Open AccessA calibrated peroxy radical chemical amplifier for ground‐based tropospheric measurements
Author(s) -
Clemitshaw Kevin C.,
Carpenter Lucy J.,
Penkett Stuart A.,
Jenkin Michael E.
Publication year - 1997
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/97jd01902
Subject(s) - radical , chemiluminescence , troposphere , calibration , environmental science , luminol , analytical chemistry (journal) , amplifier , meteorology , chemistry , physics , environmental chemistry , organic chemistry , cmos , optoelectronics , quantum mechanics
A calibrated peroxy radical chemical amplifier (PERCA) instrument has been developed at the University of East Anglia (UEA) and deployed in several recent field measurement campaigns. The UEA PERCA utilizes modulated chemical amplification of NO 2 by HO 2 and RO 2 radicals in the presence of 3.0 ppmv NO and 7.0% vol/vol CO, with the amplification factor or chain length approximately equal to ΔNO 2 /([H 2 ] + [RO 2 ]). NO 2 measurements and calibrations are made in the linear response regime of an improved Scintrex LMA‐3 NO 2 ‐luminol chemiluminescence detector with an estimated systematic uncertainty of ±10% and a precision of 5%. A novel calibration source of CH 3 O 2 radicals has been developed. It is used routinely during field campaigns to measure chain lengths of 175±15 for a new inlet system. The source is based upon 253.7 nm photolysis of CH 3 I in air and is capable of producing between 25 and 100 pptv CH 3 O 2 radicals. The detection limit of the PERCA varies from 0.2 to 2 pptv for a 30 min averaging time and is largely dependent upon the stability of the sum of the concentrations of ambient NO 2 and O 3 (O x ) which contribute to a background signal. The estimated systematic uncertainty in the measurements of HO 2 and RO 2 is ±30%. Observations of peroxy radicals made during the recent WAOWE'94 and WAOSE'95 field measurement campaign on the north Norfolk coast of England are presented to demonstrate the performance of the PERCA and are discussed briefly in terms of nighttime radical chemistry and net photochemical production of O 3 and peroxyacetyl nitrate (PAN).