Can vibrational sum frequency scattering spectra be measured from the surface of 40-100 nm aerosols in a cloud containing 10$^{6}$ particles/mL?

TL;DR

This paper investigates the feasibility of measuring vibrational sum frequency scattering spectra from small aerosol particles, revealing that current methods are limited by detection sensitivity and proposing reasons for the discrepancy.

Contribution

The study quantifies the detection limits of vibrational sum frequency scattering for small aerosols and discusses reasons for the current measurement challenges.

Findings

SF scattering power of small particles is ~10^7 below detection limit

Theoretical and experimental detection limits are established

Possible reasons for measurement discrepancy are proposed

Abstract

Understanding the interfacial properties of aerosol particles is important for science and medicine, crucial for air quality, human health, and environmental chemistry. Qian et al. presented vibrational sum frequency scattering (SFS) measurements of organic molecules on aerosol particles.$^{1}$ Relating an aerosol sample with a 40 nm average size and 10 - 300 nm particle size distribution at a density of 10$^{6}$ particle/mL to vibrational sum frequency scattering spectra recorded in a different apparatus, it was concluded that the vibrational spectra reported on the surface structure of the particles in the aerosol. Here, we show that the SF scattering power of such small particles with a density of 10$^{6}$ particle/mL is $\sim$ 10$^{7}$ smaller than the detection limit of the presented SFS experiment. We determine the detectable number density of particles, both theoretically and experimentally, to demonstrate the limits of the SFS method. We also propose possible reasons for the 10$^{7}$ order of magnitude discrepancy.