CCN Properties of Organic Aerosol Collected Below and within Marine Stratocumulus Clouds near Monterey, California

The composition of aerosol from cloud droplets differs from that below cloud. Its implications for the Cloud Condensation Nuclei (CCN) activity are the focus of this study. Water-soluble organic matter from below cloud, and cloud droplet residuals off the coast of Monterey, California were collected; offline chemical composition, CCN activity and surface tension measurements coupled with Köhler Theory Analysis are used to infer the molar volume and surfactant characteristics of organics in both samples. Based on the surface tension depression of the samples, it is unlikely that the aerosol contains strong surfactants. The activation kinetics for all samples examined are consistent with rapid (NH4)2SO4 calibration aerosol. This is consistent with our current understanding of droplet kinetics for ambient CCN. However, the carbonaceous material in cloud drop residuals is far more hygroscopic than in sub-cloud aerosol, suggestive of the impact of cloud chemistry on the hygroscopic properties of organic matter

Catalyzed Gasoline Particulate Filters Reduce Secondary Organic Aerosol Production from Gasoline Direct Injection Vehicles

The effects of photochemical aging on exhaust emissions from two light-duty vehicles with gasoline direct injection (GDI) engines equipped with and without catalyzed gasoline particle filters (GPFs) were investigated using a mobile environmental chamber. Both vehicles with and without the GPFs were exercised over the LA92 drive cycle using a chassis dynamometer. Diluted exhaust emissions from the entire LA92 cycle were introduced to the mobile chamber and subsequently photochemically reacted. It was found that the addition of catalyzed GPFs will significantly reduce tailpipe particulate emissions and also provide benefits in gaseous emissions, including nonmethane hydrocarbons (NMHC). Tailpipe emissions composition showed important changes with the use of GPFs by practically eliminating black carbon and increasing the fractional contribution of organic mass. Production of secondary organic aerosol (SOA) was reduced with GPF addition, but was also dependent on engine design which determined the amount of SOA precursors at the tailpipe. Our findings indicate that SOA production from GDI vehicles will be reduced with the application of catalyzed GPFs through the mitigation of reactive hydrocarbon precursors

Adhesion of Dust Particles to Common Indoor Surfaces in an Air-Conditioned Environment

Adhesion between dust particles and indoor surfaces can lead to negative effects on human health by triggering allergic and asthmatic reactions. In this study, adhesion forces of indoor office dust and activated carbon (AC, as model soot) particles to four common indoor materials (Al, Cu, PVC, and glass) were measured by colloidal probe atomic force microscopy. Chemical analysis of office dust shows it is largely made up of oxygenated hydrophilic organic carbon material. Both metal surfaces experienced weaker dust and AC adhesion than PVC or glass by up to 2–12 times lower primarily due to the presence of attractive electrostatic forces in the latter two (non-conducting) surfaces. Dust and AC adhesion were also highly sensitive to surface roughness, with an inverse relationship between adhesion force and roughness due to the reduction in contact area between the particle and a rougher material surface. Capillary forces play only a minor or negligible role in dust and AC surface adhesion. Adhesion models utilizing a purely van der Waals approach such as the simple Hamaker model and modified Rumpf’s model are insufficient to determine the actual particlesurface contact radii and requires the accounting of non-van der Waals forces to adhesion

Reactivity of aminophenols in forming nitrogen-containing brown carbon from iron-catalyzed reactions

Nitrogen-containing organic carbon (NOC) in atmospheric particles is an important class of brown carbon (BrC). Redox active NOC like aminophenols received little attention in their ability to form BrC. Here we show that iron can catalyze dark oxidative oligomerization of o- and p-aminophenols under simulated aerosol and cloud conditions (pH 1–7, and ionic strength 0.01–1 M). Homogeneous aqueous phase reactions were conducted using soluble Fe(III), where particle growth/agglomeration were monitored using dynamic light scattering. Mass yield experiments of insoluble soot-like dark brown to black particles were as high as 40%. Hygroscopicity growth factors (κ) of these insoluble products under sub- and super-saturated conditions ranged from 0.4–0.6, higher than that of levoglucosan, a prominent proxy for biomass burning organic aerosol (BBOA). Soluble products analyzed using chromatography and mass spectrometry revealed the formation of ring coupling products of o- and p-aminophenols and their primary oxidation products. Heterogeneous reactions of aminophenol were also conducted using Arizona Test Dust (AZTD) under simulated aging conditions, and showed clear changes to optical properties, morphology, mixing state, and chemical composition. These results highlight the important role of iron redox chemistry in BrC formation under atmospherically relevant conditions

Characterizing water-soluble organic aerosol and their effects on cloud droplet formation: Interactions of carbonaceous matter with water vapor

Aerosols have significant impacts on earth's climate and hydrological cycle. They can directly reflect the amount of incoming solar radiation into space; by acting as cloud condensation nuclei (CCN), they can indirectly impact climate by affecting cloud albedo. Our current assessment of the interactions of aerosols and clouds is uncertain and parameters used to estimate cloud droplet formation in global climate models are not well constrained. Organic aerosols attribute much of the uncertainty in these estimates and are known to affect the ability of aerosol to form cloud droplets (CCN Activity) by i) providing solute, thus reducing the equilibrium water vapor pressure of the droplet and ii) acting as surfactants capable of depressing surface tension, and potentially, growth kinetics. My thesis dissertation investigates various organic aerosol species (e.g., marine, urban, biomass burning, Humic-like Substances). An emphasis is placed on the water soluble components and secondary organic aerosols (SOA). In addition the sampled organic aerosols are acquired via different media; directly from in-situ ambient studies (TEXAQS 2006) environmental chamber experiments, regenerated from filters, and cloud water samples. Novel experimental methods and analyses to determine surface tension, molar volumes, and droplet growth rates are presented from nominal volumes of sample. These key parameters for cloud droplet formation incorporated into climate models will constrain aerosol-cloud interactions and provide a more accurate assessment for climate prediction.Ph.D.Committee Chair: Athanasios Nenes; Committee Member: Amyn Teja; Committee Member: Carson Merideth; Committee Member: Michael Bergin; Committee Member: Rodney Webe

The effect of solute dissolution kinetics on cloud droplet formation

This study focuses on the importance of solute dissolution kinetics for cloud droplet formation. To comprehensively account for the kinetics, a numerical model of the process was developed. Simulations of cloud droplet growth were performed for solute diffusivity, droplet growth rates, dry particle and droplet diameters relevant for ambient conditions. Simulations suggest that high ambient supersaturations and a decrease in solute diffusivity are major contributors to significant decreases in effective solute surface concentrations. The numerical simulations were incorporated into Khler theory to assess the impact of dissolution kinetics on the droplet equilibrium vapor pressure. For CCN composed of partially soluble material, a significant increase was found in the equilibrium supersaturation of CCN.M.S.Committee Chair: Dr. Athanasios Nenes; Committee Member: Dr. Amyn Teja; Committee Member: Dr. Rodney Webe

Cloud Forming Potential of Aerosol from Light-duty Gasoline Direct Injection Vehicles

In this study, the authors evaluate the hygroscopicity and droplet kinetics of fresh and aged emissions from new generation gasoline direct injector engines retrofitted with a gasoline particulate filter (GPF). Furthermore, ageing and subsequent secondary aerosol formation is explored in (NH4)2SO4-seeded and non-seeded experiments. The authors explore the impacts on measured and predicted hygroscopicity, CCN-activity, and droplet kinetics of secondary aerosol mixed with initially insoluble carbonaceous materials versus very soluble (NH4)2SO4 seed. The chemical composition and density of the secondary aerosol (SA) formed from aging is measured with an HR-TOF-AMS and a custom-built APM-SMPS system. The supersaturated and subsaturated hygroscopicity of the fresh and aged emission is measured with a DMT Streamwise Thermal Gradient CCN counter and a hygroscopicity tandem differential mobility analyzer (HTDMA), respectively. The measurements show that the fresh gasoline emissions are only slightly hygroscopic in both supersaturated and subsaturated environments. Photochemical aging and subsequent condensation of the secondary aerosol formed from the co-emitted gas phase precursors increases the hygroscopicity of gasoline emissions. Without the GPF, both subsaturated and supersaturated hygroscopicity. When the engine was retrofitted with the GPF, the secondary aerosol (SA) experiments were seeded with (NH4)2SO4. In these experiments the presence of the condensing SA depresses the hygroscopicity of the salt-secondary aerosol mixture. The hygroscopicity was also depressed in the subsaturated regime with time. These changes in the hygroscopicity with aging were additionally sensitive to aerosol dry size distribution. The authors also used threshold droplet growth analysis (TDGA) to evaluate the effects of the condensing SA on droplet kinetics. These results have important implications for the assessment of cloud-aerosol indirect effects of salt-seeded and black carbonaceous aerosol cores. The authors concluded that in the new generation GDI vehicles the point of aerosol emissions will have significant influence on the impacts of the secondary and primary aerosols on climate.View the NCST Project Webpag

Does chronic nitrogen deposition during biomass growth affect atmospheric emissions from biomass burning?

Chronic nitrogen deposition has measureable impacts on soil and plant health. We investigate burning emissions from biomass grown in areas of high and low NO _x deposition. Gas and aerosol-phase emissions were measured as a function of photochemical aging in an environmental chamber at UC-Riverside. Though aerosol chemical speciation was not available, results indicate a systemic compositional difference between biomass grown in high and low deposition areas. Aerosol emissions from biomass grown in areas of high NO _x deposition exhibit a lower volatility than biomass grown in a low deposition area. Furthermore, fuel elemental analysis, NO _x emission rates, and aerosol particle number distributions differed significantly between the two sites. Despite the limited scale of fuels explored, there is strong evidence that the atmospheric emissions community must pay attention to the regional air quality of biomass fuels growth areas