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No doubt, a lot of Metro Manila’s denizens have noticed the seemingly clearer air surrounding the megacity, and have been snapping up pictures of a city skyline showing clearer resolutions compared to those taken before the imposition of the government’s enhanced community quarantine (ECQ) in mid-March that forced most private motorists to stay at home and all public transport to be suspended.

Surely, the absence of most vehicles on the road (especially those smoke-belching public utility buses and jeeps) has something to do with this, mirroring a similar observation in continental Europe. The Weather Channel TV network @Pattrn remarks: “The strong drop in pollution across Italy, Spain and France amid the #COVID19 lockdown is visible in @esa data from the Copernicus Sentinel-5P satellite. The drop in nitrogen dioxide concentrations coincides with the strict quarantine measures in each country.”

But does the absence of vehicles necessarily translate to cleaner air? Peter DeCarlo, an expert in atmospheric air pollution and an associate professor in the Department of Environmental Health and Engineering at Johns Hopkins was interviewed by Hub (a Johns Hopkins news center), and he explained that there were other things to consider in measuring air pollution. He said pollutant concentrations are strongly governed by meteorology—how winds move things around, how sunny it is, and if it’s raining or not.

Air quality sensor at Mendiola (Photo courtesy of Clean Air Asia)

He said that there may be fewer cars on the road, and we’re indeed seeing the effect of decreased emissions, but if more people are lighting fires in their homes, then that’s going to offset some of those gains.

He also mentioned that air pollution is much more than what the naked eye can see. One of the most harmful pollutants is PM2.5, or particulate matter smaller than 2.5 microns in diameter. By comparison, DeCarlo pointed out that the diameter of a single strand of hair is about 80-100 microns. Thus PM2.5 can easily be inhaled into the lungs, and in sufficient quantities, can be harmful or fatal.

Thus, we may be in awe of the perfectly clear air in the city, but how much of the invisible PM2.5 is actually swirling in there?

Inquirer Motoring tried to reach the Environmental Management Bureau-Air Quality Management Section, but as of presstime the agency—which manages the air quality monitoring for the entire country—had not replied.

Dang Espita-Casanova, Program Lead of the Air Quality and Climate Change Program of Clean Air Asia, told Inquirer Motoring, “Overall, we can’t influence how people would perceive changes in the environment except for when we are able to provide thorough and validated data and information. What is important is that the ECQ demonstrates that clean air is indeed achievable if measures are in place to control emissions even after the ECQ.”

The Clean Air Asia team, along with the 3M company, has partnered with the city government of Manila on a project that monitors the average PM2.5 levels at three sites in the city. The air quality monitor at Freedom Park at the Manila City Hall showed a 42-percent drop in PM2.5 levels during the period April 13 to 17 compared to measurements during the regular work/school weekdays pre-ECQ (January 21 to March 6).

Rizal Park’s air quality sensor installed (Photo courtesy of Clean Air Asia)

That contrasts, however, with the PM2.5 readings at the two other sites. The sensors installed at Rizal Park in Ermita for the same period showed that average PM2.5 level was 2 percent higher compared to pre-ECQ levels. In the Mendiola site, sensors registered PM2.5 levels higher by 9 percent compared to pre-ECQ readings.

The Unioil petroleum company may offer a partial explanation for this discrepancy. Unioil currently operates Air Visual quality monitors at 36 of its stations. “Metro Manila readings have improved because of the ECQ. Right now, we’ve been mostly in the green zone. However, we can see air quality during ECQ is worse in the mornings, which could be linked to people going out with cars to get their essentials,” the social media page of Unioil explained to Inquirer Motoring.

Clean Air Asia’s three air quality sensors in Manila City operate under the Asia Blue Skies Program. CAA has been in close coordination with the Manila Department of Public Services and the Manila Public Information Office.

Casanova disclosed that the data coming from the three sites are greatly influenced by, among others: (1) Pollution sources or the activities that happened/are happening in the vicinity of the sensor sites, which may include vehicular movement, public activities, fires, and others; (2) Geography, and;  (3) Local meteorological parameters such as wind speed, wind direction, and relative humidity, among others. These factors lead to either increases or decreases in the quality of air (in this context, with PM2.5 as a determinant) in these areas.

Asked if substantial vehicle reductions had something to do with the drop in PM2.5 levels at the Freedom Park area (which is situated by the road), and the specific factors that could have caused PM2.5 readings to increase in Rizal Park (which was in the middle of greens) and in Mendiola (within the university and residential areas), Casanova replied, “Due to mobility restrictions, the Manila Department of Public Services has not been able to deploy personnel to do ‘ground-truthing’ in the sites during the period of increased levels. Matching data that is coming from the sensors with on-the-ground observation of activity is one of the means to validate and further explain the data. We continue to work with DPS and the Hinga Maynila Task Force to gather as much information as we can to explain this.”

Casanova told Inquirer Motoring in an earlier interview that air quality would, indeed, be influenced by activities within the vicinity of the sensor. Understanding the characteristics of the sites and the possible activities that can be conducted within the area would explain these differences. She also added that her team has also been working with Pag-Asa to look into meteorological patterns relevant to Manila City.

From fossil fuels to lungs

Casanova explained that PM2.5 is just one of the many types of air pollutants, and a by-product of combustion processes, which include burning of fossil fuels in industries, emissions from transport, and biomass burning. Particulate matter can also be vehicles for other toxic substances such as heavy metals.

“PM2.5 can penetrate deep into the lungs and enter the bloodstream, which causes different health impacts. This is also the reason why PM2.5 is most often used as an indicator of air quality,” said Casanova.

Meanwhile, in San Juan City, car enthusiast and motoring scribe Leslie Sy has also been measuring air quality in his area by using three PM2.5 monitors—two installed at the ground and 12th floors of his condominium, and the third a handheld portable unit. The Chinese-made monitors, he attests, are reliable.

San Juan has been registering a consistent “good” range since the ECQ began, Sy disclosed. “The readings have been between ‘clean’ and ‘cleaner’ of the ‘good’ range of the PM2.5 scale. Current PM2.5 reading is 1. The typical ECQ readings have been between 1 and 15. The normal pre-ECQ readings would display between 1 and 30, peaking at 40 to even 50 during lunch and dinner.”

Sy concluded: “The air quality in San Juan City is generally quite clean.”

MAIN PHOTO shows a multi-sectoral group installing air quality sensors at Freedom Triangle (Photo courtesy of Clean Air Asia)