Shades of gray: Haze in Metro Manila

MANILA, Philippines – Almost every morning, Metro Manila looks like it’s under the curse of dementors from the Harry Potter series: a thick blanket of gray haze – sometimes in darker shades – envelops the cityscape, threatening to swallow the metropolis.

While the government’s air quality monitoring sites have been reporting “Good” to “Fair” status from its 12 stations, an experimental station at the University of the Philippines (UP) Diliman recorded at least two haze events since the start of 2015.

The Atmospheric Physics Laboratory of the UP Institute for Environmental Science and Meteorology (UP-IESM) headed by Dr Gerry Bagtasa recorded haze episodes at noon of January 29, and in the morning of March 14. 

The science of air pollution

Haze episodes happen when fine particles suspended in the air obscure light. Scientists said that the haze seen enveloping Metro Manila can also be called smog, or the combination of smoke and fog, indicating the presence of pollution in the air.

Dr Ronald Macatangay, head of the Climate and Atmospheric Radiation (CARBON) laboratory at UP-IESM, explained in an interview that air pollution is a combination of various gases such as sulfur oxides, nitrogen oxides, carbon monoxide, surface ozone (which is also the main component of smog), as well as particulates and volatile organic compounds (VOCs), among others.

Sulfur oxides, especially sulfur dioxide, come from burning coal and petroleum. Nitrogen oxides are produced during high-temperature combustion. Carbon monoxide comes mainly from the exhaust of vehicles, and from burning coal, wood, and natural gas.

Meanwhile, ozone could be either good or bad, depending on its location in the atmosphere, said Macatangay. The ozone layer that we know is the “good” ozone, as it traps ultraviolet radiation from the sun; on the other hand, surface ozone, or the ones produced by VOCs and nitrogen oxides and is found in the much lower portion of the atmosphere, is “bad.”

Measuring air quality

Air quality is usually measured using Particulate Matter (PM) and Total Suspended Particulates (TSP) as indicators.

The Department of Environment and Natural Resources (DENR) monitors PM2.5, PM10 and TSP.

PM2.5, particles smaller than 2 micrometers, are the most dangerous type of pollutant particles. They are small enough to enter the bronchial tubes of the lungs which could lead to severe respiratory diseases, said Tess Peralta, an engineer at the Environmental Management Bureau of DENR, in an earlier report.

PM10, are smaller than 10 micrometers and slightly larger than PM2.5, and can also be inhaled. It is small enough to settle in the bronchial tubes and the lungs, and could also lead to respiratory infections.

Meanwhile, TSP are bigger than 10 micrometers and could also be inhaled. These are the dirt that usually settles in the nostrils.

Haze episodes

The UP-IESM Atmospheric Laboratory recorded a surge in PM2.5 in UP Diliman around noon January 29, while its CARBON Laboratory saw a sudden increase in local carbon dioxide levels.

Their reports said sea breeze pushed the air along coasts inland and produced a westerly wind over Metro Manila. This wind opposed the prevailing amihan (northeast monsoon) at the same time, which led to the stagnation of air; this helped accumulate local emissions in the area.

Another haze episode was recorded Saturday morning, March 14. Bagtasa said on the Weather Manila page on Facebook that it was due to a phenomenon called “inversion,” where a layer of warm air overlaps an area of cold air. This causes the temperature to increase in the higher elevations and causes the accumulation of vehicular emissions brought by Friday night traffic.

Inversion usually happens early in the morning, said Bagtasa in an interview.

However, their data deviated from that of DENR-EMB’s mainly because of two factors: the IESM laboratories compute the air quality based on an hourly averaging system, while the DENR-EMB computes the average for every 24 hours.

In addition, the DENR-EMB’s equipment are very high-precision types, while Bagtasa’s equipment was assembled out of low-cost materials and was established for experimentation purposes.

Manila Observatory Air Quality Division head Dr James Simpas said in a separate interview that depending on the location where the monitoring equipment is located, measurements could also differ. When the equipment is on the roadside, the measurement is higher, Simpas said.

Effects of air pollution

Yet, while government data show that the air quality within Metro Manila remains safe, prolonged exposure even to smaller quantities of pollution could still harm people’s health. Among the adverse effects of air pollution are cardiovascular and respiratory diseases, and even cancer.

Other than health implications, air pollution also affects the weather, said Macatangay.

“Pollution in the atmosphere can delay rain, affect rainfall amount, and atmospheric stability,” said Macatangay.

Bagtasa explained further, “Nade-delay ang ulan to later in the afternoon, nagiging mas malakas.” (Rain gets delayed to later in the afternoon, and becomes stronger.)

In some areas, the type of precipitation, such as snow or hail, could also be affected.

Haze is more common during the dry season (December to May) as the land has lower moisture content which could lead to more dust present in the atmosphere.

Simpas said that during the dry season, the lowest possible emissions and therefore highest air quality could be measured during Good Friday and during Manny Pacquaio’s fights. Records from these days could be used as the baseline data on air quality in Metro Manila.

MACE 2015

Bagtasa also said that Filipinos have a quite low “perception of threat” of air pollution and that the correlation of air quality to weather forecasting is not explored as much.

Simpas and Bagtasa are among the scientists who are part of the Manila Aerosol Characterization Experiment (MACE 2015), a collaborative study to be conducted by the Leibniz Institute for Tropospheric Research (TROPOS) based in Leipzig, Germany, UP-IESM, the Manila Observatory, De La Salle University, and the Philippine Nuclear Research Institute.

The study, which is set to run from March to May 2015, intends to measure vehicular emissions and find how it contributes to air pollution. Measurements will be done along Katipunan and Taft avenues.

In an earlier report, DENR-EMB said that around 80% of the dirty air in Metro Manila comes from motor vehicle emissions while the remaining 20% comes from stationary sources like construction sites and industries. – Rappler.com