ac6b03979_si_001.pdf (1.44 MB)
Coalescence Sampling and Analysis of Aerosols using Aerosol Optical Tweezers
journal contribution
posted on 2017-01-27, 00:00 authored by Allen
E. Haddrell, Rachael E. H. Miles, Bryan R. Bzdek, Jonathan P. Reid, Rebecca J. Hopkins, Jim S. WalkerWe present a first
exploratory study to assess the use of aerosol
optical tweezers as an instrument for sampling and detecting accumulation-
and coarse-mode aerosol. A subpicoliter aqueous aerosol droplet is
captured in the optical trap and used as a sampling volume, accreting
mass from a free-flowing aerosol generated by a medical nebulizer
or atomizer. Real-time measurements of the initial stability in size,
refractive index, and composition of the sampling droplet inferred
from Raman spectroscopy confirm that these quantities can be measured
with high accuracy and low noise. Typical standard deviations in size
and refractive index of the sampling droplet over a period of 200
s are <±2 nm and <±0.0005, respectively, equivalent
to <±0.04% in both measured quantities. A standard deviation
of <±1% over a 200 s period is achieved in the spontaneous
Raman intensity measurement. When sampling coarse-mode aerosol, mass
changes of <10 pg can be detected by the sampling droplet as discrete
coalescence events. With accumulation-mode aerosol, we show that fluxes
as low as 0.068 pg s–1 can be detected over a 50
s period, equivalent to ∼3 pg of sampled material.