An experimental technique for the direct measurement of N2O5 reactivity on ambient particles

摘要

An experimental approach for the direct measurement of trace gas reactivityon ambient aerosol particles has been developed. The method utilizes a newlydesigned entrained aerosol flow reactor coupled to a custom-built chemicalionization mass spectrometer. The experimental method is described viaapplication to the measurement of the NO reaction probability,γ (NO). Laboratory investigations on well characterizedaerosol particles show that measurements of γ (NO) observedwith this technique are in agreement with previous observations, usingconventional flow tube methods, to within ±20% at atmosphericallyrelevant particle surface area concentrations(0–1000 μm cm). Uncertainty in the measuredγ (NO) is discussed in the context of fluctuations inpotential ambient biases (e.g., temperature, relative humidity and trace gasloadings). Under ambient operating conditions we estimate a single-pointuncertainty in γ (NO) that ranges between± (1.3×10 + 0.2×γ (NO)), and± (1.3×10 + 0.2×γ (NO)) forparticle surface area concentrations of 100 to 1000 μm cm,respectively. Examples from both laboratory investigations and fieldobservations are included alongside discussion of future applications for thereactivity measurement and optimal deployment locations and conditions.