Dust scattered in the air or fugitive dust raise public health concerns. Therefore, Seoul is launching a dust cleaning project to protect citizens’ health and to keep urban life clean and dust-free.
 

Ultrafine Particles Mostly from Road Dust
Dust scatter due to vehicles on the road or from construction activities. Scattered dust on the road takes up 62% of all ultrafine particles (PM-2.5), of which 48% are fine dust (PM-10), 12% ultrafine particles (PM-2.5). Seoul is connected through 8,148km of roads, and considering several lanes of each road, about 24,252km will need to undergo dust cleaning. In 2014, Seoul completed the cleaning project for a total of 1.2 million km of road, of which 950,000 km was done with water cleaning and the remaining 25km with regular dust cleaning.
 
Dust Cleaning on the Road
Constantly occupied by men and vehicles, roads are inherently filled with various types of dust such as car fumes, worn-out materials from car tires and brakes, and spring yellow dust. The harmful dust scatters around as vehicles run off the road, polluting the air and threatening the health of citizens.
To tackle this problem, Seoul began the road dust cleaning project since 2007. Under the project, the city government provided its 25 administrative districts with washing equipment and devices to such as road washing vehicles and dust absorbing devices. To date, Seoul’s 24,525 km of road including main roads in Seoul, backside roads, alleys and pedestrian streets were cleaned of dust several times, making the cumulative sweep coverage more than 7 million km.
 
From Water Washing to Dust Absorbing
Seoul is in the process of switching its cleaning method from water washing to dust absorbing. The latter is said to absorb 98.2% of ultrafine particles and 98.3% of find dust, without having to use water at all. Seoul will secure 70 of the dust absorbers by 2018 and further enhance efficiency of the cleaning project overall.

More Systematic and Effective Road Cleaning
Road cleaning is conducted daily for over 6-lane arterial roads (947km), every other day for road with 2-4 lanes (861km), weekly for less-than- 2-lane roads such as backside roads (6,340lm). The cleaning team follows a systematic approach with effective role allocation; the road surface cleaning vehicle stands in the front, cleaning both sides of road, followed by dust cleaning vehicle that stands next to the center lane ready to absorb dust scattered from the vehicle ahead of it. At the very back of the fleet comes the water spraying vehicle to clean up everything left behind.
To minimize inconvenience to citizens, cleaning is conducted at night or early in the morning (mostly from 11pm to 7am) when traffic flow is lowest and atmosphere is stable. To get the work done fast, all available vehicles are deployed during these hours. Water conservation is an important principle underlying the dustcleaning project. Therefore, instead of using water from waterworks, wastewater such as effluent or runoff from water reuse centers or subways are used for cleaning. A pedestrian street cleaning is equally important. Each administrative district takes care of cleaning roads in their jurisdiction and dispatches a dedicated team for washing sidewalk, popular tourist area, trash dumper, and cleaning street facilities.
 
Enhancing Efficiency of Water Spraying
To secure stable supply of water for cleaning, various types of hydrants besides underground water is used. Thanks to the active mobilization Seoul experienced far less lack of water source and wait time while substantially reducing the distance required to get to the water source. Such effort led to a 3.1 times higher efficiency than before.
 
Cleaning Fleet Management System
Seoul created a cleaning fleet management system by installing GPS, GIS to road dust cleaning vehicles. The scientific and systematic system allows the city government and all of its administrative districts to track the status of all vehicles under their management.
 

High Public Satisfaction
A survey on Seoul’s road cleaning project showed that 83.4% of the respondents found the sanitary level of roads to be satisfactory, and 90.9% answered that water washing road indeed contributes to cleaner roads.
 
Reduced Road Dust
A particle size analysis was conducted to closely look into the number and volume of particle as well as optimal concentration level. Designed to evaluate the effectiveness of road dust cleaning project, the analysis concluded that water spraying reduced the optical concentration from 3.2% to 0.6%, demonstrating that all types of particles are reduced after water washing. This clearly shows that road water washing reduces road dust to a great extent.
 
Road Cleaning Fleet in Operation Year-round
Water washing has it limits as it cannot be done in wintertime. As an alternative, road dust cleaning fleets that do away with water yet absorbs 98% of ultrafine particles and fine dust will be used more extensively. The alternative approach will ensure year-round cleaning, help conserve water and reduce inconvenience to citizens such as water splash.