Ninety percent road transport relies on fossil fuel, the burning of which produces 23% of global CO2 and 19% of global black carbon. These emissions are the by-products of incomplete combustion of the motor fuels.
Despite the decline in air pollutants arising from rigorous control measures, the International Council on Clean Transport (ICCT) reported in March 2019 that transportation sector was responsible for 11% of the 3.4m premature deaths annually attributed to PM2.5 pollution from traffic.
This air pollution also resulted in 7.8m year of life lost and approximately $1 trillion (2015 US$) in health damages globally. As the vehicle population doubles by 2040 with greater traffic congestions in crowded cities, it is expected that the premature deaths would more than double.
Black carbon (BC) has recently emerged as a major contributor to global climate change, second only to CO2. BC particles have warming effect many times more powerful than CO2. It strongly absorbs sunlight and heats the atmosphere. When BC falls on snow and ice, it reduces the reflectivity and speeds up melting.
BC is a major component of PM 2.5, and is also associated with serious health problems, including respiratory, cardiovascular, cerebrovascular diseases, and cancer.
The trend towards using turbo charging and direct injection to achieve high level of turbulent mixing of fuel and oxidants in advanced engines to reduce CO2 emissions are prone to form nanoparticles and not soot.
Studies in recent years by European environmental scientists revealed that nano-sized particles are the deadliest forms of air pollution posing greater risk to health than PM 2.5. The ultrafine particles range from 6 nm – 20 µm. They are odourless and invisible, but able to penetrate deep into the lungs and blood streams unfiltered.
In the latest research, scientists in Belgium found evidence of nanoparticles in urine. This means that the tiny particles enter into the blood circulation and can go into every organ. Indeed, the same scientists also discovered that the telomeres of babies born from mothers living near the main road were 14% shorter than whose mothers lived further than 250m away from the main road.
Doctors in Mexico city have documented that airborne-rich, strongly magnetic combustion-derived nanoparticles are present in young urbanites’ brains and in neurons, glia, choroid plexus, and neurovascular units. CDNPs are associated with pathology in mitochondria, endoplasmic reticulum (ER), mitochondria-ER contacts (MERCs), axons,and dendrites.
Researchers believe that there is no safe level of nanoparticle inhalation. Alarmingly, these nanoparticles also escape the entrapment of the particulate filters installed in vehicles as required by law.
In essence, particulate mass is not a proper measure of the health hazard, because one particle of 10 µm diameters has approximately the same mass as 1 million particles of 100 nm diameters, but is much less hazardous, as it unlikely to enter the alveoli.
Nanoparticles are ubiquitous in the atmosphere. One of their key characteristics is that they possess very little mass, but are many in number. And it is for this reason that the current worldwide, mass–based, ambient air quality regulations for PM2.5 are ineffective in dealing with nanoparticle concentrations in cities.
Realising this shortfall, the European regulators are now proposing the measurement of Particle Number (PN) to limit the nanoparticle emissions in the new Euro 6d vehicles models starting from Jan 2020.
However, such legislation is inadequate as it does not include the current of 1.3 billion vehicles in use worldwide. If the issue of combustion detergency in engines is not resolved, it will also give rise to the concern that 6d compliant vehicles in 2020 may live up to expectations in reducing PN emissions under the real-world driving.