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Reduced Ultrafine Particle Concentration in Urban Air: Changes in Nucleation and Anthropogenic Emissions
journal contribution
posted on 2018-05-18, 00:00 authored by Provat
K. Saha, Ellis S. Robinson, Rishabh U. Shah, Naomi Zimmerman, Joshua S. Apte, Allen L. Robinson, Albert A. PrestoNucleation is an important source
of ambient ultrafine particles
(UFP). We present observational evidence of the changes in the frequency
and intensity of nucleation events in urban air by analyzing long-term
particle size distribution measurements at an urban background site
in Pittsburgh, Pennsylvania during 2001–2002 and 2016–2017.
We find that both frequency and intensity of nucleation events have
been reduced by 40–50% over the past 15 years, resulting in
a 70% reduction in UFP concentrations from nucleation. On average,
the particle growth rates are 30% slower than 15 years ago. We attribute
these changes to dramatic reductions in SO2 (more than
90%) and other pollutant concentrations. Overall, UFP concentrations
in Pittsburgh have been reduced by ∼48% in the past 15 years,
with a ∼70% reduction in nucleation, ∼27% in weekday
local sources (e.g., weekday traffic), and 49% in the regional background.
Our results highlight that a reduction in anthropogenic emissions
can considerably reduce nucleation events and UFP concentrations in
a polluted urban environment.