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6 Apr 2016 | Atmosphere Initiative

Reducing Pollution from Motorcycles

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The air in Kathmandu is extremely polluted, with fine particles (PM2.5) being the major cause of concern.  If you ask the average resident where all the pollution is coming from, many will point the blame at vehicles. But when we look for ways to reduce vehicular emissions, the barriers seem insurmountable.  Poor road conditions, adulterated fuel, unqualified maintenance workers, and a faulty emissions inspection program are just a few of the explanations offered for the smoke-belching fleet of vehicles in the valley. This dismal situation was illuminated by a glimmer of hope during the Nepal Air Monitoring and Source Testing Experiment (NAMaSTE) in April 2015, when exhaust measurements from 5 idling motorcycles suggested that routine maintenance might reduce the PM2.5 emissions from 2-wheelers by a substantial amount.

To explore this prospect further, ICIMOD started an intensive measurement campaign in December at local motorcycle workshops. Using low-cost, hand-held instruments, we measured gaseous and particulate pollutants in the exhaust of each bike that was brought to the workshop for servicing. We then repeated the same measurements after the bike received an oil change, carburettor check, and cleaning of its air filter.  After sampling the exhaust from 30 motorbikes, we noticed a trend.  Most of the vehicles were emitting undetectable amounts of PM2.5 when they arrived at the workshop, so the service could not possibly reduce their emissions. However, a few of the motorbikes were emitting visible plumes of white smoke upon arrival. After receiving routine maintenance, PM2.5 could no longer be detected in the exhaust of those motorbikes.  This realisation prompted a second phase of our study that started in February.


Along with graduate researchers from theTribhuwan University Central Department of Environmental Sciences (TU-CDES), we stood at a busy roadside and stopped vehicles that we could see were emitting a lot of visible smoke. We offered to the drivers of these high-emitting vehicles a free maintenance service (cost ≈ NPR 1000) if they would agree to be part of our study. We then proceeded to measure the motorbike emissions before and after servicing in the same manner as the first phase of our study. The preliminary results are very promising. After the routine service, PM2.5 from most of the high-emitting vehicles were reduced substantially. In many cases, the gaseous emissions of volatile organic compounds (VOC) and carbon monoxide (CO) were greatly reduced as well.

The TU-CDES students classified approximately 1% of the on-road fleet as high-emitting. That tiny fraction of the vehicle population is contributing a disproportionately large share of the total PM2.5 emissions from Kathmandu motorbikes. Overall, 2-wheelers account for 80% of the vehicle fleet in Kathmandu and current regulations do not require an emissions inspection test for this class of vehicles. If a policy can be designed that requires high-emitting motorcycles to go for routine servicing at a local workshop, the total vehicular emissions could be reduced greatly.

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