doi:10.1038/nindia.2011.125 Published online 29 August 2011
Nanoparticles spewed by vehicles could spell doom for people living in metro cities such as New Delhi, according to new research. The researchers claim that ultrafine particles (less than 100 nanometre in diameter) can easily invade the lungs and blood stream of city dwellers, aggravating existing pulmonary and cardiovascular diseases.
"These nanoparticles could accelerate the mortality rate in Delhi in years to come," says lead researcher Prashant Kumar.
Vehicles remain the largest contributors to atmospheric nanoparticles. With the number of vehicles expected to grow in megacities, higher levels of nanoparticles are expected to adversely impact human health, urban visibility and global climate. Exposure to nanoparticles is linked to respiratory and cardiovascular diseases and increased rates of mortality.
A study was launched to assess the contribution of vehicles to atmospheric nanoparticles and related risks of mortality in New Delhi. The researchers estimated total particle number (ToN) concentrations and linked it to mortality under two future scenarios: business as usual (BAU) and best estimate scenario (BES). ToN shows atmospheric concentration of nanoparticles emitted by vehicles.
In the BAU scenario, no policy interventions were considered. BES considered intervention measures such as transport and emission control policies and infrastructural development for road transport. Six vehicle categories — passenger cars/jeeps, 2-wheelers, 3-wheelers, buses, light duty vehicles (LDVs) and heavy duty vehicles (HDVs) — using various kinds fuels were studied.
In recent years, Delhi's population and vehicles have swelled at an astonishing pace. From 2001 to 2006, the city's population increased by 21.5% as against a national population increase of 7.5%. The population is expected to increase further by about 54% in 2030 from 2006 levels.
The study looked at both ambient (15 m above road level) and roadside (about 2m above road level) ToN concentrations with particle size between 5-300 nm. For Delhi inhabitants, current exposure to ambient and roadside ToN concentrations is of the order of about 10,000 and 100,000 per cc respectively. About 85% of this ToN concentration, mostly in the ultrafine size range, comes from road vehicles.
The study found that annual ToN emissions is expected to increase by around 4.21 times in 2030 under the BAU scenario. "Under the BES scenario, annual ToN emissions are estimated to go down by two orders of magnitude in 2030 from the 2010 levels," says Kumar.
The researchers have found that passenger cars (taxis, cars and jeeps) are the second largest contributors (25-34%) to ToN emissions after the HDVs in all scenarios, mainly because most of them run on gasoline and diesel.
"Without any intervention, around 1,888 more deaths per million people are projected by 2030, indicating a serious need to control the nanoparticle emissions at source," Kumar adds. With mitigation measures, the death rate is expected to be around 31 per million people.
Manas Ranjan Ray of Chittaranjan National Cancer Institute, Kolkata, who studies the effects of urban air pollution on health, says the extremely small size and greater surface area of ultrafine nanoparticles help them adsorb more harmful organic chemicals than SPM. "Loaded with such harmful chemicals, they easily reach lungs and get into the blood stream. They can even reach the brain crossing the blood-brain barrier," Ray cautions.
In brain, such nanoparticles can trigger a cascade of abnormal physiological changes leading to disorders such as Parkinson's and Alzheimer's disease.
The authors of this work are from: FEPS University of Surrey and University of Birmingham, United Kingdom; Civil Engineering Department and Centre for Transportation Systems (CTRANS), Indian Institute of Technology Roorkee, Uttarakhand, India.