A low-cost particulate matter (PM 2.5 ) monitor for wildland fire smoke
Abstract. Wildfires and prescribed fires produce emissions that degrade
visibility and are harmful to human health. Smoke emissions and
exposure monitoring is critical for public and environmental health
protection; however, ground-level measurements of smoke from
wildfires and prescribed fires has proven difficult, as existing
(validated) monitoring technologies are expensive, cumbersome, and
generally require line power. Few ground-based measurements are made
during fire events, which limits our ability to assess the
environmental and human health impacts of wildland fire smoke. The objective of this work was to develop and validate an Outdoor
Aerosol Sampler (OAS) – a filter-based air sampler that has been
miniaturized, solar powered, and weatherproofed. This sampler was
designed to overcome several of the technical challenges of wildland
fire monitoring by being relatively inexpensive and solar
powered. The sampler design objectives were achieved by leveraging
low-cost electronic components, open-source programming platforms,
and in-house fabrication methods. A direct-reading PM2.5 
sensor was selected and integrated with the OAS to provide
time-resolved concentration data. Cellular communications
established via short message service (SMS) technology were utilized
in transmitting online sensor readings and controlling the sampling
device remotely. A Monte Carlo simulation aided in the selection of
battery and solar power necessary to independently power the OAS,
while keeping cost and size to a minimum. Thirteen OAS were deployed to monitor smoke concentrations downwind
from a large prescribed fire. Aerosol mass concentrations were
interpolated across the monitoring network to depict smoke
concentration gradients in the vicinity of the fire. Strong
concentration gradients were observed (spatially and temporally) and
likely present due to a combination of changing fire location and
intensity, topographical features (e.g., mountain ridges), and
diurnal weather patterns. Gravimetric filter measurements made by
the OAS (when corrected for filter collection efficiency) showed
relatively good agreement with measurements from an EPA federal
equivalent monitor. However, the real-time optical sensor (Sharp
GP2Y1023AU0F, Sharp Electronic Co.) within the OAS suffered from
temperature dependence, drift, and imprecision.