Key Factors Determining Heterogeneous Uptake Kinetics of NO<sub>2</sub> Onto Alumina: Implication for the Linkage Between Laboratory Work and Modeling Study
Xiaoyan Gao, Cheng Zhong, Mingjin Tang, Qingxin Ma, Chang Liu
Abstract
Abstract Heterogeneous 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 NO 2 on surfaces of typical mineral component alumina ( α ‐Al 2 O 3 , γ ‐Al 2 O 3 , δ ‐Al 2 O 3 , 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 ( γ BET ) obtained via two techniques was within 1–2 orders of magnitude for alumina samples. The γ BET depended positively on NO 2 concentration in the DRIFTS measurements but negatively on NO 2 concentration in the flow tube experiments, and the discrepancy might be attributed to different calculation methods of γ BET , which was calculated based on nitrate formation kinetics in DRIFTS experiments while based on NO 2 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.