liquid water content) onto the isoprene oxidation by OH as well as on the resulting products that can be found in the particle phase. The platform for these investigations is the Harvard Environmental Chamber (HEC), which can be operated with constant in- and outflow in the so called steady state mode. The investigation of gas and particle phase and isoprene OH oxidation products was performed using state of the art instrumentation such as high resolution time-of-flight aerosol mass spectrometry for aerosol mass and elemental composition and high performance liquid chromatography for molecular identification of known first and second generation products of isoprene, and electrospray ionization time-of-flight mass spectrometry for further reaction products such as tetrols and oligomers. Further possible influences of the liquid phase chemistry onto particle hygroscopicity and cloud condensation nuclei activity are investigated.
    AGU Fall Meeting Abstracts. 12/2010;
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    ABSTRACT: The Amazon is one of the few continental regions where atmospheric aerosol particles and their effects on climate are not dominated by anthropogenic sources. During the wet season, the ambient conditions approach those of the pristine pre-industrial era. We show that the fine submicrometer particles accounting for most cloud condensation nuclei are predominantly composed of secondary organic material formed by oxidation of gaseous biogenic precursors. Supermicrometer particles, which are relevant as ice nuclei, consist mostly of primary biological material directly released from rainforest biota. The Amazon Basin appears to be a biogeochemical reactor, in which the biosphere and atmospheric photochemistry produce nuclei for clouds and precipitation sustaining the hydrological cycle. The prevailing regime of aerosol-cloud interactions in this natural environment is distinctly different from polluted regions.
    Science 09/2010; 329(5998):1513-6. · 31.20 Impact Factor
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    ABSTRACT: The Amazon Basin provides an excellent environment for studying the sources, transformations, and properties of natural aerosol particles and the resulting links between biological processes and climate. With this framework in mind, the Amazonian Aerosol Characterization Experiment (AMAZE-08), carried out from 7 February to 14 March 2008 during the wet season in the central Amazon Basin, sought to understand the formation, transformations, and cloud-forming properties of fine- and coarse-mode biogenic aerosol particles, especially as related to their effects on cloud activation and regional climate. Special foci included (1) the production mechanisms of secondary organic components at a pristine continental site, including the factors regulating their temporal variability, and (2) predicting and understanding the cloud-forming properties of biogenic particles at such a site. In this overview paper, the field site and the instrumentation employed during the campaign are introduced. Observations and findings are reported, including the large-scale context for the campaign, especially as provided by satellite observations. New findings presented include: (i) a particle number-diameter distribution from 10 nm to 10 μm that is representative of the pristine tropical rain forest and recommended for model use; (ii) the absence of substantial quantities of primary biological particles in the submicron mode as evidenced by mass spectral characterization; (iii) the large-scale production of secondary organic material; (iv) insights into the chemical and physical properties of the particles as revealed by thermodenuder-induced changes in the particle number-diameter distributions and mass spectra; and (v) comparisons of ground-based predictions and satellite-based observations of hydrometeor phase in clouds. A main finding of AMAZE-08 is the dominance of secondary organic material as particle components. The results presented here provide mechanistic insight and quantitative parameters that can serve to increase the accuracy of models of the formation, transformations, and cloud-forming properties of biogenic natural aerosol particles, especially as related to their effects on cloud activation and regional climate.
    Atmospheric Chemistry and Physics 07/2010; · 4.88 Impact Factor
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    ABSTRACT: Cloud condensation nuclei in pristine tropical rainforest air of Amazonia: size-resolved measurements and modeling of atmospheric aerosol composition and CCN activity
    ATMOSPHERIC CHEMISTRY AND PHYSICS 04/2010; · 5.51 Impact Factor
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    ABSTRACT: The cloud condensation nuclei (CCN) properties of ammonium sulfate particles mixed with organic material condensed during the hydroxyl-radical-initiated photooxidation of isoprene (C5H8) were investigated in the continuous-flow Harvard Environmental Chamber. CCN activation curves were measured for organic particle mass concentrations of 0.5 to 10.0 μg m−3, NOx concentrations from under 0.4 ppbv up to 38 ppbv, particle mobility diameters from 70 to 150 nm, and thermodenuder temperatures from 25 to 100 °C. At 25 °C, the observed CCN activation curves were accurately described by a Köhler model having two internally mixed components, namely ammonium sulfate and secondary organic material. The modeled physicochemical parameters of the organic material were equivalent to an effective hygroscopicity parameter κORG of 0.10±0.03, regardless of the C5H8:NOx concentration ratio for the span of >200:0.4 to 50:38 (ppbv:ppbv). The volatilization curves (i.e., plots of the residual organic volume fraction against temperature) were also similar for the span of investigated C5H8:NOx ratios, suggesting a broad similarity of particle chemical composition. This suggestion was supported by limited variance at 25 °C among the particle mass spectra. For example, the signal intensity at m/z 44 (which can result from the fragmentation of oxidized molecules believed to affect hygroscopicity and CCN properties) varied weakly from 6 to 9% across the range of investigated conditions. In contradistinction to the results for 25 °C, conditioning up to 100 °C in the thermodenuder significantly reduced CCN activity. The altered CCN activity might be explained by chemical reactions (e.g., decomposition or oligomerization) of the secondary organic material at elevated temperatures. The study's results at 25 °C, in conjunction with the results of other chamber and field studies for a diverse range of conditions, suggest that a value of 0.10±0.05 for κORG is representative of both anthropogenic and biogenic secondary organic material. This finding supports the use of κORG as a simplified yet accurate general parameter to represent the CCN activation of secondary organic material in large-scale atmospheric and climate models.
    ATMOSPHERIC CHEMISTRY AND PHYSICS 01/2010; · 5.51 Impact Factor
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    ABSTRACT: This review provides a comprehensive account of what is known presently about Amazonian aerosol particles and concludes by formulating outlook and priorities for further research. The review is organized to follow the life cycle of Amazonian aerosol particles. It begins with a discussion of the primary and secondary sources relevant to the Amazonian particle burden, followed by a presentation of the particle properties that characterize the mixed populations present over the Amazon Basin at different times and places. These properties include number and mass concentrations and distributions, chemical composition, hygroscopicity, and cloud nucleation ability. The review presents Amazonian aerosol particles in the context of natural compared to anthropogenic sources as well as variability with season and meteorology. This review is intended to facilitate an understanding of the current state of knowledge on Amazonian aerosol particles specifically and tropical continental aerosol particles in general and thereby to enhance future research in this area.
    Reviews of Geophysics 01/2010; · 13.91 Impact Factor
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    ABSTRACT: No abstract available.
    ATMOSPHERIC CHEMISTRY AND PHYSICS 01/2010; · 5.51 Impact Factor
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    ABSTRACT: The production of secondary organic aerosol (SOA) by the dark ozonolysis of gas-phase β-caryophyllene was studied. The experiments were conducted in a continuous-flow environmental chamber for organic particle mass concentrations of 0.5 to 30 μg m<sup>−3</sup> and with ozone in excess, thereby allowing the study of second-generation particle-phase products under atmospherically relevant conditions. The particle-phase products were characterized by an ultra-performance liquid chromatograph equipped with an electrospray ionization time-of-flight mass spectrometer (UPLC-ESI-ToF-MS). Fragmentation mass spectra were used for the structural elucidation of each product, and the structures were confirmed as consistent with the accurate m/z values of the parent ions. In total, fifteen products were identified, three of which are reported for the first time in this study. The structures showed that 9 out of 15 particle-phase products were second generation, including all three of the new products. The relative abundance of the second-generation products was approximately 90% by mass among the 15 observed products. The O:C and H:C elemental ratios of the 15 products ranged from 0.13 to 0.50 and from 1.43 to 1.60, respectively. Fourteen of the products contained 3 to 5 oxygen atoms. A singular product, which was one of the three newly identified ones, had 7 oxygen atoms, including 1 carboxylic group, 2 carbonyl groups, and 3 hydroxyl groups. It was identified as 2,3-dihydroxy-4-[2-(4-hydroxy-3-oxobutyl)-3,3-dimethylcyclobutyl]-4-oxobutanoic acid (C<sub>14</sub>H<sub>22</sub>O<sub>7</sub>). The estimated saturation vapor pressure of this product is sufficiently low (3.3×10<sup>−13</sup> Pa) that it can contribute to new particle formation in the atmosphere.
    Atmospheric Chemistry and Physics 01/2010; · 4.88 Impact Factor
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    ABSTRACT: The influence of drying rate on the dynamic shape factor χ of NaCl particles was investigated. The drying rate at the efflorescence relative humidity (ERH) of 45% was controlled in a laminar flow tube and varied from 5.5 ± 0.9 to 101 ± 3 RH s at ERH, where RH represents one percent unit of relative humidity. Dry particles having mobility diameters of 23–84 nm were studied, corresponding to aqueous particles of 37–129 nm at the RH (57%) prior to drying. At each mobility diameter and drying rate, the critical supersaturation of cloud-condensation activation was also measured. The mobility diameter and the critical supersaturation were combined in an analysis to determine the value of χ. The measured values varied from 1.02 to 1.26. For fixed particle diameter the χ value decreased with increasing drying rate. For fixed drying rate, a maximum occurred in χ between 35- and 40-nm dry mobility diameter, with a lower χ for both smaller and larger particles. The results of this study, in conjunction with the introduced apparatus for obtaining quantified drying rates, can allow the continued development of a more detailed understanding of the morphology of submicron salt particles, with the potential for the follow-on development of quantitative modeling of evaporation and crystal growth at these dimensions.
    Aerosol Science and Technology, v.44, 939-953 (2010). 01/2010;
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    Atmospheric Chemistry and Physics 01/2010; 10:11565. · 4.88 Impact Factor
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    ABSTRACT: The Amazon Basin provides an excellent environment for studying the sources, transformations, and properties of natural aerosol particles and the resulting links between biological processes and climate. With this framework in mind, the Amazonian Aerosol Characterization Experiment (AMAZE-08), carried out from 7 February to 14 March 2008 during the wet season in the central Amazon Basin, sought to understand the formation, transformations, and cloud-forming properties of fine- and coarse-mode biogenic aerosol particles, especially as related to their effects on cloud activation and regional climate. Special foci included (1) the production mechanisms of secondary organic components at a pristine continental site, including the factors regulating their temporal variability, and (2) predicting and understanding the cloud-forming properties of biogenic particles at such a site. In this overview paper, the field site and the instrumentation employed during the campaign are introduced. Observations and findings are reported, including the large-scale context for the campaign, especially as provided by satellite observations. New findings presented include: (i) a particle number-diameter distribution from 10 nm to 10 μm that is representative of the pristine tropical rain forest and recommended for model use; (ii) the absence of substantial quantities of primary biological particles in the submicron mode as evidenced by mass spectral characterization; (iii) the large-scale production of secondary organic material; (iv) insights into the chemical and physical properties of the particles as revealed by thermodenuder-induced changes in the particle number-diameter distributions and mass spectra; and (v) comparisons of ground-based predictions and satellite-based observations of hydrometeor phase in clouds. A main finding of AMAZE-08 is the dominance of secondary organic material as particle components. The results presented here provide mechanistic insight and quantitative parameters that can serve to increase the accuracy of models of the formation, transformations, and cloud-forming properties of biogenic natural aerosol particles, especially as related to their effects on cloud activation and regional climate.
    ATMOSPHERIC CHEMISTRY AND PHYSICS 01/2010; · 5.51 Impact Factor
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    ABSTRACT: Organic aerosol (OA) in the atmosphere consists of a multitude of organic species which are either directly emitted or the products of a variety of chemical reactions. This complexity challenges our ability to explicitly characterize the chemical composition of these particles. We find that the bulk composition of OA from a variety of environments (laboratory and field) occupies a narrow range in the space of a Van Krevelen diagram (H:C versus O:C), characterized by a slope of ˜-1. The data show that atmospheric aging, involving processes such as volatilization, oxidation, mixing of air masses or condensation of further products, is consistent with movement along this line, producing a more oxidized aerosol. This finding has implications for our understanding of the evolution of atmospheric OA and representation of these processes in models.
    Geophysical Research Letters 01/2010; 37(8). · 3.98 Impact Factor
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    ABSTRACT: Statistical algorithms are described for 3-D signal reconstruction problems where the object has a helical symmetry with unknown symmetry parameters and the data is cryo electron micrographs of multiple identical instances of the object. Two object models are described: a Fourier-Bessel series model for a helical object and a spherical harmonics series model for a motif which is then replicated in an array to form a helical object where, in both cases, the unknown parameters are the coefficients in the series. The measured images are essentially noisy 2-D projections of the 3-D electron scattering intensity where the projection orientation is not known. A maximum likelihood estimator computed by an expectation-maximization algorithm is used in both cases to estimate the unknown parameters.
    Biomedical Imaging: From Nano to Macro, 2009. ISBI '09. IEEE International Symposium on; 08/2009
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    ABSTRACT: 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 S=0.10–0.82% in pristine tropical rainforest air during the AMAZE-08 campaign in central Amazonia. The effective hygroscopicity parameters describing the influence of chemical composition on the CCN activity of aerosol particles varied in the range of κ≈0.1–0.4 (0.16±0.06 arithmetic mean and standard deviation). The overall median value of κ≈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 (κ≈0.1 at D≈50 nm; κ≈0.2 at D≈200 nm), which is in agreement with earlier hygroscopicity tandem differential mobility analyzer (H-TDMA) studies. The CCN measurement results are consistent with aerosol mass spectrometry (AMS) data, showing that the organic mass fraction (forg) was on average as high as ~90% in the Aitken mode (D≤100 nm) and decreased with increasing particle diameter in the accumulation mode (~80% at D≈200 nm). The κ values exhibited a negative linear correlation with forg (R2=0.81), and extrapolation yielded the following effective hygroscopicity parameters for organic and inorganic particle components: κorg≈0.1 which can be regarded as the effective hygroscopicity of biogenic secondary organic aerosol (SOA) and κinorg≈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 (κp=κorg×forg +κinorg×finorg). The CCN number concentrations predicted with κp were in fair agreement with the measurement results (~20% average deviation). The median CCN number concentrations at S=0.1–0.82% ranged from NCCN,0.10≈35 cm−3 to NCCN,0.82≈160 cm−3, the median concentration of aerosol particles larger than 30 nm was NCN,30≈200 cm−3, and the corresponding integral CCN efficiencies were in the range of NCCN,0.10/NCN,30≈0.1 to NCCN,0.82/NCN,30≈0.8. 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 NCCN,S assuming an approximate global average value of κ≈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 (≤100 cm−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. 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.
    Atmospheric Chemistry and Physics. 01/2009;