CCN production by new particle formation in the free troposphere
Global models predict that new particle formation (NPF) is, in some environments, responsible for a substantial fraction of the total atmospheric particle number concentration and subsequently contributes significantly to cloud condensation nuclei (CCN) concentrations. NPF events were frequently obs...
| Main Authors: | , , , , , , , , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2017-01-01
|
| Series: | Atmospheric Chemistry and Physics |
| Online Access: | http://www.atmos-chem-phys.net/17/1529/2017/acp-17-1529-2017.pdf |
| Summary: | Global models predict that new particle formation (NPF) is, in some
environments, responsible for a substantial fraction of the total
atmospheric particle number concentration and subsequently contributes
significantly to cloud condensation nuclei (CCN) concentrations. NPF events
were frequently observed at the highest atmospheric observatory in the
world, on Chacaltaya (5240 m a.s.l.), Bolivia. The present study focuses on the
impact of NPF on CCN population. Neutral cluster and Air Ion Spectrometer
and mobility particle size spectrometer measurements were simultaneously
used to follow the growth of particles from cluster sizes down to
∼ 2 nm up to CCN threshold sizes set to 50, 80 and 100 nm.
Using measurements performed between 1 January and 31 December 2012, we
found that 61 % of the 94 analysed events showed a clear particle growth
and significant enhancement of the CCN-relevant particle number
concentration. We evaluated the contribution of NPF, relative to the
transport and growth of pre-existing particles, to CCN size. The averaged
production of 50 nm particles during those events was 5072, and
1481 cm<sup>−3</sup> for 100 nm particles, with a larger contribution of NPF
compared to transport, especially during the wet season. The data set was
further segregated into boundary layer (BL) and free troposphere (FT)
conditions at the site. The NPF frequency of occurrence was higher in the BL
(48 %) compared to the FT (39 %). Particle condensational growth was
more frequently observed for events initiated in the FT, but on average
faster for those initiated in the BL, when the amount of condensable species
was most probably larger. As a result, the potential to form new CCN was
higher for events initiated in the BL (67 % against 53 % in the FT). In
contrast, higher CCN number concentration increases were found when the NPF
process initially occurred in the FT, under less polluted conditions. This
work highlights the competition between particle growth and the removal of
freshly nucleated particles by coagulation processes. The results support
model predictions which suggest that NPF is an effective source of CCN in
some environments, and thus may influence regional climate through cloud-related radiative processes. |
|---|---|
| ISSN: | 1680-7316 1680-7324 |