EXTreme RAnge (EXTRA) reaction chamber
The EXTRA chamber is a 125 L stainless steel chamber whose walls have been coated with PFA to minimize wall loss of radicals. Six sample ports are located at either end of the chamber for connection to an ADS-GC-MS, a dual GC-ECD/FID system, CIMS and commercial sensors such as Thermo Electron Corporation 49i Ozone Analyzer, Edinburgh Instruments Gascard CO2 sensor and Trace Analytical inc. RGA3 CO analyzer. Unlike the majority of chambers, we can also measure the rate coefficients as a function of temperature and pressure. The EXTRA chamber can be operated at pressures from 10- 3800 Torr and at temperatures from 180 – 395 K. The multi-analytical approach enables the simultaneous detection of both radical and stable transient species, i.e. to enable the mass balance of reactions to be quantified and thus allow the full atmospheric importance of the reaction to be assessed.
Semi-volatile organic compounds (SVOCs) present a particular challenge to kinetic studies. At ambient temperatures, the loss of reaction material to chamber walls and particle formation can produce erroneous rate constant measurements. Therefore, experiments using the EXTRA chamber were conducted at elevated temperatures of ~394 K (McGillen er al., 2011).
Here the effect of increasing carbon number on the ozonolysis reaction rate constants of a homologous series of terminal alkenes (C8 – C14) was investigated:
Reaction kinetics were determined by GC-FID using the relative rate method. The ozonolysis reaction rate of terminal alkenes was therefore found to be invariant with carbon chain length, as shown in Figure 1. The same experimental methodology is also currently being applied to probe the reactivity of atmospherically important compounds of biogenic origin, such as sesquiterpenes.
References
McGillen et al., PCCP, 23, 10965-10969, 2011