We propose a new application of inexpensive light-emitting diode (LED)-based Sun
photometers, consisting of measuring the aerosol optical thickness (AOT) with high resolution within
metropolitan scales. Previously, these instruments have been used at continental scales by the GLOBE
program, but this extension is already covered by more expensive and higher-precision instruments of the
AERONET global network. For this we built an open source two-channeled LED-based Sun photometer
based on previous developments, with improvements in the hardware, software, and modifications on
the calibration procedure. Among these we highlight the use of MODTRAN to characterize the effect
introduced by using LED sensors in the AOT retrieval, an open design available for the scientific community
and a calibration procedure that takes advantage of a CIMEL Sun photometer located within the city,
enables the intercomparison of several LED Sun photometers with a common reference. We estimated the
root-mean-square error in the AOT retrieved by the prototypes as 0.006 at the 564 nm and 0.009 at the
408 nm. This error is way under the magnitude of the AOT daily cycle variability measured by us in our
campaigns, even for distances closer than 15 km. In addition to inner city campaigns, we also show
aerosol-tracing applications by measuring AOT variations from the city of Santiago to the Andes glaciers.
Measuring AOT at high spatial resolution in urban areas can improve our understanding of urban scale
aerosol circulation, providing information for solar energy planning, health policies, and climatological
studies, among others.