Chemical Ionization Mass Spectrometer Instrument for the Measurement of Tropospheric HO₂and RO₂

Abstract

Laboratory characterizations of the peroxy radical chemical ionization mass spectrometer (PerCIMS) instrument have been performed. The instrument functions by drawing ambient air through a 50-microm-diameter orifice into an inlet held at low pressure. Peroxy radicals (HO2 and RO2) within this air are detected by amplified chemical conversion into a unique ion (HSO4-) via the chemistry initiated by the addition of NO and SO2 to the inlet. HSO4- ions are then quantified by a quadrupole filter mass spectrometer. PerCIMS provides measurements of the sum of peroxy radicals, HO2 + RO2 (HOxROx mode), or the HO2 component only (HO2 mode), achieved through the control of concentration of NO and SO2 added to the instrument. The characterization and response of this instrument have been evaluated through modeling of inlet chemistry and laboratory experiments and have also been demonstrated through successful deployment during field campaigns. The performance of PerCIMS with respect to calibration pressure and relative humidity is reported, as are the sensitivities of the instrument to organic peroxy radicals with different hydrocarbon groups. These data show PerCIMS to be a practical field instrument for the fast and accurate evaluation of the concentration of peroxy radicals over a variety of atmospheric conditions. The estimated accuracy of the derived [HOxROx] concentrations is +/- 35% (at the 95% confidence interval), while [HO2] measurements have accuracies of +/- 41% (at the 95% confidence interval). Typical precision of measurements well above the detection limit is 10%, and typical detection limits are 1 x 10(7) radicals cm(-3) for 15-s averaging times.

Biogenic emission measurement and inventories determination of biogenic emissions in the eastern United States and Texas and comparison with biogenic emission inventories

“…[11] Sulfuric acid (H 2 SO 4 ) was measured during ICARTT2004 and TexAQS2006 using a chemical ionization mass spectrometer (CIMS) [Edwards et al, 2003;Tanner et al, 1997]. The uncertainty in the sulfuric acid measurement is about 40%.…”

Design of and initial results from a Highly Instrumented Reactor for Atmospheric Chemistry (HIRAC)

“…Immediately prior to the air entering the wand a small flow is diverted to a dew point hygrometer (CR4, Buck Research Instrument) to measure the concentration of water vapour in the flow. The product of the photon flux and the photolysis exposure time as a function of lamp current is determined using NO actinometry (Edwards et al, 2003), which allows a determination of F 184.9 nm and t according to the following relation: (Edwards et al, 2003). The uncertainty for the actinometry is ±13% (1 σ ), and the total calibration uncertainty is ±23% (1 σ ).…”

Detection of HO<sub>2</sub> by laser-induced fluorescence: calibration and interferences from RO<sub>2</sub> radicals

“…It applies chemical conversion of HO 2 to OH at reduced pressure and detects OH by LIF (see review, Heard and Pilling, 2003). Chemical conversion combined with radical amplification H. Fuchs et al: HO 2 by LIF: calibration and interference from RO 2 is used by Peroxy Radical Chemical Amplifier (PERCA) (Cantrell et al, 1984;Hastie et al, 1991;Clemitshaw et al, 1997;Burkert et al, 2001;Sadanaga et al, 2004;Mihele and Hastie, 2000;Green et al, 2006;Andrés-Hernández et al, 2010) and Peroxy Radical Chemical-Ionization Mass Spectrometry (ROxMas, PerCIMS) (Hanke et al, 2002;Edwards et al, 2003;Hornbrook et al, 2011), in order to achieve high measurement sensitivities for HO 2 . All indirect techniques (LIF, PERCA and ROxMas/PerCIMS) make use of the conversion reaction between HO 2 and NO, in order to produce OH.…”

“…The HO 2 measurement mode requires good suppression of the RO 2 to HO 2 conversion. Edwards et al (2003), for example, achieved a suppression to less than 15 % in their PerCIMS instrument for RO 2 species that were produced by the reaction of Cl with various hydrocarbons. However, this required large changes in concentrations of reactants, so that the modulation between HO 2 and RO x measurement mode took 30 min.…”

“…The new method that improves temporal resolution offers good discrimination between HO 2 and various alkyl peroxy radicals, but RO 2 from the reaction of OH with large alkanes, alkenes (including isoprene) and aromatics are partially or fully detected in the HO 2 -mode of this instrument. RO 2 radicals were produced by the reaction of OH in Hornbrook et al (2011), so that radical species from the same organic precursor were not necessarily the same as in Edwards et al (2003).…”