Grantee Research Project Results
1999 Progress Report: Real-time Measurement of the Size and Composition of Atmospheric Particulate Matter
EPA Grant Number: R826234Title: Real-time Measurement of the Size and Composition of Atmospheric Particulate Matter
Investigators: Wexler, Anthony S. , Johnston, Murray V.
Institution: University of Delaware
EPA Project Officer: Hahn, Intaek
Project Period: December 15, 1997 through December 14, 2000
Project Period Covered by this Report: December 15, 1998 through December 14, 1999
Project Amount: $374,833
RFA: Ambient Air Quality (1997) RFA Text | Recipients Lists
Research Category: Air Quality and Air Toxics , Air
Objective:
Although numerous studies show a correlation between PM2.5 (particulate matter) and health effects, the mechanism has not yet been elucidated. The atmosphere contains particles that range in size and composition. Establishing whether the health effects are due to size, composition, or a combination of both depends on developing an ability to measure these quantities for individual particles. The objective of this research is to develop and test an instrument that is able to analyze individual aerosol particles online and in real time in the respirable size range from 10 nm to 1 micron.Progress Summary:
We already had built an instrument that is able to analyze individual particles. Briefly, particles are drawn through a set of orifices that reduce the pressure of the gas and efficiently transmit the particles. The particles then pass through an orifice that focuses a selected size to the source region of a mass spectrometer. The pressure upstream of this second orifice governs the particle size that is focused. An excimer laser is free fired at about 80 Hz and directed co-linear to and opposite in direction from the particle beam. If a particle is in the source region of the TOF mass spectrometer when the laser fires, the particle is ablated and ionized, and the ions are analyzed.
Prototype Light Scattering Add-On Completed and Tested. There are more small particles in the atmosphere than larger ones. To increase the efficiency for sampling the larger particles, a light-scattering apparatus was built and field tested. With the light-scattering apparatus, the excimer laser pulse can be synchronized with the particle arrival, which only works with particles large enough to be detected by light scattering.
Improved Nozzle Completed. A new, improved focusing section was added to the current nozzle to make testing of alternate designs easier. The nozzle was calibrated in the laboratory, and an analytical expression was developed?in agreement with the laboratory tests?that relates the nozzle pressure to the particle size focused.
First Field Trial Completed. The instrument was transported to the Calspan smog chamber test facility in Ashland, NY. The Naval Research Laboratory was running aerosol dynamics tests at its laboratory and we used this opportunity to test the single particle instrument on both aerosols in the smog chamber and on rural ambient aerosols in the vicinity of the facility. From previous work, we knew that the aerosols must be dried to improve their analysis, and the diffusion dryers were not able to dry in high-humidity situations (see the next accomplishment).
Drier Completed. A Nafion drier was built and added to the system to: (1) remove the need to recharge the previous silica-based dryer, and (2) reduce the relative humidity to reasonable levels under fog and cloud conditions.
Preliminary Tests on Soot Completed. Soot is a potential culprit in the PM-health link. In collaboration with a combustion group in the Mechanical Engineering Department, we formed soot particles in the 5 nm to 50 nm size range and sampled them into the instrument. This allowed us to test the capabilities of the instrument for very small particles and to gain a better understanding of the spectra arising from analysis of soot particles.
Second Field Trial Completed. In August 1999, a portable laboratory was purchased and used to transport the instrument to Atlanta for the Atlanta Supersite measurements. Over 20,000 spectra were obtained, ranging from 17 nm to over 500 nm.
Flow/Pressure Controller. The flow and pressure were controlled with a bank of 10 critical orifices and a computer-controlled rotary valve to select the pressure/flow. There are few particle losses because the orifices are sharp and open into a relatively large chamber with very few surfaces on which the particle can impinge.
Software Development. Software has been developed to operate the instrument for extended periods of time so that data can be acquired without continuous operator intervention. Software also has been developed and is being improved to perform time-to-mass conversion of the spectra and to identify peaks in the spectra.
Future Activities:
Activities will include: improving negative ion analytical abilities, particle transmission efficiency, and light-scattering apparatus; completing soot tests; and building the Faraday cup nozzle test apparatus.Journal Articles on this Report : 2 Displayed | Download in RIS Format
Other project views: | All 10 publications | 5 publications in selected types | All 5 journal articles |
---|
Type | Citation | ||
---|---|---|---|
|
Mallina RV, Wexler AS, Johnston MV. High-speed particle beam generation: simple focusing mechanisms. Journal of Aerosol Science 1999;30(6):719-738. |
R826234 (1999) R826234 (Final) R823980 (Final) |
Exit |
|
Mallina RV, Wexler AS, Rhoads KP, Johnston MV. High speed particle beam generation: a dynamic focusing mechanism for selecting ultrafine particles. Aerosol Science and Technology 2000;33(1-2):87-104. |
R826234 (1999) R826234 (Final) |
Exit |
Supplemental Keywords:
ambient air, atmosphere, tropospheric, health effects, particulates, particulate matter, PM2.5, PAHs, PNAs, metals, heavy metals, sulfates, organics, monitoring, analytical, measurement methods., RFA, Scientific Discipline, Air, particulate matter, Environmental Chemistry, Environmental Monitoring, Atmospheric Sciences, particle size, particulates, PM10, mass spectrometer, fine particles, PM 2.5, field-portable instruments, Volatile Organic Compounds (VOCs)Relevant Websites:
http://www.me.udel.edu/wexler/spa_refs.html
http://www.me.udel.edu/~rhoads/
The first Web site contains references to all known publications related to online single particle analysis. Many investigators in the field use this site to keep up to date on the topic.
Because analysis of the Atlanta data is still in progress, the second Web site is the best reference for the current state of knowledge on the spectra obtained and their interpretation. Currently, it contains histograms of the data obtained by day, hour of day, and size range.
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.