In this work, an abundance of ice-nucleating particles (INPs) from livestock
facilities was studied through laboratory measurements from cloud-simulation chamber experiments and field investigation in the Texas Panhandle. Surface
materials from two livestock facilities, one in the Texas Panhandle and
another from McGregor, Texas, were selected as dust proxies for laboratory
analyses. These two samples possessed different chemical and biological
properties. A combination of aerosol interaction and dynamics in the
atmosphere (AIDA) measurements and offline ice spectrometry was used to
assess the immersion freezing mode ice nucleation ability and efficiency of
these proxy samples at temperatures above −29 ∘C. A dynamic
filter processing chamber was also used to complement the freezing
efficiencies of submicron and supermicron particles collected from the AIDA
chamber. For the field survey, periodic ambient particle sampling took place
at four commercial livestock facilities from July 2017 to July 2019. INP
concentrations of collected particles were measured using an offline
freezing test system, and the data were acquired for temperatures between −5 and −25 ∘C.
Our AIDA laboratory results showed that the freezing spectra of two
livestock dust proxies exhibited higher freezing efficiency than previously
studied soil dust samples at temperatures below −25 ∘C. Despite
their differences in composition, the freezing efficiencies of both proxy
livestock dust samples were comparable to each other. Our dynamic filter
processing chamber results showed on average approximately 50 %
supermicron size dominance in the INPs of both dust proxies. Thus, our
laboratory findings suggest the importance of particle size in immersion
freezing for these samples and that the size might be a more important factor for immersion freezing of livestock dust than the composition. From a
3-year field survey, we measured a high concentration of ambient INPs of 1171.6 ± 691.6 L−1 (average ± standard error) at −25 ∘C for aerosol particles collected at the downwind edges of
livestock facilities. An obvious seasonal variation in INP concentration,
peaking in summer, was observed, with the maximum at the same temperature exceeding 10 000 L−1 on 23 July 2018. The observed high INP
concentrations suggest that a livestock facility is a substantial source of
INPs. The INP concentration values from our field survey showed a strong
correlation with measured particulate matter mass concentration, which
supports the importance of size in ice nucleation of particles from
livestock facilities.</p