4 research outputs found
External trade monthly statistics 1/1988/Commerce exterieur statistiques mensuelles 1988.1
In
urban environments, airborne particles are continuously emitted,
followed by atmospheric aging. Also, particles emitted elsewhere,
transported by winds, contribute to the urban aerosol. We studied
the effective density (mass-mobility relationship) and mixing state
with respect to the density of particles in central Copenhagen, in
wintertime. The results are related to particle origin, morphology,
and aging. Using a differential mobility analyzer-aerosol particle
mass analyzer (DMA-APM), we determined that particles in the diameter
range of 50–400 nm were of two groups: porous soot aggregates
and more dense particles. Both groups were present at each size in
varying proportions. Two types of temporal variability in the relative
number fraction of the two groups were found: soot correlated with
intense traffic in a diel pattern and dense particles increased during
episodes with long-range transport from polluted continental areas.
The effective density of each group was relatively stable over time,
especially of the soot aggregates, which had effective densities similar
to those observed in laboratory studies of fresh diesel exhaust emissions.
When heated to 300 °C, the soot aggregate volatile mass fraction
was ∼10%. For the dense particles, the volatile mass fraction
varied from ∼80% to nearly 100%