Provide adequate street cleaning

That's how you do it

Street cleaning, especially sweeping and then spraying, helps to temporarily lower the concentrations of particulate matter (PM ₁₀ ) along the side of the road. You see the greatest effect when the cleaning is done just before rush hour. However, the effect on the daily mean concentrations is limited. Moreover, street cleaning has no influence on gaseous pollution (eg NO ₂ ) and probably little effect on finer dust (PM _2.5 ). The limited amount of evidence shows that the impact mainly depends on local conditions such as for example the weather or the condition of the road surface.

These are the observed effects on the main pollutants according to scientific studies:

• Particulate matter (PM): the effect is difficult to determine due to conflicting results. It seems that a combination of rinsing and wiping gives the best outcome, with a maximum decrease of 10% for PM ₁₀ .
• Soot (EC): the effect is unknown.
• Other pollutants: there are no effects for O ₃ , NO ₂ or volatile organic compounds (VOC).

Additional benefits of this measure:

• Sand or mud is removed from roadways.
• There is less waste on the streets.

Can street cleaning solve your local air quality problem? Proceed as follows:

1. Are there complaints about dust deposits on, for example, windows, window sills or drying laundry? Model maps are less suitable for monitoring these effects: the problem is sometimes very local and difficult to predict. Measurements of the coarser dust particles often give an indication.
2. What are the possible sources of pollution in the immediate vicinity? If blowing dust from a street is the most likely source, then definitely consider this measure. If the blown up soil dust comes from, for example, an agricultural area or industrial activities, then other measures are more efficient. Think of green barriers or operational measures in the adjacent areas.
3. If necessary, monitor the impact of street cleaning by measuring for a period of time. For this you can go to provincial environmental labs such as the Provincial Institute for Hygiene or the Provincial Center for Environmental Research.

Knowing more

Study on mechanical sweeping, supplemented with vacuuming

Barcelona, Spain - 2010

For a week, the researchers tested how effective street cleaning is. The test took place at night between 11 p.m. and 2 a.m. on Avenida Valencia, where a mechanical sweeping vehicle with a vacuum cleaner cleaned a 1.2-kilometre strip. The road surface was then manually sprayed with groundwater. On the sidewalks, the researchers briefly registered 6% less _PM10 (between noon and 6 p.m.). However, the effect on the total daily _PM10 concentrations did not materialize, probably due to the strong influence of the weather conditions and their impact on the daily concentrations. The decrease in _PM10 concentrations in the afternoon was associated with a decrease in the particulate matter components: for the coarse particles, a 10% decrease was observed in the brake wear elements and a decrease of 12 to 28% in the mineral particles (Si, Al, Ca, Ti, Sr). In the fines, the mineral particles decreased by 7 to 16%.

Study on mechanical sweeping, supplemented with vacuuming and spraying

Madrid, Spain - 2011-2012

For a week, a mechanical sweeping vehicle sucked up the coarse, precipitated particles at 3 test locations every day. Around 11 p.m., the road surface was sprayed with water under high pressure.

If the streets were not hosed, the PM10 content was 2 to 15% higher than when they were hosed at night. However, there is a lot of uncertainty about these results. Indeed, continuous measurements of the _PM10 concentration showed that the observed decrease was short-lived (from 3 to 5 a.m.). The hourly concentrations of PM _2.5 were not affected by the street cleaning.

Study on dust suppressants and different street cleaning techniques

London, UK - 2013

Transport for London has extensively tested the effectiveness of dust suppressants in reducing local _PM10 concentrations. On _PM10 hotspots, the researchers tested different methods that are more intensive than the usual street cleaning techniques.

Dust control appeared to have an effect on _PM10 concentrations at industrial and construction sites. These are places where the pollution is traditionally exceptionally high and where large areas could be treated. On roadways, however, there was (almost) no effect in terms of PM ₁₀ . In other words, it was not possible to demonstrate that intensive street cleaning improves air quality.

Research based on local data

Nevada & California, USA

In Lake Tahoe Basin, the effectiveness of dust control measures such as street sweeping was investigated. A mobile test platform was used to collect dust emission data in the margins of a broader study into road maintenance for a year.

This research was carried out over a large area and over a long period of time. The results showed that street sweeping is effective in controlling dust emissions on roadways. A combination of spraying and sweeping cleans better and is therefore more effective. According to this study, street cleaning may have a positive effect on the concentrations of particulate matter and no effect on gaseous pollution (such as NO ₂ , O ₃ and VOC). Because the dust residues build up quickly after cleaning, street cleaning is only effective for a few hours.

More information

• A scientific review discussing several worldwide studies on street cleaning and air pollution effects: A review on the effectiveness of street sweeping, washing and dust suppressants as urban PM control methods.
• An extremely interesting overview with various examples of street cleaning as a mitigating measure can be found in: The scientific basis of street cleaning activities as road dust mitigation measure , AIRUSE project .