Web Release Date: October 19,
A Field-Based Approach for Determining ATOFMS Instrument Sensitivities to Ammonium and Nitrate
Department of Environment Science and Engineering, California Institute of Technology, Pasadena, California 91125-7800
Departments of Chemical & Materials Engineering and Civil & Environmental Engineering, Arizona State University, Tempe, Arizona 82876-6006
and
Department of Chemistry, University of California, Riverside, Riverside, California 92521
School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia 39332-0340
Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093-0314
Received for review December 3, 2001
Revised manuscript received July 25, 2002
Accepted August 21, 2002
Abstract:
Aerosol time-of-flight mass spectrometry (ATOFMS)
instruments measure the size and chemical composition
of individual particles in real-time. ATOFMS chemical
composition measurements are difficult to quantify, largely
because the instrument sensitivities to different chemical
species in mixed ambient aerosols are unknown. In this
paper, we develop a field-based approach for determining
ATOFMS instrument sensitivities to ammonium and
nitrate in size-segregated atmospheric aerosols, using
tandem ATOFMS-impactor sampling. ATOFMS measurements
are compared with collocated impactor measurements
taken at Riverside, CA, in September 1996, August 1997, and
October 1997. This is the first comparison of ion signal
intensities from a single-particle instrument with quantitative
measurements of atmospheric aerosol chemical composition.
The comparison reveals that ATOFMS instrument
sensitivities to both 
and 
decline with increasing
particle aerodynamic diameter over a 0.32-1.8 
m
calibration range. The stability of this particle size dependence
is tested over the broad range of fine particle concentrations
(PM1.8 = 17.6 ± 2.0-127.8 ± 1.8 g m-3), ambient
temperatures (23-35 
C), and relative humidity conditions
(21-69%), encountered during the field experiments. This
paper describes a potentially generalizable methodology
for increasing the temporal and size resolution of atmospheric
aerosol chemical composition measurements, using
tandem ATOFMS-impactor sampling.
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