Reference: Targino, Admir Créso, Patricia Krecl, João Edson Danziger Filho, Julián Felipe Segura, and Mark David Gibson. “Spatial variability of on-bicycle black carbon concentrations in the megacity of São Paulo: A pilot study.” Environmental Pollution 242 (2018): 539-543. Doi: https://doi.org/10.1016/j.envpol.2018.07.003
Traffic, Bikes, and Black Carbon
Have you ever been stuck in traffic? I already know the answer is yes. Many major cities, such as São Paulo in Brazil, are experiencing an increase in traffic and air quality problems.
Enter bicycles. Using bikes can relieve traffic congestion, decrease greenhouse gas emissions, and can be better for your overall health. However, only 1% of São Paulo commuters use a bike (compare that to the gold standard of Copenhagen, where 35% of commuters are cyclists). In order to promote bike commuting, a bicycle lane was constructed along Paulista Avenue, an 8-lane highway in São Paulo.
Now for the twist. A biker traveling along a major highway can be exposed to air pollutants, especially those from car exhaust like black carbon. Black carbon is a byproduct of fossil fuel combustion, and when inhaled, can cause negative health effects, particularly in the lungs. Thus, the main objective of this study was to look at the potential air quality impact on bike commuters, using black carbon concentrations as the indicator of fossil fuel emissions.
The Methods: Riding a bike while collecting black carbon
The study compared black carbon exposure between a quiet and busy road, so bike-riding researchers looked at black carbon concentrations from bike lanes with two different traffic rates. The first was along the traffic-heavy eight-lane Paulista Avenue, while the second was a nearby road through a quiet neighborhood. Black carbon concentrations were assessed during four weekdays and one Sunday in August 2017, to compare weekdays and weekends as well.
Bicyclists used a portable sensor called a microaethalometer to collect black carbon concentrations every 10 seconds. The microaethalometer detects the amount of radiation absorbed on the instrument’s filter, which is related to the amount of black carbon particles the biker would have encountered.
What did they find?
Black carbon concentrations along Paulista Avenue were comparable to major cities including London, Shanghai, and Bogotá. Average black carbon concentrations were 8.5 times higher along Paulista Avenue on the weekday compared to the weekend. Similarly, black carbon concentrations were tenfold higher on the weekday compared to the weekend along the residential roadside. This indicates that the exposure of a bicyclist to fossil fuel pollutants increases greatly during the normal weekday commute to work.
Interestingly, the exposure to black carbon during the weekday was only 1.6 times greater on the major Paulista Avenue compared to the nearby quiet residential road. Lastly, black carbon concentrations alongside Paulista Avenue were nearly 17 times greater if there was a traffic stop (such as a red light) compared to the normal flow of traffic.
What does this mean for a bike commuter?
Cyclists using the bike lane along Paulista Avenue during the weekday could be exposed to elevated concentrations of black carbon. Those opting to bike through a calmer neighborhood have a slight decrease to black carbon exposure since there is less traffic. This suggests that future bike lanes should consider local traffic patterns and aim to create bike lanes on secondary roadways through quieter areas – although that is not always possible.
Additionally, the drastic decrease in black carbon concentrations between the weekday and weekend demonstrate that a weekend bike ride is likely healthier from an air quality perspective, and that the residence time of black carbon is very short, meaning that black carbon does not stick around in the atmosphere for very long. This is an encouraging outlook: future reductions in traffic rates could have nearly immediate reductions of black carbon.
The final note from this study stresses that it is a pilot – that is, out of many existing air pollutants, only black carbon was measured, and the study only covered five days in a single year. However, this study can be used to inform cyclists of when and where is the best place for them to enjoy a bike ride, while also suggesting that vehicle reductions could have vast improvements on the air quality.