Many
of us would like to sample green living in urban canyons rather than suffer the
dull grey, hot polluted atmosphere in many of our crowded cities. Big open
squares and green parks help, but we have to plod between these oases in the
urban desert.
Pugh
et al hit on a solution and have published it in Environmental Science
& Technology (1,2). They propose that the walls, and possibly roofs, should
be planted up and down. The greenery can act as a filter for the NOX’s and all
those particulates that our diesel engines are spewing out.
Tough
evergreens that are drought resistant would be best, so ivy is a good candidate
and climbing walls would have to be provided if sufficient height is to be
safely attained. Tree lined streets can help a little, but they can also trap
the noxious nasties down at street level.
The
authors set up computer models of airflow in street canyons and showed that
cross flows produce air circulation within the canyons. Aligned canyons, of
course will have plenty of flow down them. Deep well-covered canyons should
work well. For example a fully covered green canyon twice as high as it is deep
could clean out 45% of the dirty diesel particulates. The paper suggests that 40%
of NOX’s and 60% of particulates could be attainable.
Green
living in urban canyons would have other fun benefits with birds having a huge
increase in free real estate for raising their families. The insect life would
be in constant supply so we’d all win.
- http://pubs.acs.org/doi/abs/10.1021/es300826w
- http://www.bbc.co.uk/news/science-environment-18873391
