2 research outputs found
Identification of the Sources and Geographic Origins of Black Carbon using Factor Analysis at Paired Rural and Urban sites
Black carbon particles,
composed of forms of elemental carbon (EC),
contribute significantly to regional and global warming. The origins
of EC were examined in southeastern Canada as part of a source apportionment
study using positive matrix factorization (PMF), performed on long-term
PM<sub>2.5</sub> chemical speciation data collected at two paired
rural and urban sites. Comparisons of the urban and rural sites revealed
a previously unrecognized EC-rich factor that accounted for 41–56%
of the total EC in this region. This factor was characterized by the
more thermally stable EC fractions that exhibit strong light absorption
characteristics. While these EC fractions are often attributed to
local diesel emissions, this interpretation was rejected for several
reasons. The EC-rich factor was present in similar temporal patterns
at both the high-traffic urban and low-traffic rural sites across
this 600 km region. The geographic origins of the EC-rich factor were
found to be Ohio and Western Pennsylvania regions with heavy industry
and multiple coal-based electrical generating stations. The direct
radiative forcing due to this EC-rich factor was roughly estimated
to be +0.2 W m<sup>–2</sup>, which represented a substantial
portion of the aerosol induced warming in the region. Thus, this region
was impacted by an important unidentified source of EC associated
with long-range transport
Near-Road Air Pollutant Measurements: Accounting for Inter-Site Variability Using Emission Factors
A daily integrated emission factor
(EF) method was applied to data from three near-road monitoring sites
to identify variables that impact traffic related pollutant concentrations
in the near-road environment. The sites were operated for 20 months
in 2015–2017, with each site differing in terms of design,
local meteorology, and fleet compositions. Measurement distance from
the roadway and local meteorology were found to affect pollutant concentrations
irrespective of background subtraction. However, using emission factors
mostly accounted for the effects of dilution and dispersion, allowing
intersite differences in emissions to be resolved. A multiple linear
regression model that included predictor variables such as fraction
of larger vehicles (>7.6 m in length; i.e., heavy-duty vehicles),
vehicle speed, and ambient temperature accounted for intersite variability
of the fleet average NO, NO<sub><i>x</i></sub>, and particle
number EFs (R<sup>2</sup>:0.50–0.75), with lower model performance
for CO and black carbon (BC) EFs (R<sup>2</sup>:0.28–0.46).
NO<sub><i>x</i></sub> and BC EFs were affected more than
CO and particle number EFs by the fraction of larger vehicles, which
also resulted in measurable weekday/weekend differences. Pollutant
EFs also varied with ambient temperature and because there were little
seasonal changes in fleet composition, this was attributed to changes
in fuel composition and/or post-tailpipe transformation of pollutants