Today we review research into the distribution of air pollution at a higher resolution than many urban studies, looking at how it changes during the day and within neighbourhoods and between streets in New Zealand’s capital city of Auckland. Fixed air monitoring stations either close to traffic or away from it tend to miss high resolution pollution hotspots both in time and space. In this study, a specially instrumented bicycle was used to measure carbon monoxide (CO) and particulate matter (PM10) over different times of the day and for different streets in an area that was subdivided by a highway with traffic. Results indicated that while emissions from highway traffic dominated the morning rush hour, that the queued stop and go nature of street level pollution reached a peak during the mid-day and afternoon. Studies such as this need to be considered for the placement of populations whose health is at risk due to air pollution, such as early childhood centres and the elderly in retirement homes (which should be separated by at least 100 m from major roads).
Key Quotes:
“For major highways …long-term average concentrations of UFPs, nitrogen oxides (NOx) and black carbon (BC) tend to be at least 50% higher within the first 50-100 m than sites further from the highway …This results in significantly elevated long-term exposures for residents living within this zone of influence.”
“studies have reported an association between poor urban air and diabetes prevalence, exacerbation of asthma in young children and more rapid cognitive decline in the elderly.. Where possible, the placement of …early childhood centres, schools, retirement homes and social housing projects next to high-emission zones should be avoided. Some researchers are now advocating for a complete separation of at least 100 m between all residential buildings and major roads”
“mobile monitoring methods are becoming increasingly popular due to the relative low-cost and ability to capture data at high spatial resolutions.”
“diurnal change in PM10 for both areas, with some evidence of highway-traffic increasing concentrations during the morning rush hour. The mobile plots also show evidence of heavy vehicle influence at the arterial routes during the midday …and afternoon periods"
“local street traffic has a dominant influence during the day and domestic burning at night/early morning, in turn diluting the signal from the road network …CO emissions factors are in fact lower for highway traffic than for street traffic due to the highest emissions occurring under heavy acceleration, and the stop-go nature of street level driving, possibly explaining the peak events within our CO plots.”
“We have also been able to clearly illustrate the shifting spatial impact of the freeway (decreasing during the day) and the importance of arterial routes during the midday and afternoon periods….due to a combination of higher winds trapping plumes within street canyons and the direct emissions from queued stop-start traffic within the canyons themselves.”
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