Contribution of Selected Dicarboxylic and ω-Oxocarboxylic Acids in Ambient Aerosol to them/z44 Signal of an Aerodyne Aerosol Mass Spectrometer

Abstract

The Aerodyne aerosol mass spectrometer (AMS) employs flash vaporization (600 • C) followed by 70-eV electron impact ionization (EI) to detect organic and inorganic aerosols. The signal at mass-to-charge ratio (m/z) 44 (mainly CO + 2 ) is considered the most reliable marker of oxygenated organic aerosol. This study is the first to evaluate the contribution of selected low molecular weight dicarboxylic acids (diacids) and ω-oxocarboxylic acids (ω-oxoacids) to the particle-phase m/z 44 signal of the AMS mass spectrum. Ambient measurements were conducted at a surface site in Tokyo (35• 39 N, 139• 40 E) during August 3-8, 2003. Diacids and ω-oxoacids were measured using a filter sampling followed by extraction, derivation, and gas chromatograph-flame ionization detector (GC-FID) analysis. The mass concentrations of diacids and ω-oxoacids show tight correlation with the m/z 44 signal (r 2 = 0.85-0.94) during the measurement period. Laboratory experiments were also performed to determine the fragment patterns of selected diacids (C 2 -C 6 diacids and phthalic acids) and ω-oxoacid (glyoxylic acid) in ambient aerosols. Here, we report for the first time that the selected organic acids could account for 14 ± 5% of the observed m/z 44 signal on average during the measurement period. Oxalic acid (C 2 ) is the largest contributor, accounting for 10 ± 4% of the observed m/z 44 signal. These results would be useful for interpreting the m/z 44 signals obtained from ambient measurements in various locations.

Estimating the contribution of organic acids to northern hemispheric continental organic aerosol

“…Relationships between m/z 44 and measurements of a few individual organic acids (rather than total particlephase acids) have also been observed in laboratory and field measurements [Takegawa et al, 2007;Sorooshian et al, 2010;Duplissy et al, 2011]. Takegawa et al [2007] observed good correlation (r 2 = 0.85-0.94) between m/z 44 and select dicarboxylic and ω-oxocarboxylic acids collected on filters in Tokyo, Japan.…”

“…Takegawa et al [2007] observed good correlation (r 2 = 0.85-0.94) between m/z 44 and select dicarboxylic and ω-oxocarboxylic acids collected on filters in Tokyo, Japan. Assuming that one of the carboxylic acid groups is detected as the CO 2 + ion, they noted that the measured diacids and oxoacids accounted for 14 ± 5% of the m/z 44 signal in ambient aerosol.…”

Performance of an Aerodyne Aerosol Mass Spectrometer (AMS) during Intensive Campaigns in China in the Summer of 2006

“…The thermodynamic parameters for these compounds were taken from the Chemical Dictionary (1994). The experimental apparatus was the same as that described by Takegawa et al (2007). The high voltage applied to the QMS detector (electron multiplier) was properly adjusted so that the m/z 39 signal was not saturated.…”

“…Takegawa et al (2007) estimated the average ratio of m/z 28 to m/z 44 to be 1.0 for Tokyo data during the summer of 2003 using particle time-of-flight data (P-ToF), in which m/z 28 signals from N + 2 and organics can be separated. Here we estimated the m/z 28 signal from organics using the same method as Takegawa et al (2007). We selected time periods with moderately or very high loadings of OM (11 cases for PRD and 15 cases for CAREBEIJING) and calculated the m/z 28 and 44 signals from organics using the P-ToF data.…”

“…It has been shown that m/z 28 could be an important peak for the quantification of organic compounds Takegawa et al 2007). Takegawa et al (2007) estimated the average ratio of m/z 28 to m/z 44 to be 1.0 for Tokyo data during the summer of 2003 using particle time-of-flight data (P-ToF), in which m/z 28 signals from N + 2 and organics can be separated. Here we estimated the m/z 28 signal from organics using the same method as Takegawa et al (2007).…”