Collett Research Group Current Projects
Atmospheric Chemistry/Air Quality Program
Atmospheric Science Department
Colorado State University
Fort Collins, Colorado USA


Investigation of San Joaquin Valley Fog Chemistry and Physics during the California Regional Particulate Air Quality Study (CRPAQS)

Sponsor: San Joaquin Valleywide Air Pollution Study Agency
Project Period:  September 2000 - August 2003

As part of the California Regional Particulate Air Quality Study (CRPAQS), measurements of fog chemistry and physics are planned in the San Joaquin Valley (SJV) of California.  The primary objectives of the proposed fog study are to:
 


The Organic Composition of Fogs and Clouds

Sponsor:  National Science Foundation
Project Period:  August 2002 - July 2006

Studies conducted over the last two decades have clearly demonstrated the important roles clouds and fogs play as processors of inorganic fine aerosol particles, contributing both to production of new particle mass and particle removal.  Despite this progress, little is yet known about interactions of fogs and clouds with carbonaceous aerosol particles and organic trace gases.  While several studies have found high organic solute concentrations in both clouds and fogs, the composition and sources of that organic matter are largely unknown.  Previous investigations have typically identified less than 30% of the dissolved organic content of collected cloud and fog samples.

This project is designed to significantly increase knowledge of the organic composition of clouds and fogs and the efficiency with which clouds and fogs scavenge carbonaceous aerosol particles.  The project includes a laboratory development effort to improve capabilities for measuring concentrations of the diverse organic species suspected to be present in cloud and fog drops and a series of field experiments to collect samples suitable for application of the developed suite of organic analytical techniques.  The field campaigns will be used to collect samples of cloud/fog types that are seasonally important in three distinct environments: winter radiation fogs in the California’s Central Valley, spring stratus clouds intercepting the coastal hills of Southern California, and summer orographic clouds intercepting the western slope of the Rocky Mountains.  The first two campaigns will provide information about the organic composition of fogs and clouds in two different urban environments while the third study will gather information about the composition of clouds at a less impacted continental site.  The goal of the analytical work is to significantly increase the fraction of fog/cloud organic matter that is identified as specific organic compounds or characterized with respect to its molecular weight and chemical properties.  Additional field measurements will reveal the efficiency of carbonaceous aerosol particle scavenging by clouds and fogs and how this efficiency varies with particle source type.

Completion of this project is expected to yield several benefits.  First, a suite of analytical approaches suitable for characterization of organic matter present in clouds and fogs will be developed, documented, and shared with the atmospheric chemistry community.  Second, information will be gained about the total concentrations of organic matter present in three important cloud types/environments while the composition of that organic matter will be much better characterized than previously possible.  Increased information about the composition of organic material present in fog and cloud drops will lend new insight into the ways that clouds and fogs process carbonaceous aerosol particles and organic trace gases.  Third, field measurements of the scavenging efficiency of carbonaceous aerosol particles by radiation fogs and stratus clouds will provide key information for inclusion in air quality models.  These findings will also provide new insight into the potential influence of carbonaceous aerosol particles on earth’s climate through modification of cloud properties (the indirect aerosol climate effect).  Last, the project will produce a number of broader impacts including increasing the participation of women in the male-dominated field of atmospheric science (the project will support training of two female atmospheric scientists -one PhD student and one postdoctoral scientist), advancing discovery and understanding while promoting teaching and learning (project results will be incorporated into educational materials to be shared with students and the community at a range of educational levels), and providing new information helpful to making effective policy decisions in the areas of regional air quality and climate change.
 

Field Investigation of Smoke Plumes: aerosol Characterization and Testing of IMPROVE Assumptions

Sponsor:  National Park Service
Project Period: September 2001 - August 2003

A summer 2002 field study in Yosemite National Park focused on the role of smoke aerosol in regional haze.  Field measurements included a suite of physical and chemical measurements.  These included characterizing the complete aerosol size distribution, size-resolved chemical composition, hygroscopic growth, and optical properties.   Chemical measurements included both time-integrated and semi-continuous measurements.

Review and interpretation of aerosol size distribution and hygroscopicity data is currently underway.  These data will be compared with other project data sets, including aerosol composition measurements and measurements of aerosol optical properties.  A variety of measurements were made during the Yosemite study to examine the ionic composition of regional aerosol.  These include collection of particulate matter with aerodynamic diameter less than 2.5 micrometers (PM2.5) filter samples, size-resolved micro-orifice uniform deposit impactor (MOUDI impactor) samples, and near-real-time analysis by a newly acquired Particle into Liquid System (PILS).  High-volume samples were collected throughout the study for identification of organic species using gas chromatography/mass spectrometry (GC/MS). Weekly study composites have been analyzed to identify smoke markers, including levoglucosan, that can apportion a fraction of the organic carbon (OC) mass to smoke-derived aerosols.  In addition we have identified significant concentrations of several organic compounds that indicate an important contribution to secondary organic aerosols from biogenic sources.  We are also testing measurement of levoglucosan, a wood smoke marker, in some of these samples by a newly developed biosensor technique.  New instruments run in the summer 2002 smoke study included a continuous carbon analyzer and a dual wavelength aethalometer.  Upcoming efforts will focus on relating these data to other Yosemite study data sets and evaluating the ability of the instruments to detect the presence of wood smoke on a near real-time basis.  Collaboration is also ongoing with Dr. Graham Bench of Lawrence Livermore National Laboratory.  Dr. Bench has analyzed the carbon isotope composition of several Yosemite samples in order to evaluate relative contributions from “modern” vs. “fossil” carbon.  This approach, which suggests dominant contributions from biogenic carbon sources, complements the organic speciation work.

IMPROVE Nitrate Study

Sponsor:  National Park Service, Land and Water Fund of the Rockies
Project Period: September 2002 - August 2003

A series of field and laboratory studies was planned for 2003 and 2004 to investigate characteristics of nitrate and other ions in aerosol particles at selected, characteristic IMPROVE sites.  These measurements are designed to address the following issues:

In order to address these questions a series of six one month studies was planned.  The first four studies are being completed as part of our 2002-03 work.  These include studies in Bondville, Illinois (Feb. 2003), San Gorgonio Wilderness Area, California (April and July 2003) and Grand Canyon National Park (May 2003).  Additional studies are planned for November 2003 in Brigantine, New Jersey and February 2004 in Sequoia National Park.  Measurements conducted for these studies include: In addition to these field studies, a series of lab experiments is being conducted at CSU to investigate methods used by IMPROVE for nitrate measurement, including issues related to denuder efficiency and filter extraction.  Specific investigations include:

Chemical Heterogeneity Among Fog Drop Populations and its Influence on Aerosol Processing by Fogs

Sponsor:  National Science Foundation
Project Period:  January 2000 - December 2003

Recent NSF sponsorship supported work leading to an increased understanding of chemical heterogeneity present among cloud and fog drop populations and the effects this heterogeneity exerts on aerosol and trace gas processing by clouds and fogs.  Significant effects on both formation of new aerosol mass (via aqueous sulfur oxidation) and aerosol removal (via direct fog drop deposition and by incorporation of cloud drops into precipitation) have been noted. This grant also supported the design, construction, calibration and field testing of two new cloud/fog samplers designed to provide better resolution of drop composition as a function of drop size.  A 3-stage collector was developed for use in supercooled clouds while a 5-stage collector was developed for use in warm clouds and fogs.  These instruments represent a significant advance over previous collector technology which permitted the simultaneous collection of two drop size fractions.  The performance of the two new collectors was evaluated through a combination of numerical modeling and laboratory calibration.  Both collectors have also been thoroughly tested in the field.

This project will apply the newly developed multi-stage collectors to better characterize (in five drop size fractions rather than just two) chemical heterogeneity present among fog drop populations and its influence on aerosol formation and removal in fogs forming in polluted environments.  Studies of polluted fogs are planned because non-uniform drop chemistry appears to exert the greatest effect on aerosol processing in this environment and because an excellent opportunity exists to interface measurements with the upcoming California Regional PM10/PM2.5 Air Quality Study (CRPAQS).  The new multi-stage collectors will be deployed to measure drop size-resolved fog composition in two major field campaigns: in winter 2000/01 during the CRPAQS winter intensive in California’s San Joaquin Valley and in winter 2001/02 in a study of aerosol processing by fogs in Denver’s Brown Cloud.  Results from both studies will represent a considerable advance in understanding of how fog drop composition varies across the drop size spectrum and the influence of this variation on aerosol formation (via gas uptake and aqueous sulfur oxidation) and removal (via drop deposition).  The CRPAQS study will also provide the first good opportunity to test the ability of size-resolved fog chemistry models to accurately predict the size-dependent chemical composition of fogs.  A new 2-stage stainless steel fog sampler will also be developed and deployed in both field campaigns.  This instrument will provide the first reliable information about the distribution of organic carbon across the drop size spectrum and its influence on the ability of urban fogs to cleanse the atmosphere of organic aerosol particles by scavenging and deposition.

Measurement of Fog/Cloud Chemistry and Gaeous Peroxides at the Pittsburgh PM2.5 Supersite

Sponsor:  U.S. Environmental Protection Agency via sucontract from Carnegie Mellon University
Project Period: July 2000 - June 2003

Colorado State University (CSU) will make two types of measurements at the Pittsburgh Supersite.  CSU, in conjunction with Carnegie Mellon researchers, will make gas phase measurements of hydrogen peroxide and soluble organic peroxides using a continuous monitor based on the method of Lazrus et al. (1986). Expertise and instrumentation for the peroxide measurements will be provided by CSU with day-to-day operation handled by CMU personnel.  Samples of fogs and low clouds will also be collected by CSU during a winter intensive study.  Operation of the cloud sampler will be automated for this study.  Fog/cloud presence will be detected using a Gerber Scientific Particulate Volume Monitor.  Collected fog/cloud samples will be analyzed on-site for pH and sample aliquots will be prepared for later analysis of major ion concentrations at CSU.  A subset of samples will also be aliquotted and stabilized for later analysis at CSU of total organic carbon (TOC), formaldehyde, and trace metal catalysts (Fe and Mn).

Peroxide data will be used by other researchers to examine links between peroxide concentrations and health effects.  Peroxide and cloud/fog data will be examined to elucidate the role of regional fogs and clouds on aerosol production and removal.  Rates and dominant pathways of aqueous phase sulfate production will be determined as will efficiencies of aerosol particle scavenging by clouds and fogs.

On-line determination of organic compounds in atmospheric aerosols by direct impaction capillary electrophoresis

Sponsor:  U.S. Department of Energy via subcontract from Aerosol Dynamics, Inc.
Project Period: August 2002 - April 2003

Capillary electrophoresis (CE) is a recently developed technique that has proven quite useful for analysis of various chemical species, including ions, especially in small sample volumes.  CE has the ability to readily separate the mono- and dicarboxylic acids found in the particle phase.  Elution times for dicarboxcylic acids are a few minutes.  Sample preparation is simple by comparison to gas chromatographic methods that require derivatization to enable the elution of these polar compounds. One disadvantage is that CE is not quite as sensitive as ion chromatography. On the other hand, the necessary injection volume is much smaller, approximately 10 nanoliters.  Thus, if one is able to handle the small injection volumes, very small samples can be analyzed and the absolute amount of material required for analysis is much smaller than with ion chromatography.  Further, analysis by CE can identify many more carboxylic and dicarboxylic acid compounds than can ion chromatography.

In this proposal, we outline an approach for concentrating aerosol samples in a small aqueous volume for the in-situ analysis of particle-bound carboxylic acids. We propose a method based on humidification of the samples with collection by impaction, and on-line analysis by capillary electrophoresis.  This proposal addresses the important need to know the origins, formation processes and atmospheric life cycles of the oxygenated acids found in atmospheric aerosols. Because these compounds tend to be hygroscopic, they may play an important role in visibility and cloud formation. At present there is no automated way to quantitatively measure these compounds in situ, with high time resolution. The proposed instrument will provide a robust, economical means to measure the concentrations of individual carboxylic acids on a routine basis.

Development of an Airborne Cloud Water Sampler

Sponsor:  National Science Foundation
Project Period:  March 2001 - February 2003

The objective of the proposed research is to develop, test and deploy an aircraft based cloudwater collection system.  The design will improve upon previous aircraft-based collectors by offering an automated collection system that is capable of obtaining multiple, well-characterized cloudwater samples for chemical analysis. The system will feature a versatile design that will be applicable to multiple research aircraft.

The initial design of the improved aircraft-based cloudwater collector is currently underway.  After an initial review process, an axial flow cyclone design was chosen to provide efficient separation of cloud drops from the ambient airstream. This design was selected for its ability to process relatively large quantities of air in a compact space. The design consists of a duct with a 6 cm diameter inlet that is exposed to the ambient airstream.  As incoming air encounters eight stationary, curved vanes within the duct, the flow is redirected to produce a rotational flow field about the duct centerline.  Centrifugal force resulting from the rotational flow acts to remove cloud drops to the duct wall, where they accumulate and are removed through an extraction slot located downstream of the vanes.

The work to be completed under this proposal will be to continue the development of the cloudwater collection system.  The system will be taken from the initial design and testing phases to the production of a final optimized design suitable for deployment during future field campaigns. As the design of the cloudwater collector progresses, numerical modeling will be used as an ongoing design and analysis tool. Characterization of the flow in and around the cloudwater collector and cloud drop trajectory simulations will be performed with the Computational Fluid Dynamics (CFD) software package, FLUENT v5.0.  A finalized version of the cloudwater collector that incorporates design modifications resulting from the initial testing phase, including wind tunnel tests, and ongoing numerical fluid flow analysis will be assembled.  An automated sample storage system will also be developed as part of the finalized design.  

The collection system will then be deployed in an upcoming field study as a final design test. Two field programs are being considered for possible participation: the Asian Pacific Regional Aerosol Characterization Experiment (ACE-Asia) study and the Megacity Impact on Regional and Global Environment – Mexico City (MIRAGE – Mexico) study both have substantial cloud/aerosol interaction components that would benefit from the ability to collect well-characterized cloudwater samples.  Chemical analysis of collected cloudwater samples will be used to investigate the effects of cloud processing on aerosol particles and the influence of aerosol physical and chemical properties on cloud formation.  This effort will help satisfy the cloud/aerosol objectives of the ACE – Asia and MIRAGE – Mexico programs and provide data for cloud processing, chemical transport, and radiative transfer models.  MORE INFORMATION


Collett Research Group Recent Projects



Application of a Tracer Technique to Study Sulfur Dioxide Oxidation in Cloud Drops as a Function of Drop Size

Sponsor:  National Science Foundation
Project Period: 12/1997 - 11/2000

Recent cloud chemistry models predict cloud drop composition varies with drop size, a prediction confirmed by experimental measurements. Chemical heterogeneity among cloud drop populations has the potential to significantly influence aqueous phase sulfur oxidation. Drop acidity exerts a strong influence on SO2 oxidation by O3. Both drop acidity and concentrations of Fe(III) and Mn(II) affect the rate of trace metal catalyzed S(IV) autooxidation. Observations of size-dependent cloud drop composition suggest that sulfur oxidation by O3 and oxygen should vary with drop size in many environments, typically favoring faster sulfate production in large drops. Due to the non-linear nature of the oxidation rate laws for these pathways, the average oxidation rate in a chemically heterogeneous cloud drop population can also significantly exceed the rate expected from the average drop composition.

In environments where clouds are at least mildly acidic and H2O2 is present at concentrations comparable to or in excess of SO2, H2O2 tends to be the dominant S(IV) oxidant. Observations indicate that H2O2 concentrations do not vary with drop size. Since the oxidation rate for this pathway does not depend on drop acidity over an atmospherically relevant pH range, sulfate production rates are not expected to vary with drop size when H2O2 is the dominant oxidant.

Quantifying sulfur oxidation rates in ambient clouds has always been an extremely difficult task. Recently developed tracer techniques, which examine changes in the ratio of sulfate to a conservative aerosol tracer (Se, As, or Sb) between pre-cloud aerosol and cloud water, however, have been demonstrated capable of accurately quantifying aqueous phase sulfate production.

This project, conducted jointly by the cloud chemistry teams at Colorado State University and at the State University of New York at Albany/ New York State Department of Health, will test the hypothesis that sulfate production does not vary with drop size when H2O2 is the dominant oxidant, but can vary significantly with drop size when oxidation by O3 or trace metal catalyzed autooxidation are dominant. To this end, the study will apply tracer techniques to measure sulfate production in large and small cloud drops collected using a size-fractionating cloud collector. Measurements of droplet composition and gaseous concentrations of SO2, O3 and H2O2 will also be made to permit prediction of sulfur oxidation rates as a function of drop size for comparison with rates determined by the tracer technique. Two environments (Whiteface Mountain, New York, and Davis, California) have been selected for study to ensure that conditions will be encountered where H2O2 is and is not the dominant oxidant.

The study will confirm whether or not predicted variations in sulfate production rates across the cloud drop size spectrum are borne out in real clouds. This information is critical to assessing the need to track variations in drop composition as a function of drop size in cloud chemistry models in order to accurately represent rates of aqueous phase sulfate production and the addition of sulfate mass to aerosol particles released by evaporating clouds.  MORE INFORMATION
 



Big Bend Regional Aerosol and Visibility Observational (BRAVO) Study

Sponsor:  National Park Service
Conducted jointly with S.M. Kredenweis

This project involves participation in the 1999 Big Bend Regional Aerosol and Visibility Observational (BRAVO) Study. The overall project goal is to examine the chemical composition, degree of internal mixing, and scattering and absorption properties of aerosols at Big Bend National Park during July – October, 1999. Air quality at the Park is believed to respond to transport of aerosols and gases across the U.S.-Mexico border, thus our studies seek to not only characterize the haze present at the site under different meteorological conditions but to also apply methods that can help elucidate the sources of particulate matter. Our measurements include organic and inorganic composition of the fine aerosol, aerosol physical size distributions, and trace species identification that will be used to generate a source apportionment of carbonaceous aerosol at the study site.  MORE INFORMATION
 
 


 

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