Grantee Research Project Results
1998 Progress Report: Real-Time Monitoring of Individual Atmospheric Aerosol Particles: Establishing Correlations Between Particle Size and Chemical Speciation
EPA Grant Number: R826240Title: Real-Time Monitoring of Individual Atmospheric Aerosol Particles: Establishing Correlations Between Particle Size and Chemical Speciation
Investigators: Prather, Kimberly A.
Institution: University of California - Riverside
EPA Project Officer: Hahn, Intaek
Project Period: February 1, 1998 through January 31, 2001
Project Period Covered by this Report: February 1, 1998 through January 31, 1999
Project Amount: $547,000
RFA: Ambient Air Quality (1997) RFA Text | Recipients Lists
Research Category: Air Quality and Air Toxics , Air
Objective:
The objectives of this research project involve using a newly developed aerosol analysis technique developed in our laboratory, aerosol time-of-flight mass spectrometry (ATOFMS), for taking real-time measurements of the individual particle size and composition of ambient aerosols in a variety of locations in the United States. ATOFMS couples time-of-flight aerodynamic sizing with laser desorption ionization (LDI) time-of-flight mass spectrometry, simultaneously measuring the size and chemical composition (as anions and cations) of individual aerosol particles in real time. One major objective involves measuring size-resolved chemical composition at the single-particle level at locations with unique air mass characteristics. Single-particle signatures in mass spectra will be used to explore particle changes due to aging/chemistry as well as to obtain information on particle sources in different regions of the United States. These studies will represent the first long-term studies performed using ATOFMS. Therefore, efforts will be made to convert the qualitative data into more semiquantitative information on atmospheric particles that can be compared with other gas phase, particle phase, and meteorological data in an effort to further our understanding of aerosol chemistry on shorter timescales.
Progress Summary:
During the first year of this research project, two field studies were conducted with the transportable ATOFMS, the Grand Canyon Visibility Study (June 21, 1998-July 12, 1998) and the Scripps Pier Study in San Diego, CA, between December 14-15, 1998. The Grand Canyon study involved examining the single-particle types present in this region. The motivation behind the study was to provide insight into the chemical composition of particles present during times of reduced visibility. An inability to apportion 50 percent of extinction budget in Grand Canyon was noted. Part of this lack of understanding stems from the fact that researchers using traditional sampling and analysis methods can only treat particle composition as an internal mixture (i.e., assume all particles in a given size range have identical compositions). In the case of the Grand Canyon, this mixture, in the fine-size range (< 2.5 µm), contained five different particle types: sulfates, nitrates, organics, light-absorbing carbon, and soil.
Our objective during this study was to shed light on the chemical associations between these species because it is these couplings that will control the ability of the particles to scatter and/or absorb light (i.e., sulfates on salt versus sulfates on electrical conductivity will have very different extinction properties). Furthermore, we hoped to shed some light on the sources of the particles (i.e., vehicles, biomass) as well as their origin (i.e., Mexico, Los Angeles, local). Extreme temperature fluctuations (hot during the day and cold during the night) led to difficulties with the triggering of the LDI laser on the ATOFMS, thereby limiting the continuity of the dataset. This only was the second field study conducted with the transportable ATOFMS, so progress was still being made in testing the ruggedness of some of the components on the instrument under true field conditions. However, in spite of these difficulties, information on the general major particle types in the PM2.5 fraction was obtained during the study. These particles included various forms of dust (with substantial processing by sulfates and nitrates), highly reacted salt particles with sulfates and nitrates, wood smoke, and vehicular exhaust. A strong dependence on wind direction was observed; when the wind blew from the west, significant associations between the particles and nitrates were observed. When the wind blew from the east, the associations shifted from nitrate transformation to sulfate associations.
There are implications associated with the relatively high levels of salt particles observed in the fine (< 2.5 micron) size fraction. Similar to other types of dust particles, the majority of the salt particles were coupled with nitrates, sulfates, and carbonates, which would enhance their light-scattering abilities. Furthermore, because these particles were salts, they readily would uptake water, and thus, their light-scattering properties would be strongly dependent on relative humidity. In addition to the general particle types, copper phosphate particles were detected, their presence showing a strong wind dependence; a local mining facility most likely produced this particle type. Other frequently observed metal particles during the study contained Zn and Pb. In addition, particles indicative of biomass burning were detected at various times during the study. These particles commonly were observed at nights after rain storms; this indicates that their most likely source was campfires in the area.
In summary, many of the particle types detected in the Grand Canyon area had signatures that could be used to relate them to vehicle, coal, and biomass emissions. Also, particles from local sources were evident. Further details on the Grand Canyon study will be obtained in the next year of this project.
In the Scripps study, the ATOFMS sampled particles during Santa Ana wind conditions in California. The objective of this project was to determine particle signatures in a marine environment. During the study, meteorological conditions (Santa Ana winds) induced a sudden change in particle concentrations and the associated composition. Specifically, PM primarily composed of organic carbon and sea salt changed to PM primarily composed of dust and organic particles, which were blown into the San Diego area from the desert regions. Such rapid changes in particle composition would be impossible to characterize with filter-based sampling methods, demonstrating the unique insights that can be gained by using online aerosol composition measurement techniques.
Future Activities:
The results of the Scripps Institution of Oceanography study are being analyzed and will be published in Atmospheric Environment. The analysis of the Grand Canyon dataset is continuing and ultimately, comparisons will be made with other measurements (i.e., bext, bscat, bulk chemical data) to provide insights into the mixing states of the particles and determine the resulting effect on visibility.
Journal Articles:
No journal articles submitted with this report: View all 23 publications for this projectSupplemental Keywords:
ambient air, air, aerosol, particulate matter, PM, measurement methods, western, sulfates, organics, mobile sources, tropospheric, marine, chemical transport, visibility, atmosphere, environmental chemistry, analytical, pollution, source allocation, real time, chemical analysis., RFA, Scientific Discipline, Air, particulate matter, Environmental Chemistry, Environmental Monitoring, Ecology and Ecosystems, tropospheric ozone, ambient aerosol, particle size, chemical characteristics, aerosol time-of-flight mass spectrometry (ATOFMS), ambient measurement methods, air pollution, air sampling, chemical composition, atmospheric transport, aerosol sampling, real time monitoring, ambient pollution control, chemical speciation sampling, particle transport, ambient aerosol particlesRelevant Websites:
Progress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.