Key Factors Determining Heterogeneous Uptake Kinetics of NO2 Onto Alumina: Implication for the Linkage Between Laboratory Work and Modeling Study

Abstract

AbstractHeterogeneous reactions on mineral dust play pivotal roles in the removal/production of gaseous pollutants and the formation of secondary particles. However, the uptake coefficient (γ), a key kinetic parameter for a heterogeneous reaction, could vary by several orders of magnitude in different laboratory analyses and give rise to great uncertainties in modeling studies. Thus, a detailed understanding of heterogeneous uptake kinetics is vital to accurately evaluate the impacts of heterogeneous reactions on atmospheric chemistry. In order to reveal the key factors affecting uptake kinetics, heterogeneous reaction of NO2 on surfaces of typical mineral component alumina (α‐Al2O3, γ‐Al2O3, δ‐Al2O3, and AlOOH) was comprehensively studied using two widely used methods, including diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and flow tube reactor. The discrepancy between the true uptake coefficients (γBET) obtained via two techniques was within 1–2 orders of magnitude for alumina samples. The γBET depended positively on NO2 concentration in the DRIFTS measurements but negatively on NO2 concentration in the flow tube experiments, and the discrepancy might be attributed to different calculation methods of γBET, which was calculated based on nitrate formation kinetics in DRIFTS experiments while based on NO2 consumption kinetics in flow tube experiments. The results implied that an accurate selection of the uptake coefficient for modeling studies should base on the consideration of factors such as the measurement method, the concentration range of the reaction gas, and the characteristics of the sample such as crystal structure and effective surface area.