The Optical Properties of Limonene Secondary Organic Aerosols: The Role of NO₃, OH, and O₃ in the Oxidation Processes

Abstract

Limonene, a typical proxy of monoterpenes emitted from biogenic sources, plays an important role in secondary organic aerosol (SOA) formation. However, the optical properties of SOA generated from limonene under various oxidation pathways remain poorly understood. In this study, we investigate the refractive index (RI) of limonene SOA produced from four oxidation conditions with cavity ring‐down spectrometer (CRDS) and photoacoustic extinctiometer operated at 532 and 375 nm. Our results show that there is a significant difference in RI values of SOA produced from NO3 oxidation compared to other oxidation pathways. The mean values of RI of SOA produced from NO3 oxidation, NOx oxidation, OH oxidation with NOx‐free, and O3 oxidation experiments are 1.578, 1.469, 1.495, and 1.494 at 532 nm; and 1.591, 1.527, 1.513, and 1.537 at 375 nm, respectively, while no detectable absorption is found in all oxidation conditions. We attribute the high RI values of SOA by NO3 oxidation to two factors: a large proportion of organic nitrates and high‐molecular‐weight dimers/oligomers in the SOA. Our study results indicate that the nighttime chemistry may significantly influence the optical properties of limonene oxidation products. The RI values of limonene SOA generated under various oxidation conditions at different wavelengths retrieved in our laboratory experiments could help improve the model predictions for evaluating the effect of biogenic SOA on the global radiative forcing as well as climate change.

Effects of SO<sub>2</sub> on optical properties of secondary organic aerosol generated from photooxidation of toluene under different relative humidity

“…As the reaction proceeded, surface mean diameter of particles increased while n decreased. This phenomenon was observed in all experiments in this study and agreed well with previous studies (Li et al, 2014;Li et al, 2017b;Peng et al, 2018).…”

“…CC BY 4.0 License. et al, 2014;Li et al, 2017b;Li et al, 2017c;Li et al, 2018b;Peng et al, 2018;Li et al, 2018a). Briefly, the extinction coefficients (α ext ) at 532 nm measured by CRDS and the scattering, absorption, and extinction https://doi.org/10.5194/acp-2019-540 Preprint.…”

“…It would cause acceptable small errors for using it at 532 nm. This method was employed in our 20 previous as well (Li et al, 2017b;Li et al, 2018b;Li et al, 2017c;Peng et al, 2018).…”

A review of experimental techniques for aerosol hygroscopicity studies

“…Cavity ring-down spectroscopy (CRDS), a highly sensitive method for optical extinction measurement, has been extensively employed for gas and aerosol detection (Brown, 2003;Baynard et al, 2006;Baynard et al, 2007;Langridge et al, 2011;Sobanski et al, 2016;Peng et al, 2018). For a typical CRDS set-up, a laser beam pulse is coupled into a high-finesse optical cavity (which has one high reflectivity mirror on each end) from one end of the cavity, and the decay of the intensity of the light transmitted from the other end is monitored.…”

Effects of Aerosols on the Precipitation of Convective Clouds: A Case Study in the Yangtze River Delta of China

“…Airborne aerosols play an important role in the processes of atmospheric physics, chemistry, optics, and photochemistry (Mills et al, 2017;Peng et al, 2018). By scattering and absorbing solar radiation or acting as cloud condensation nuclei (CCN), atmospheric aerosols can have major impacts on air quality and climate change and further affect human health (Lohmann, 2017;McNeill, 2017;Rennó et al, 2013;Zheng et al, 2015).…”