Grantee Research Project Results
Final 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 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 involved 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 number 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 of this research project involves establishing how particle size and composition vary in different regions of the United States. Single-particle signatures provide unique insight into aging/chemistry and sources of particles. These studies represent the first extensive single-particle continuous monitoring field studies, so 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 to further our understanding of aerosol chemistry on shorter time scales. The original objectives of this research project were modified slightly when the U.S. Environmental Protection Agency (EPA) Particulate Matter (PM) Supersites Program began. Originally, ATOFMS was going to be used for PM sampling primarily in California, but when the EPA Supersites Program began, this was viewed as a unique opportunity to perform research on PM in various air masses with unique chemistry across the United States, with the added benefit of having other state-of-the-art PM and gas-phase measurements made simultaneously.
Summary/Accomplishments (Outputs/Outcomes):
The results of these field studies conducted in various locations in the United States show a distinct change in particle composition at 1 µm (see Figure 1 in full final report). This break has been shown to separate contributions from particles produced by anthropogenic combustion sources (e.g., biomass and vehicular emissions) from natural aerosol sources (e.g., dust and sea salt). An example of a location where this may not be the case is the Southeastern United States, where reactions of biogenically (natural [terpene] organics from local vegetation) plus anthropogenically (gas-phase oxidants) emitted species may form organic particles, which make significant contributions to the sub-µm size mode. The size-composition relationship observed in these studies as well as other studies conducted around the world with ATOFMS could be used by EPA to support establishing a new (additional) size cut for ambient monitoring of PM, because the same trends are observed for all locations in the United States. Using a cutpoint at 1 µm may ultimately allow for more appropriate control strategies to be established for PM in the United States. A 1-µm cutpoint may be particularly useful in areas where suspended dust contributes to the current fine particle fraction (PM2.5). Because particles from different sources (i.e., dust versus combustion) have been shown to induce different health effects, at the very least, this size cut could be used for more refined health effects studies. For example, one could simultaneously compare exposure to concentrated ambient particles from the same ambient air sampled using different size cuts (PM1 versus PM2.5). Currently, major uncertainties exist as to whether fine or coarse particles produce the largest health effects; this may be due to the ambiguity associated with the dramatically different compositions/sources contributing to PM2.5, depending on location and/or time of sampling. If a new standard were to be implemented, one consideration in certain areas (and at certain times of the year) is that the size cut between sources can shift to larger sizes at high relative humidity. However, this effect can be minimized by sampling at controlled relative humidities (i.e., 55 percent), as we have done in recent field studies.
We obtained mass spectral signatures of single particles in the Northeastern, Southeastern, Western, and Central regions of the United States. We used Micro-Orifice Uniform Deposit Impactor (MOUDI) scaling methods developed originally for California field studies for the quantification of PM mass, sulfates, nitrates, and ammonium. Ultimately, these datasets will be ideally suited for deriving similar scaling functions for elemental carbon and organic carbon, upon comparison of ATOFMS data with semicontinuous measurements made with higher time resolution. As part of this project, ATOFMS scaling procedures were derived using number concentration data from aerodynamic particle sizers (APS). As opposed to MOUDI impactor scaling, these factors provide higher time resolution and do not require assumptions (i.e., particle density). It was determined that shorter (simultaneously acquired) time scaling functions produce higher correlations. However, MOUDI scaling allows for the relative chemical sensitivity of the ATOFMS to be established for different chemical species upon comparison of the scaling factors for mass concentrations of different chemical species. This may ultimately be possible by scaling the ATOFMS data with other semicontinuous instruments.
We demonstrated the potential for using ATOFMS mass spectral signatures for source apportionment as well as studying the dynamics of particle transformations. We tested the universality of ATOFMS scaling procedures at different locations. Only in Atlanta was a different method required due to the abundance of relatively pure ammonium sulfate particles, which resulted in a chemical bias. We also obtained strong correlations between high temporal resolution-scaled ATOFMS data and tapered element oscillating microbalance mass concentrations, APS number concentrations, nephelometer (i.e., bscat), gas-phase, meteorological, sulfate, carbon, and nitrate mass concentrations. We measured temporal profiles of single-particle types, detecting rapid bursts (10-30 minutes) in the number concentrations of specific particles types including those containing metals, polycyclic aromatic hydrocarbons, and coal combustion. We measured the size-composition relationship for general particle types, similar to that observed in previous studies in California with division at 1 µm separating particles primarily composed of organic (i.e., combustion) versus inorganic (i.e., mechanically generated) species. This break was observed in all regions studied. Dust, sea salt, and organic particles on the west coast show substantial processing by nitrates, whereas on the east coast, particles are more commonly coupled with sulfates, consistent with previous filter-based studies. In general, nitrate shows strong diurnal variations, whereas sulfate occurs with less diurnal variability. We measured the mixing state of particles in the Grand Canyon, which will ultimately be used to examine the effect of particle composition on visibility and reduce the uncertainty in the extinction budget.
The first extended field studies have seen a number of key advances in ATOFMS technology, providing faster sampling times, wider dynamic range of ion detection, and a number of other advances. In addition, a great deal has been learned about data analysis. The next steps are to try more advanced data analysis tools (i.e., ones that can analyze particles on the fly) and source apportionment (i.e., multivariate) tools to determine regional PM sources and their influence on human health and local environmental processes. Furthermore, now that single-particle data have been reduced from size composition on millions of particles into actual concentrations of different particle types, it is in a format that will allow for comparison with regional and global models.
Journal Articles on this Report : 5 Displayed | Download in RIS Format
Other project views: | All 23 publications | 5 publications in selected types | All 5 journal articles |
---|
Type | Citation | ||
---|---|---|---|
|
Angelino S, Suess DT, Prather KA. Formation of aerosol particles from reactions of secondary and tertiary alkylamines: characterization by aerosol time-of-flight mass spectrometry. Environmental Science & Technology 2001;35(15):3130-3138. |
R826240 (2001) R826240 (Final) |
Exit |
|
Guazzotti SA, Whiteaker JR, Suess D, Coffee KR, Prather KA. Real-time measurements of the chemical composition of size-resolved particles during a Santa Ana wind episode, California USA. Atmospheric Environment 2001;35(19):3229-3240. |
R826240 (2001) R826240 (Final) |
Exit Exit Exit |
|
Liu D-Y, Wenzel RJ, Prather KA. Aerosol time-of-flight mass spectrometry during the Atlanta Supersite Experiment:1. Measurements. Journal of Geophysical Research: Atmospheres 2003;108(D7):8426. |
R826240 (2002) R826240 (Final) |
Exit Exit Exit |
|
Middlebrook AM, Murphy DM, Lee S-H, Thomson DS, Prather KA, Wenzel RJ, Liu D-Y, Phares DJ, Rhoads KP, Wexler AS, Johnston MV, Jimenez JL, Jayne JT, Worsnop DR, Yourshaw I, Seinfeld JH, Flagan RC. A comparison of particle mass spectrometers during the 1999 Atlanta Supersite Project. Journal of Geophysical Research: Atmospheres 2003;108(D7):8424. |
R826240 (2002) R826240 (Final) |
Exit Exit Exit |
|
Wenzel RJ, Liu D-Y, Edgerton ES, Prather KA. Aerosol time-of-flight mass spectrometry during the Atlanta Supersite Experiment: 2. scaling procedures. Journal of Geophysical Research: Atmospheres 2003;108(D7):8427. |
R826240 (2002) R826240 (Final) |
Exit Exit |
Supplemental Keywords:
air, aerosol, particulate matter, PM, measurement methods, Southeast, Western, Eastern, sulfates, organics, mobile sources, tropospheric, marine, chemical transport, visibility, ambient air, atmosphere, environmental chemistry, analytical, pollution, source allocation, real-time, chemical analysis., RFA, Scientific Discipline, Air, particulate matter, Environmental Chemistry, Environmental Monitoring, tropospheric ozone, Ecology and Ecosystems, 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:
http://atofms.ucsd.edu Exit
http://www.yaada.org Exit
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.