 |
| Titel |
Spatial and vertical extent of nucleation events in the Midwestern USA: insights from the Nucleation In ForesTs (NIFTy) experiment |
| VerfasserIn |
S. C. Pryor, R. J. Barthelmie, L. L. Sørensen, J. G. McGrath, P. Hopke, T. Petäjä |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1680-7316
|
| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 11, no. 4 ; Nr. 11, no. 4 (2011-02-21), S.1641-1657 |
| Datensatznummer |
250009368
|
| Publikation (Nr.) |
 copernicus.org/acp-11-1641-2011.pdf |
|
|
|
|
|
| Zusammenfassung |
| Measurements of aerosol particle physical and chemical properties, gas phase
concentrations and meteorological parameters were made along a transect in
southern Indiana during the Nucleation In ForesTs (NIFTy) experiment
conducted in May 2008. These measurements indicate nucleation was observed
at all three measurement sites on almost half of all sampling days. The
intensity of the nucleation events, as measured by the increase in
≥10 nm aerosol particle number concentrations of approximately
2×104 cm−3 over a layer of at least 300 m depth, is in good
agreement with recent model results for the Midwestern USA derived using
PMCAMx-UF. During the hour after termination of nucleation approximately
half of the number concentration reduction is due to coagulation, while the
remainder is due in equal parts to dry deposition and entrainment of
relatively ultra-fine aerosol particle free troposphere air. Clear
nucleation with continuous subsequent growth is only observed on days when
the morning fractional cloud cover was less than 30%. It is associated
with a clear transition from a strongly stratified atmosphere with low
turbulence intensity and weak vertical velocities, to much a weaker vertical
gradient of wind speed, increased turbulence intensity and stronger
downwards vertical velocities, consistent with growth of the mixed layer and
entrainment of air from the residual layer. Nucleation intensity is not very
strongly determined by the prevailing condensational sink. However, there is
a strong correlation between both a modified version of the Nucleation
Parameter from Boy and Kulmala (2002) and ultrafine aerosol particle number
concentrations, and mean morning H2SO4 concentrations and
ultrafine aerosol particle number concentrations. Five A-class event days
during NIFTy were characterized by values of the dimensionless nucleation
parameter of Kuang et al. (2010) that are below 0.3, further indicating the
applicability of their postulate that nucleation is favored by LΓ
values below 0.7. Based on aerosol particle composition measurements it
appears that aerosol particle formation and initial growth to approximately
30 nm diameter is dominated by ammonium and sulfate. Conservative estimates
of the percent contribution of H2SO4 to aerosol particle growth
(for sub-30 nm aerosol particles) on five A-class event days ranged from 23
to 85%. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|