The work in the Cappa group encompasses both laboratory and field studies. Our work is highly collaborative. A brief look at some of the on-going and past projects is provided below. Results from these studies can be found on our publications page.
LABORATORY STUDIES
CAICE – The Center for Aerosol Impacts on Climate and the Environment
The Center for Aerosol Impacts on Climate and the Environment (CAICE) is an NSF-funded Center for Chemical Innovation. In addition to UC Davis, CAICE involves researchers from UC San Diego, Scripps Institution of Oceanography, the University of Iowa, the University of Wisconsin, Madison, the University of Utah, Colorado State University and Yale University. CAICE aims to develop a detailed chemical understanding of the structure, phase and molecular composition of sea spray at the individual particle level to facilitate prediction of how ocean and particle chemistry influence climate-relevant particle properties, such as light absorption and scattering and how they nucleate cloud droplets and ice crystals.
Chemistry and Aerosol Optics
It is well known that the composition of particles is intimately tied to their observed optical properties (i.e. ability to absorb and scatter light). We have been exploring this relationship in detail through laboratory studies, with a particular focus on understanding how chemical complexity of the organic aerosol fraction and heterogeneous reactions affect the aerosol optics. This work has potential implications for understanding how region-to-region variability in organic aerosol emission sources and long-term processing influences the local radiative balance. This work is supported by NSF.
Volatility, Oxidation and Phase of Organic Aerosol
The sensitivity of atmospheric aerosols to changes in temperature can affect the observed abundance of the aerosol by influencing the gas-particle partitioning of semi-volatile compounds. Additionally, measurements of particle volatility can provide information on the chemical nature of the aerosol, especially when coupled with real-time composition measurements. We are working to understand how measurements of temperature-dependent composition can be used to provide quantitative information about the nature of particles sampled in different environments or subject to different levels of chemical processing.
Chemical composition plays an important role in determining the lifetime and climate impacts of atmospheric aerosols. We are working in collaboration with researchers at the Advanced Light Source at Lawrence Berkeley National Laboratory to characterize how heterogeneous oxidation of organic aerosols by OH radicals affects particle composition, volatility, phase, hygroscopicity and optical properties. We use a unique VUV aerosol mass spectrometer (on beamline 9.0.2.) to determine the timescales and aerosol chemical evolution associated with oxidation of organic aerosol. This work is supported by NSF.
Formation and Transformations of Secondary Organic Aerosol
We have developed a new model, termed the Statistical Oxidation Model (SOM) to describe the formation of secondary organic aerosol (SOA) in laboratory chambers and the atmosphere. The SOM is an intermediate complexity model that quantitatively describes the multi-generation oxidation of gas-phase SOA precursors and their dynamic formation of SOA. This model has been used to assess the formation of SOA from various alkanes, and is currently being developed so that it can be used within 3D air quality models. Initial model development was supported by NSF and the application of the SOM within a 3D model is supported by CARB.
Light Absorption by Soot
Soot produced from combustion processes is the dominant source of particles that absorb light in the atmosphere. Soot (or “black carbon” has a complex morphology where a soot particle is generally composed of many small spherules which stick together. As such, prediction of the optical properties of soot from theory are difficult. It is also known that the presence of non-absorbing coatings on light absorbing particle cores can lead to an enhancement of the total light absorption. However, theoretical methods used to calculate this enhancement by necessity use a spherical core-shell model, which is most certainly not the case for soot. We are interested in constraining the theoretical predictions through direct measurement of the light absorption enhancement for soot to determine to what extent the “core-shell” model can be accurately used in global climate models. Towards this goal, we have been collaborating with researchers at Boston College and Aerodyne Research determine quantitative relationships between BC particle optical properties and their coating state and morphology. An overview of the type of measurements we make was published in AS&T.
FIELD CAMPAIGNS
SOAS 2013
The Southern Oxidant and Aerosol Study (SOAS) took place during June/July 2013. SOAS was focused on understanding and characterizing the processes that contribute to the formation of secondary organic aerosol in the southeast US. We deployed our dual-wavelength CRD-PAS instrument at the Look Rock, TN ground site.
DISCOVER-AQ 2013
The NASA DISCOVER-AQ series of studies are focused on improving the use of satellites to monitor air quality for public health and environmental benefit through in situ measurement. We deployed our dual-wavelength CRD-PAS instrument at ground site in Fresno, CA during the California mission during Jan/Feb 2013.
ClearfLo 2012
We are contributing to analysis of optical property measurements made during the 2012 DOE Clear Air for London (ClearfLo) study, which was aimed at understanding and characterizing aerosol sources and processing at a rural site southeast of London, UK.
CARES 2010
The Carbonaceous Aerosols and Radiative Effects Study (CARES) is a DOE sponsored field project that took place during June 2010 in the Sacramento area. There are two ground sites, one at American River College in Sacramento and one in Cool, CA. A G1 aircraft is also being deployed. The Cappa group made measurements of aerosol optical properties at the “T0” site at ARC. Analyses of optical property measurements during CARES is supported by the US DOE.
CalNex 2010
We participated in the 2010 CalNex field campaign during May-June 2010. Measurements of aerosol extinction and absorption were made using our dual wavelength Cavity Ringdown/Photoacoustic Spectrometer (CRD-PAS) on board the Research Vessel Atlantis. A ocus of our analysis has been on how aging and composition of particles modifies their optical properties and on characterization of emissions of black carbon from shipping activities. This work is funded by NOAA and U.S. EPA. Among other results, the observations from CalNex and CARES have led to new understanding of how black carbon particles in the atmosphere absorb sunlight.
ICEALOT 2008
During March and April of 2008 a research cruise to the Arctic, the “International Chemistry Experiment in the Arctic LOwer Troposphere,” or ICEALOT) was undertaken in order to characterize the levels and nature of the particles that make up the “Arctic Haze.” As part of ICEALOT we made direct measurements of the light absorption and extinction by the Arctic aerosol using photoacoustic spectroscopy and cavity ringdown spectroscopy, respectively. Analysis of the data is ongoing. This work is supported by NOAA. The Arctic is known to be more sensitive to climate change than the rest of the world, with Arctic temperatures rising at about 2x the global average. Recent years have seen a significant decline in the abundance of Arctic sea-ice. Besides the influence of greenhouse gases, particles in the atmosphere that absorb solar radiation (e.g. soot) can have a strong warming effect on the climate. Soot plays an additional role in the Arctic through deposition on white snow and ice, effectively decreasing the reflectivity of the snow and ice – this leads to greater light absorption at the surface and increased melting of the ice. As sea-ice melts, darker ocean water is exposed to direct sunlight which causes the region to absorb even more solar radiation and to warm even faster (this is called a positive feedback and usually referred to as the ice-albedo feedback.)
LABORATORY STUDIES
CAICE – The Center for Aerosol Impacts on Climate and the Environment
The Center for Aerosol Impacts on Climate and the Environment (CAICE) is an NSF-funded Center for Chemical Innovation. In addition to UC Davis, CAICE involves researchers from UC San Diego, Scripps Institution of Oceanography, the University of Iowa, the University of Wisconsin, Madison, the University of Utah, Colorado State University and Yale University. CAICE aims to develop a detailed chemical understanding of the structure, phase and molecular composition of sea spray at the individual particle level to facilitate prediction of how ocean and particle chemistry influence climate-relevant particle properties, such as light absorption and scattering and how they nucleate cloud droplets and ice crystals.
Chemistry and Aerosol Optics
It is well known that the composition of particles is intimately tied to their observed optical properties (i.e. ability to absorb and scatter light). We have been exploring this relationship in detail through laboratory studies, with a particular focus on understanding how chemical complexity of the organic aerosol fraction and heterogeneous reactions affect the aerosol optics. This work has potential implications for understanding how region-to-region variability in organic aerosol emission sources and long-term processing influences the local radiative balance. This work is supported by NSF.
Volatility, Oxidation and Phase of Organic Aerosol
The sensitivity of atmospheric aerosols to changes in temperature can affect the observed abundance of the aerosol by influencing the gas-particle partitioning of semi-volatile compounds. Additionally, measurements of particle volatility can provide information on the chemical nature of the aerosol, especially when coupled with real-time composition measurements. We are working to understand how measurements of temperature-dependent composition can be used to provide quantitative information about the nature of particles sampled in different environments or subject to different levels of chemical processing.
Chemical composition plays an important role in determining the lifetime and climate impacts of atmospheric aerosols. We are working in collaboration with researchers at the Advanced Light Source at Lawrence Berkeley National Laboratory to characterize how heterogeneous oxidation of organic aerosols by OH radicals affects particle composition, volatility, phase, hygroscopicity and optical properties. We use a unique VUV aerosol mass spectrometer (on beamline 9.0.2.) to determine the timescales and aerosol chemical evolution associated with oxidation of organic aerosol. This work is supported by NSF.
Formation and Transformations of Secondary Organic Aerosol
We have developed a new model, termed the Statistical Oxidation Model (SOM) to describe the formation of secondary organic aerosol (SOA) in laboratory chambers and the atmosphere. The SOM is an intermediate complexity model that quantitatively describes the multi-generation oxidation of gas-phase SOA precursors and their dynamic formation of SOA. This model has been used to assess the formation of SOA from various alkanes, and is currently being developed so that it can be used within 3D air quality models. Initial model development was supported by NSF and the application of the SOM within a 3D model is supported by CARB.
Light Absorption by Soot
Soot produced from combustion processes is the dominant source of particles that absorb light in the atmosphere. Soot (or “black carbon” has a complex morphology where a soot particle is generally composed of many small spherules which stick together. As such, prediction of the optical properties of soot from theory are difficult. It is also known that the presence of non-absorbing coatings on light absorbing particle cores can lead to an enhancement of the total light absorption. However, theoretical methods used to calculate this enhancement by necessity use a spherical core-shell model, which is most certainly not the case for soot. We are interested in constraining the theoretical predictions through direct measurement of the light absorption enhancement for soot to determine to what extent the “core-shell” model can be accurately used in global climate models. Towards this goal, we have been collaborating with researchers at Boston College and Aerodyne Research determine quantitative relationships between BC particle optical properties and their coating state and morphology. An overview of the type of measurements we make was published in AS&T.