 |
| Titel |
Radon-222, a proxy for vertical mixing of emissions in the urban nocturnal boundary layer |
| VerfasserIn |
S. Chambers, A. G. Williams, A. Griffiths, J. Crawford, W. Zahorowski |
| Konferenz |
EGU General Assembly 2012
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250060561
|
|
|
|
|
|
| Zusammenfassung |
| There has been growing concern in recent decades regarding the health implications of
fine particles (-¤ 2.5μm), which are readily deposited deep within the lungs. In
the interests of public health, and improving the predictive ability of Chemical
Transport Models, it is imperative to improve our understanding of the diurnal
variability of primary pollutant and precursor concentrations by, among others,
improving our understanding of the underlying physics of transport and mixing
processes. From the time of their release until they are removed from the atmosphere,
the level of public exposure to emissions is closely related to rates of near-surface
horizontal and vertical dispersion, the depth of the atmospheric boundary layer,
and the venting from the boundary layer. These parameters, in turn, are dependent
upon the amount and nature of mixing, which is closely related to atmospheric
stability.
With the exception of bushfires and dust storms, the greatest risk of public exposure to
emissions occurs under “inversion” conditions, when the atmosphere is stably stratified.
These very conditions are notoriously the most problematic for contemporary weather and
chemical transport models. At such times the structure of the lowest 10-100m of the
atmosphere can be quite complex, potentially containing multiple disconnected
layers, and even stability measures based on surface similarity theory can fail (or
yield inconclusive results) without sufficient vertical and temporal measurement
resolution.
Near-surface radon measurements provide a direct measure of the degree of dilution of
surface-emitted scalar quantities by vertical mixing at night that is completely independent of
local meteorological measurements and does not fail under conditions of near calm, which
occur on the most stable nights. As such, they are a valuable proxy for potential pollution
accumulation. In this study we analyse and discuss 22 months of continuous hourly
observations within an urban airshed south of Sydney, Australia, that is affected by a
heterogeneous distribution of emission sources. We develop a simple method for
characterising and quantifying the strength of atmospheric mixing at night over land, and
demonstrate the usefulness of this radon-based technique over and above conventional
stability classification measures in identifying atmospheric conditions conducive to the
accumulation of significant pollution in the lower atmosphere. Our findings show that at
spatial scales comparable to those of a large city, continuous radon observations from a
single, economical, low-maintenance detector can provide a clearer indication of potential
pollution levels than conventional metorological measurements. Furthermore, despite
significant industrial, urban and rural emissions within the airshed, we show that the highest
hourly rates of public exposure to PM2.5 aerosols in the Wollongong city centre under
strongly stable conditions are due to domestic wood smoke emissions from the western
foothills. |
|
|
|
|
|
|