permaculture

[rmhoward@omninet.net.au]

On 18 Sep 2003 at 8:31, Gilbert Grace wrote:
> 
> "...I do not know if I would be prepared to drink rainwater falling on
> Sydney roofs, however. A look at airflow map for the Sydney region
> indicates that polluted air is pushed out to sea, depending on winds,
> and can then return and settle south-west of the metropolitan area.
> That puts it over the Campbelltown-Camden region, where the
> inhabitants get to sample three-day old city air. Whether this air is
> so polluted that it could contaminate rainwater, even to a small
> amount, is unknown. Clearly, what we need is the testing of rainwater
> in different regions of Sydney over the different months.Perhaps one
> of those first-flush diverters that channel the first rainwater wash
> over the roof into the stormwater drain would be a good idea.
> 

In Perth there is a distinct daily sea breeze which occurs in summer. In the 
morning, 
summer easterlies take pollution out over the sea and this pollution is 
bought back on 
the sea breeze in the afternoon. Air studies in Perth in the 1980's 
established that 
there was a hlaf hour daily spike in pollution levels as the sea breeze came 
in with 
pollution levels rising to up to 10 times the average daily level.

In Sydney the situation is somewhat different since there is no distinct sea 
breeze. 
However, the Perth measurements do indicate that, when the winds turn due to 
diurnal 
effects( ie a sea breeze) or because of meteorological conditions i.e. a 
change in the 
weather, then the maximum period of pollution is at the time of the wind 
change. 

If the wind change is associated with rainfall then first flush diverters 
will also work as 
pollution revention agents. taking the most polluted water with them. 
(Assuming where 
talking about NOx, SO2 and similar water soluble pollutants and dust).   

Bob howard