Abstract. Environmental chambers are a commonly used tool for
studying the production and processing of aerosols in the atmosphere. Most
are located indoors and most are filled with air having prescribed
concentrations of a small number of reactive gas species. Here we describe
portable chambers that are used outdoors and filled with mostly ambient air.
Each all-Teflon® 1 m3 Captive Aerosol Growth and
Evolution (CAGE) chamber has a cylindrical shape that rotates along its
horizontal axis. A gas-permeable membrane allows exchange of gas-phase
species between the chamber and surrounding ambient air with an exchange
time constant of approximately 0.5 h. The membrane is non-permeable to
particles, and those that are injected into or nucleate in the chamber are
exposed to the ambient-mirroring environment until being sampled or lost to
the walls. The chamber and surrounding enclosure are made of materials that
are highly transmitting across the solar ultraviolet and visible wavelength
spectrum. Steps taken in the design and operation of the chambers to
maximize particle lifetime resulted in averages of 6.0, 8.2, and 3.9 h
for ∼ 0.06, ∼ 0.3, and
∼ 2.5 µm diameter particles, respectively. Two of the
newly developed CAGE chamber systems were characterized using data acquired
during a 2-month field study in 2016 in a forested area north of Houston,
TX, USA. Estimations of measured and unmeasured gas-phase species and of
secondary aerosol production in the chambers were made using a
zero-dimensional model that treats chemical reactions in the chamber and the
continuous exchange of gases with the surrounding air. Concentrations of NO,
NO2, NOy, O3, and several organic compounds measured in the
chamber were found to be in close agreement with those calculated from the
model, with all having near 1.0 best fit slopes and high r2 values. The
growth rates of particles in the chambers were quantified by tracking the
narrow modes that resulted from injection of monodisperse particles and from
occasional new particle formation bursts. Size distributions in the two
chambers were measured intermittently 24 h d−1. A bimodal diel
particle growth rate pattern was observed, with maxima of about
6 nm h−1 in the late morning and early evening and minima of less than 1 nm h−1 shortly before sunrise and sunset. A pattern change was observed
for hourly averaged growth rates between late summer and early fall.