Quantitative sampling using an Aerodyne aerosol mass spectrometer 1. Techniques of data interpretation and error analysis

Abstract

[1] The aerosol mass spectrometer (AMS), manufactured by Aerodyne Research, Inc., has been shown to be capable of delivering quantitative information on the chemical composition and size of volatile and semivolatile fine airborne particulate matter with high time resolution. Analytical and software tools for interpreting the data from this instrument and generating meaningful, quantitative results have been developed and are presented here with a brief description of the instrument. These include the conversion of detected ion rates from the quadrupole mass spectrometer during the mass spectrum (MS) mode of operation to atmospheric mass concentrations of chemical species (in mg m À3 ) by applying calibration data. It is also necessary to correct for variations in the electron multiplier performance, and a method involving the measurement of the instrument's response to gas phase signals is also presented. The techniques for applying particle velocity calibration data and transforming signals from time of flight (TOF) mode to chemical mass distributions in terms of aerodynamic diameter (dM/dlog(D a ) distributions) are also presented. It is also possible to quantify the uncertainties in both MS and TOF data by evaluating the ion counting statistics and variability of the background signal, respectively. This paper is accompanied by part 2 of this series, in which these methods are used to process and analyze AMS results on ambient aerosol from two U.K. cities at different times of the year.

Chemical composition of summertime aerosol in the Po Valley (Italy), northern Adriatic and Black Sea

“…straight and level runs) will be smaller, being inversely proportional to the square root of the averaging time. Information on Q-AMS ambient sampling , data quantification (Allan et al, 2003) and mass spectrum deconvolution can be found elsewhere. As well as mass loadings for various species, speciated mass size distributions and mass spectra (which can provide some information on the organic aerosol functionality; Zhang et al, 2005) are obtained.…”

“…This was accomplished by correcting the data using Equation (3), taken from Allan et al (2003), which corrects data for a reduction in gas phase nitrogen (the largest signal seen in the Q-AMS) due to a reduction in both electron multiplier performance throughout the flight, and also due to a reduction in mass flow rate into the instrument. AB 0 and Q 0 , and AB t and Q t represent the signal at m/z 28 (N 2 + ) and the mass flow rate at the time of IE calibration (preor post-flight) and at time t during measurement, and I t is the recorded signal at any m/z at a time t.…”

“…The calibration equation (Allan et al, 2003) to derive the particle vacuum aerodynamic from particle velocity (via the time of flight measurement) is shown in Equation (1), where v p is the measured particle velocity (m s −1 ), D a is the particle vacuum aerodynamic diameter (nm) (DeCarlo et al, 2004), and v l , v g , D * and b are derived as fitted parameters during calibration with Polystyrene Latex Spheres (PSLs), which are spherical particles of known size and density.…”

Characterization of aerosol associated with enhanced small particle number concentrations in a suburban forested environment

“…Ambient-pressure sample containing aerosol particles enters the instrument through a 130 mm critical orifice, after which particles are collimated using the aerodynamic focusing lens mentioned above [Liu et al, 1995a[Liu et al, , 1995b. Because of the transmission efficiency of this lens, the Q-AMS measures particles with vacuum aerodynamic diameters (D va ) between 40 nm and 1 mm; this measurement is typically referred to as submicron [Liu et al, 1995a[Liu et al, , 1995bJayne et al, 2000;Allan et al, 2003], although the range of 100% transmission of particles is 60 to 600 nm. No correction was applied to account for sub-100% transmission of particles with diameters smaller than 60 and greater than 600 nm.…”

Aerosol and trace‐gas measurements in the Darwin area during the wet season

“…This instrument employs thermal desorption, 70 eV electron ionization, and a quadrupole mass spectrometer. Data were processed and quality assured using the procedures described by Jimenez et al [2003] and Allan et al [2003Allan et al [ , 2004a and employed in conjunction with the pressuredependent calibrations and corrections described by Crosier et al [2006] needed for aircraft operation. Mass concentrations are reported from the Q-AMS (see section 5) for the total nitrate, organic, sulphate and ammonium component masses in the aerosol.…”