Tuesday 15 January 2019 and the real-time Air Quality Index (AQI) reads 168 for Bangkok. Little red flags dotted on a map of areas of the city. I’ve been curious as the sources of the air pollution. You can accept as gospel what you read online or in the press. I wanted to dig deeper into understanding the nature and danger of the main air pollutants. I decided to ask an expert with no axe to grind about understanding the causes of the pollution and assessing the relative health impact of each.
I reached out to an international expert Dr. Mark Jacobson, Professor of Civil and Environmental Engineering and Director of the Atmosphere/Energy Program at Stanford University. Jacobson’s area of expertise is environmental engineering, air pollution and global warming modelling.
Professor Jacobson wrote me, that “The only way to determine the relative impact of each of the sources listed is 3-D computer modeling of air pollution that accounts for emissions, atmospheric chemistry, deposition, meteorology, radiative transfer, and cloud processes.”
The process is to run simulation with each source (e.g., dust, smoke from outdoor fires, vehicle exhausts, weather conditions) removed and this would establish a series of benchmarks based on any one particular source, which is causing the greatest impact. Professor said “Such modeling is actually required by law in the U.S. under the Clean Air Act Amendments of 1990 in, for example, ozone non-attainment regions. There are plenty of consulting companies that do this kind of work (AER, Environ, SAI, Sonoma Technology, Tetra Tech, to name a few in the California alone).”
Not all of sources of pollutions are equal in the damage done to human beings. Professor Jacobson observed, “that vehicle exhaust will cause the greatest damage because the human intake fraction of vehicle exhaust air is much greater than the intake fraction of pollution from a source far away. People are literally breathing in the exhaust. The other sources are more dilute.”
The PM2.5 or fine particulate matter with a diameter of less than 2.5 micrometers should be less than 50 micrograms per cubic metres. The Bangkok Post reports “The PM2.5 measured 60-81mcg on the streets and 49-79mcg away from main roads.”
The best choice may be an unpopular one. We may have no choice, if supported by test results, to impose restriction on the use of cars, motorcycles, buses, vans, and trucks. The immediate question is whether vehicle exhaust air has become a public health hazard setting up long-term adverse health consequences to the population breathing the polluted air. What is weighed in this equation: The cost of disrupting transportation system or diminishing the health of the resident population to preserve the economic infrastructure. In the future, we can expect to frequently confront the public policy dilemma between choosing between economic growth and public health.