CCN activity of organic aerosols observed downwind of urban emissions during CARES

Mei, Fan; Setyan, Ari; Zhang, Qi; Wang, J. X.

doi:10.5194/acp-13-12155-2013

Cited by 106 publications

(155 citation statements)

References 76 publications

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“…For the 1 h diel averages, the slope of κ org vs. O : C, derived through a bivariate least squares fit (i.e., orthogonal distance regression), is steeper than that derived from laboratory studies of SOA hygroscopicity, especially during IOP2. This steep slope during IOP2 is consistent with the results from earlier field studies (Mei et al, 2013b), although there is a clear offset between the Figure 9. Hygroscopicity of AMS PMF factors for IOP1 (i.e., wet season) retrieved by multilinear regressions using all data (red square), data from UTC 12:00-24:00 (cyan circle), data from UTC 00:00-12:00 (blue triangle), data under background conditions (red triangle), data under polluted conditions (red diamond), and data with hygroscopicity dispersion σ κ CCN /κ CCN less than 0.6 (black diamond).…”

Section: Hygroscopicity Of Pmf Factors and The Variation Of Organic Hsupporting

confidence: 82%

“…The O : C ratios from Mei et al (2013b) and Lambe et al (2011) were scaled by a factor of 1.27 to account for changes in the method of calculating the O : C ratio (Improved-Ambient, Canagaratna et al, 2015), while all O : C values from this work were calculated using the Improved-Ambient method. This offset between the field studies may be partially due to the different precursors of the SOA for the campaigns, with a higher anthropogenic volatile organic compound fraction expected for CalNex and CARES, which took place near Los Angeles and Sacramento, respectively.…”

Section: Hygroscopicity Of Pmf Factors and The Variation Of Organic Hmentioning

confidence: 99%

“…These studies show that the predicted CCN concentration is often sensitive to κ org , especially for aerosol under background conditions where organics tend to dominate submicron aerosol mass (Liu and Wang, 2010;Mei et al, 2013b). Using a constant κ org may lead to large biases in predicted CCN concentrations and aerosol indirect forcing (Liu and Wang, 2010).…”

Section: Introductionmentioning

confidence: 99%

“…A number of recent studies examined the sensitivity of predicted CCN concentration and cloud droplet number concentration to aerosol properties (e.g., Ervens et al, 2010;Kammermann et al, 2010;McFiggans et al, 2006;Mei et al, 2013b;Reutter et al, 2009;Rissman et al, 2004;Roberts et al, 2002;Wang, 2007;Wang et al, 2008). These studies show that the predicted CCN concentration is often sensitive to κ org , especially for aerosol under background conditions where organics tend to dominate submicron aerosol mass (Liu and Wang, 2010;Mei et al, 2013b).…”

Section: Introductionmentioning

confidence: 99%

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CCN activity and organic hygroscopicity of aerosols downwind of an urban region in central Amazonia: seasonal and diel variations and impact of anthropogenic emissions

et al. 2017

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Abstract. During the Observations and Modeling of the Green Ocean Amazon (GoAmazon2014/5) campaign, sizeresolved cloud condensation nuclei (CCN) spectra were characterized at a research site (T3) 60 km downwind of the city of Manaus, Brazil, in central Amazonia for 1 year (12 March 2014 to 3 March 2015. Particle hygroscopicity (κ CCN ) and mixing state were derived from the size-resolved CCN spectra, and the hygroscopicity of the organic component of the aerosol (κ org ) was then calculated from κ CCN and concurrent chemical composition measurements. The annual average κ CCN increased from 0.13 at 75 nm to 0.17 at 171 nm, and the increase was largely due to an increase in sulfate volume fraction. During both wet and dry seasons, κ CCN , κ org , and particle composition under background conditions exhibited essentially no diel variations. The constant κ org of ∼ 0.15 is consistent with the largely uniform and high O : C value (∼ 0.8), indicating that the aerosols under background conditions are dominated by the aged regional aerosol particles consisting of highly oxygenated organic compounds. For air masses strongly influenced by urban pollution and/or local biomass burning, lower values of κ org and organic O : C atomic ratio were observed during night, due to accumulation of freshly emitted particles, dominated by primary organic aerosol (POA) with low hygroscopicity, within a shallow nocturnal boundary layer. The O : C, κ org , and κ CCN increased from the early morning hours and peaked around noon, driven by the formation and aging of secondary organic aerosol (SOA) and dilution of POA emissions into a deeperPublished by Copernicus Publications on behalf of the European Geosciences Union. 11780 R. Thalman et al.: CCN activity and organic hygroscopicity of aerosols downwind of an urban region boundary layer, while the development of the boundary layer, which leads to mixing with aged particles from the residual layer aloft, likely also contributed to the increases. The hygroscopicities associated with individual organic factors, derived from PMF (positive matrix factorization) analysis of AMS (aerosol mass spectrometry) spectra, were estimated through multivariable linear regression. For the SOA factors, the variation of the κ value with O : C agrees well with the linear relationship reported from earlier laboratory studies of SOA hygroscopicity. On the other hand, the variation in O : C of ambient aerosol organics is largely driven by the variation in the volume fractions of POA and SOA factors, which have very different O : C values. As POA factors have hygroscopicity values well below the linear relationship between SOA hygroscopicity and O : C, mixtures with different POA and SOA fractions exhibit a steeper slope for the increase in κ org with O : C, as observed during this and earlier field studies. This finding helps better understand and reconcile the differences in the relationships between κ org and O : C observed in laboratory and field studies, therefore providing a basis for improved parameterizati...

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Section: Hygroscopicity Of Pmf Factors and The Variation Of Organic Hsupporting

confidence: 82%

Section: Hygroscopicity Of Pmf Factors and The Variation Of Organic Hmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

CCN activity and organic hygroscopicity of aerosols downwind of an urban region in central Amazonia: seasonal and diel variations and impact of anthropogenic emissions

et al. 2017

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“…-O : C, the oxygen-to-carbon ratio, for both the bulk and the surface composition of the SOA; it is well known that particle composition, in particular that of the surface, strongly influences the water uptake ability of the particle and its CCN potential (McFiggans et al, 2006;Dusek et al, 2006;Hatch et al, 2008;Moussa et al, 2009;McIntire et al, 2010;Semeniuk et al, 2007; C. Denjean Lamb Wong et al, 2011;Mei et al, 2013;Rickards et al, 2013). To encompass the difficulty of representing the full molecular composition, the O : C of SOA has been included in global climate models to provide a description of the aerosol aging (Tost and Pringle, 2012).…”

Section: Methodsmentioning

confidence: 99%

Relating hygroscopicity and optical properties to chemical composition and structure of secondary organic aerosol particles generated from the ozonolysis of α-pinene

et al. 2015

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Abstract. Secondary organic aerosol (SOA) were generated from the ozonolysis of α-pinene in the CESAM (French acronym for Experimental Multiphasic Atmospheric Simulation Chamber) simulation chamber. The SOA formation and aging were studied by following their optical, hygroscopic and chemical properties. The optical properties were investigated by determining the particle complex refractive index (CRI). The hygroscopicity was quantified by measuring the effect of relative humidity (RH) on the particle size (size growth factor, GF) and on the scattering coefficient (scattering growth factor, f (RH)). The oxygen to carbon atomic ratios (O : C) of the particle surface and bulk were used as a sensitive parameter to correlate the changes in hygroscopic and optical properties of the SOA composition during their formation and aging in CESAM.The real CRI at 525 nm wavelength decreased from 1.43-1.60 (±0.02) to 1.32-1.38 (±0.02) during the SOA formation. The decrease in the real CRI correlated to the O : C decrease from 0.68 (±0.20) to 0.55 (±0.16). In contrast, the GF remained roughly constant over the reaction time, with values of 1.02-1.07 (±0.02) at 90 % (±4.2 %) RH. Simultaneous measurements of O : C of the particle surface revealed that the SOA was not composed of a homogeneous mixture, but contained less oxidised species at the surface which may limit water absorption. In addition, an apparent change in both mobility diameter and scattering coefficient with increasing RH from 0 to 30 % was observed for SOA after 14 h of reaction. We postulate that this change could be due to a change in the viscosity of the SOA from a predominantly glassy state to a predominantly liquid state.

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RACORO continental boundary layer cloud investigations: 1. Case study development and ensemble large‐scale forcings

et al. 2015

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Observation-based modeling case studies of continental boundary layer clouds have been developed to study cloudy boundary layers, aerosol influences upon them, and their representation in cloud-and global-scale models. Three 60 h case study periods span the temporal evolution of cumulus, stratiform, and drizzling boundary layer cloud systems, representing mixed and transitional states rather than idealized or canonical cases. Based on in situ measurements from the Routine AAF (Atmospheric Radiation Measurement (ARM) Aerial Facility) CLOWD (Clouds with Low Optical Water Depth) Optical Radiative Observations (RACORO) field campaign and remote sensing observations, the cases are designed with a modular configuration to simplify use in large-eddy simulations (LES) and single-column models. Aircraft measurements of aerosol number size distribution are fit to lognormal functions for concise representation in models. Values of the aerosol hygroscopicity parameter, κ, are derived from observations to be~0.10, which are lower than the 0.3 typical over continents and suggestive of a large aerosol organic fraction. Ensemble large-scale forcing data sets are derived from the ARM variational analysis, European Centre for Medium-Range Weather Forecasts, and a multiscale data assimilation system. The forcings are assessed through comparison of measured bulk atmospheric and cloud properties to those computed in "trial" large-eddy simulations, where more efficient run times are enabled through modest reductions in grid resolution and domain size compared to the full-sized LES grid. Simulations capture many of the general features observed, but the state-of-the-art forcings were limited at representing details of cloud onset, and tight gradients and high-resolution transients of importance. Methods for improving the initial conditions and forcings are discussed. The cases developed are available to the general modeling community for studying continental boundary clouds.

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CCN activity of organic aerosols observed downwind of urban emissions during CARES

Cited by 106 publications

References 76 publications

CCN activity and organic hygroscopicity of aerosols downwind of an urban region in central Amazonia: seasonal and diel variations and impact of anthropogenic emissions

CCN activity and organic hygroscopicity of aerosols downwind of an urban region in central Amazonia: seasonal and diel variations and impact of anthropogenic emissions

Relating hygroscopicity and optical properties to chemical composition and structure of secondary organic aerosol particles generated from the ozonolysis of α-pinene

RACORO continental boundary layer cloud investigations: 1. Case study development and ensemble large‐scale forcings

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