UP weather expert: ‘Stagnant air’ traps local pollution
Was Metro Cebu covered for a while in forest fire-stoked haze or urban smog?
Both, according to Dr. Gerry Bagtasa, an atmospheric physicist with the Institute of Environmental Science & Meteorology, University of the Philippines (Diliman).
The Manila-based weather expert said the reduced visibility in Metro Cebu in recent days was a combination of haze from Indonesia and local pollution trapped by “stagnant air”.
He posted his analysis on his weather forecast website weather-manila.com to explain “the recent Cebu haze” experienced in the morning of Oct. 1.
“It’s BOTH from Indonesia and an effect of tropical storm KabayanPH(Mujigae) on local pollution emission,” said Bagtasa. He posted four maps showing changing wind directions in the Philippines and a series of satellite images showing “movement of smoke from parts of Indonesia.”
During the southwest monsoon, there is a “wind funneling effect” along Tañon and Cebu Straits where these relatively strong winds disperse pollutant emissions in Metro Cebu, he said.
However, on Oct 1. when Tropical Storm Kabayan was northeast of Visayas, wind speeds in Central Visayas slowed down as northerly to northwesterly wind in north Visayas ran counter to prevailing winds from the south.
“This slowed wind plus the complex interaction of mountains, land and water lead to stagnant air around Metro Cebu,” he said.
One map showing an orange mark over Metro Cebu in the east coast “is simulated NO2 (nitrous oxide) gas which is an air pollutant that mainly comes from cars/ gasoline use,” he said.
Why was only Cebu affected?
Bagtasa linked this to Cebu’s profile as a “large city with comparatively higher emissions.” Cebu is the second biggest metropolis in the country after Metro Manila, with a dense population of people and motor vehicle traffic.
Days before Oct. 1, when Kabayan was still a Low Pressure Area, there was “stagnant air in the region,” said Bagtasa. This resulted from “winds of opposing direction moving toward each other.”
The LPA created a northerly wind around Central Visayas while the prevailing wind was from the south, he said.
Media reports of “haze” in Cebu emerged on Oct. 1 after unusually gloomy skies and fog were observed with cooler temperatures since September 26, a Saturday.
The Mactan station of the state-run weather bureau Pagasa said visibility went down from a distance of 10 kilometers to 7 kilometers. The weather station had to give hour-by-hour updates to aviation authorities in the Mactan aiport.
The Environment Management Bureau (EMB) 7 advised the public to stay indoors or wear protective gear like a face mask or goggles until they did air quality tests.
Results released yesterday by Engr. William Cuñado, OIC, said sampling conducted on October 1 and 2 shows that air quality “ranges from fair to good.”
The samples were taken in five stations in Cebu Business Park, Mabolo, the DENR 7 office in Sudlon, and Beverly Hills, all in Cebu City, and a station in Naga City.
“Our air quality station in EMB Central Office in Manila says that until now, they have not detected a haze episode,” said DENR 7 spokesman Eddie Llamedo.
The skies in Cebu significantly cleared up by October 5.
After October 1, said Dr. Bagtasa in his post on Sunday, “currently there is a strong northeast wind partly affected by STS (severe tropical storm) Choi-Wan while typhoon Mujigae is creating a southerly wind in West PH sea, inducing wind shear across Central Visayas.”
The UP associate professor stood pat on his opinion that biomass burning in Indonesia was part of the cause of the haze.
In reviewing satellite photos, he said Sept. 22 to 23 showed gaps in clouds over Visayas and that “due to the location of Dujuan and its slow NW movement, it created a pathway for a couple of days for the haze to reach parts of PH.”
While most parts of southern Philippines “were covered by this relatively thin haze”, reduced visibility was worsened by local pollution emissions mainly in Metro Cebu and at one brief period in Bacolod.
Bagtasa received his doctorate degree in the field of atmospheric physics in Chiba University in Japan. His website was developed as a supplement to the PAGASA forecast.
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