At 1,500 meters above sea level, the air changes. The fog moves in through the pine trees, and the cold bites the skin. This is Baguio, the Philippines’ summer capital, the city that has sold itself on the promise of clean mountain air.
More than a million tourists make the climb every year to escape the heat and the smog of the lowlands. What many do not know is that the air waiting for them could be as dangerous—if not more dangerous—than the one they left behind.
For Baguio is, at times, possibly the Philippines’ most polluted city.
Nathaniel Pepin, 32, has been driving jeepneys through these winding roads for nearly a decade. He remembers when the city smelled like its postcards.
“Dati talaga naamoy mo ‘yung pine tree. Pero ngayon, hindi na. Halos usok na talaga ‘yung naaamoy. (Before, you could really smell the pine trees. Now you can’t. What you smell is exhaust),” Pepin said.
For eight to twelve hours a day, Pepin and 2,000 other jeepney drivers navigate the northern Philippine city that is slowly losing its ability to breathe.
The city government knows this, but tourism is among Baguio’s key economic drivers.
When tourism hit an all-time low after pandemic lockdowns, the city launched a tourism campaign, “Breathe Baguio,” aimed at marketing the mountain city as a health sanctuary, banking on its natural attractions and the cool weather.
But those who work its roads are caught in a paradox—the very geography that keeps Baguio so cool may also act as a trap, limiting where toxic emissions may go.
Satellite-derived data analyzed by the Philippine Center for Investigative Journalism shows that even as Baguio’s air quality improved since its worst years, vehicle emissions have kept it in a persistently precarious state, threatening the health of the people who keep the city moving. In the second part of this investigation, PCIJ asks who bears that burden and who is accountable for a problem that neither the national nor local government has truly solved.
During this year’s Holy Week, March 29 to April 5, Baguio City’s air quality breached “unhealthy” levels multiple times according to the environment department’s air quality monitoring, and was more than twice the World Health Organization’s (WHO) 24-hour exposure guidelines to fine particle pollution.
Despite showing improvement compared to pre-pandemic averages, fine particulate matter in Baguio small enough to enter the bloodstream remains at four times a separate WHO benchmark—the annual safe limit that the Philippines has yet to adopt.
This puts Pepin and the thousands of drivers like him, who spend their days on its roads, at a higher risk than the general population.
25 years of bad air
Baguio’s air has never met the WHO’s annual safety standard—not even once in 25 years.
Using remote sensing, atmospheric modelling, and ground-based sources, researchers from the Atmospheric Composition Analysis Group (ACAG) at Washington University in St. Louis have estimated global pollution levels going back decades.
Among what is being tracked is fine particulate matter smaller than 2.5 micrometers in diameter, called PM2.5. Too small to see, these toxic particles, largely produced by burning fuel and other combustion sources, penetrate deep into the lungs and can pass into the bloodstream.
Their estimates show that Baguio’s annual PM2.5 concentrations have not fallen below the WHO’s annual safe limit since 1998. Between that year and 2023, Baguio averaged 25.15 micrograms per cubic meter (μg/m3), or five times the WHO threshold of 5 μg/m³ annually, which is the final safety guideline.
The Philippines uses a far more lenient standard than WHO’s. (See sidebar: Measuring Baguio’s Air)
At its worst, in 2010, Baguio was the most polluted city in the country.
Rhenan Diwas, head of Baguio City Environment and Parks Management Office, attributes this peak to the land conversion boom in the city: the transformation of green to grey, the rise of condominiums, and the conversion of residential land to commercial use.
Even during the pandemic lockdowns, when traffic vanished and air pollution fell to a record low of 15.51 μg/m3 in 2020, the air remained three times the global threshold.
Since then, concentrations have been creeping back up, reaching 22.84 μg/m3 in 2023, though still below the city’s pre-pandemic average of 26.17 μg/m3.
In 2023, Baguio recorded lower PM2.5 concentrations than most cities in Metro Manila, a shift that Diwas said could be due to stricter zoning enforcement and roadside emissions testing, where drivers are fined and vehicles might be taken off the road if their exhaust appears black.
Reading the air up close
Satellite-derived data like ACAG’s estimates may show the long view. But ground stations offer high-accuracy measurements at specific local points, directly at the breathing level.
Environment regulators had long relied on a manual system that exposed paper filters for 24 hours, then weighed them to measure fine particulate matter in the air.
But in April 2025, the Department of Environment and Natural Resources-Environmental Monitoring Board (DENR-EMB) in the Cordilleras launched a continuous air quality monitoring station at Burnham Park—the region’s first official real-time sensor—with readings updated every 15 minutes on a public portal.
One year of readings, from April 11, 2025 to April 5, 2026, recorded an average PM2.5 concentration of 14.41 μg/m3. It is well within the Philippines’ AQI of “good,” but about three times the WHO annual guideline.
The worst single day was New Year’s Day, when concentrations spiked at 73.23 μg/m3. Jean Borromeo, the officer-in-charge of the DENR-EMB Cordillera, attributed this peak to firecracker use.
But outside the expected peak brought by New Year festivities, PM2.5 concentrations began bordering and crossing into unhealthy territory during the days leading to Holy Week and the December holidays.
This period is what experts and officials say is linked to the surge of tourists into the city.
Baguio receives over a million tourists annually. The tourism department recorded about 118,000 visitors in the final two weeks of 2025 alone.
Measured against the WHO’s 24-hour exposure guideline of 15 μg/m3, which should not be exceeded more than three to four times a year, Baguio’s air crossed that threshold two out of every five days between April 2025 and 2026.
Borromeo said Baguio’s readings are “mostly good and fair,” following the country’s standards.
Yet the city had already hit the WHO’s allowance in just the first week of monitoring when the new station launched.
When asked about the gap between the Philippine AQI’s “good” at 25 μg/m3 and the WHO’s final guideline at 5 μg/m3 per year, Borromeo responded, “We just follow WHO.”
The Philippine standards align with the WHO’s least stringent interim target, which is five times less strict than the final guideline.
But environmental group Greenpeace Philippines had said the country’s current standards are not enough.
“[I]n the Philippines, air pollution is still left unchecked. There is a lack of data on how bad the problem is because of the outdated air quality standards and the lack of adequate air pollution monitoring systems,” it said in a statement in 2023.
A city choking on its own success
The volume of vehicles compounds the problem. Baguio’s streets were designed for 20,000 vehicles, which was breached as early as 1988, according to a 2019 study by the now Department of Economy, Planning, and Development.
Baguio City Mayor Benjamin Magalong has said the city has 59,000 registered vehicles, with an additional 28,000 vehicles passing through daily.
City environment chief Diwas also said the mountain city has a resident population of 360,000, which nearly doubles during the day.
Those numbers come at a cost.
International air quality monitoring group Clean Air Asia, which partnered with the city government, found that road emissions dominate Baguio’s pollution profile: 94% of criteria air pollutants and 24% of climate pollutants come from the transport sector.
Clean Air Asia found that jeepneys are the leading source of carbon dioxide emissions. UV Express units contribute most of the particulate matter and black carbon, while motorcycles emit large amounts of non-methane volatile organic compounds and carbon monoxide. Buses, meanwhile, are the main source of sulfur dioxide.
But it is not just the volume of vehicles. Baguio’s geography is working against it too.
Experts like Dymphna Javier, a professor at the University of the Philippines Baguio and former dean of its College of Science, explained the city’s cool climate makes thermal inversion more likely–a phenomenon that acts like a kind of lid where warm air above traps cooler, pollution-laden air close to the ground, preventing it from dispersing upward. The inversion typically breaks after sunrise, when the sunlight heats the ground.
Sitting on a plateau surrounded by higher peaks, the city also has little room for pollutants to escape horizontally.
In effect, the city holds its own pollution in place until rain washes it down or a shift in wind direction provides an escape.
Breathing it in
Air pollution is often called a “silent killer.” In 2023, it was the second leading risk factor for early death globally, linked to one in eight deaths, according to the State of Global Air Report.
Long-term exposure to PM2.5 is associated with heart disease, stroke, diabetes, and lung damage. Children face impaired lung development, while older adults face increased risks of neurodegenerative disease and dementia.
In Baguio, the latest city-level State of Global Air Report data showed that an estimated 130 people died from air pollution-related causes in 2019. Because these deaths are difficult to attribute directly, scientists estimate the number could be as high as 191—nearly four lives lost each week.
The risks are even higher for those most exposed—jeepney drivers, whose open-air vehicles and long shifts of 10 to 12 hours on congested roads leave them continuously breathing the exhaust around them.
A 2023 study by the Manila Observatory tracked jeepney drivers in Quezon City using portable air sensors. Over 10 to 12-hour shifts, drivers were exposed to PM2.5 levels averaging 36.4 μg/m3.
This number is twice the average exposure of the general public and seven times higher than the WHO annual guideline, said Maria Obiminda Cambaliza, a research scientist at the Manila Observatory and former chairperson of the physics department at the Ateneo de Manila University.
Compared to the Philippines’ standards, the Quezon City jeepney drivers’ exposure is already classified as unhealthy.
Peak exposure recorded in the study exceeded 90 μg/m3, falling under the country’s “emergency” category.
She said the highest readings occurred near a shopping mall, at transport terminals, and at intersections where vehicles idled. The study also recorded elevated heart rates from drivers during the morning rush hour and when PM2.5 concentrations are high.
While conducted in Metro Manila, the findings offer a window into conditions faced by drivers elsewhere.
Archie Loyosen, 67, has been a jeepney driver and operator for almost 30 years. He describes the air now as polluted.
“Wala na ‘yung mga pine trees. Naputol, pinalitan na ng mga bahay at dumami na ang mga sasakyan. Kaya nadaragdagan na ng usok sa hangin. Parang, imbis na fresh na fresh, may kasamang mga usok,” said Loyosen, who is also the president of CABPHSJODA or Campo Sioco, BGH Compound, Balsigan, Philam, Happy Homes Jeepney Operators Drivers Association.
(We don’t have that many pine trees anymore. They were cut down, replaced by houses, plus there are more vehicles. That’s why there is more exhaust in the air. Instead of the air being fresh, it has smoke with it.)
Dr. John Wong, an epidemiologist and president of public health research firm EpiMetrics, said that drivers in Baguio could have a parallel experience, if not worse. Wong also contributed to the Quezon City jeepney driver study.
“In some cases, Baguio could be worse. Steep inclines cause more exhaust. There’s also the topography of the city, which might actually be making it worse,” said Wong.
The upshot is this: The people most exposed—the drivers who keep the city moving—are left to manage the health risks on their own. Everyone points to the same culprit: emissions. But no one owns the problem, and the drivers are left to breathe polluted air.
More in Part 2: Baguio’s jeepney drivers are paying the cost of bad air.
Reporting for this story was supported by Internews’ Earth Journalism Network and is part of Following the Fumes: A Cross-Border Report on Under-Reported Air Pollution Stories in Asia.
SIDEBAR
The standard
The current global threshold for particulates—5 μg/m³ annually—is not the standard used by the Philippines.
The Department of the Environment and Natural Resources, which introduced PM2.5 guidelines only in 2013, established the Air Quality Index breakpoints in 2020. It set the limit of up to 25 μg/m3 as “good” and up to 35 μg/m3 as “fair.” Beyond that is unhealthy territory.
This appears to be in line with the interim targets that WHO introduced as “stepping stones” for highly polluted regions still working toward the final safety guideline, with 35 μg/m3 as the least stringent. The final safety guideline was previously set at 10 μg/m3, then it was tightened to 5 μg/m3 in 2021—a year after the Philippines set its AQI.
The 2010 peak
In 2010, Baguio’s PM2.5 concentration peaked at 46.45 μg/m3—the highest recorded that year among all cities and municipalities—and was considered “very unhealthy” under Philippine standards. Neighboring La Trinidad recorded the second highest at 37.5 μg/m3, followed by San Juan City in Metro Manila at 30.93 μg/m3.
What’s polluting the air
Criteria air pollutants, such as particle pollution, ground-level ozone, carbon monoxide, sulfur dioxide, and nitrogen dioxide, are directly linked to respiratory and cardiovascular diseases. Climate pollutants, or superpollutants, including methane, black carbon, and ozone, contribute to warming temperatures while
Where the air quality is worse
Pollution in Baguio is not spread evenly across the city.
The city is closely monitoring four critical hotspots identified through the city’s own air quality devices: Bokawkan Road, University of the Philippines Drive, Leonard Wood Road, and Veterans Park along Harrison Road—streets with uphill stretches where drivers tend to accelerate to climb.
Diwas of the city’s environment office explains that the difference is due to the terrain—driving uphill causes more emissions. He recommends a careful study of how public transport routes can be rethought to lessen vehicle emissions.
What was our process in writing this story?
To produce this data story, the author used data from satellite-derived estimates and ground monitoring to quantify PM2.5 exposure in Baguio City, focusing on fine particulate matter (PM2.5) due to its associated health impacts.
To track Baguio City’s air quality over time, we used satellite-derived PM2.5 estimates from the Atmospheric Composition Analysis Group (ACAG) at Washington University in St. Louis to see a longer trend in air quality across the Philippines. Annual PM2.5 concentrations were available between 1998 and 2023. The approach was necessary due to gaps in publicly available ground-level data.
ACAG researchers note that these estimates are primarily intended for large-scale analysis. The annual data are presented as simple means within each grid, and while high-resolution datasets approximately 1-kilometer by 1-kilometer in the equator were used, they may not fully resolve fine-scale variations or “hotspots” because they rely on lower-resolution source data.
To process the data, NetCDF files were converted to raster format by adapting the R-based script written by the researchers. After conversion, average annual PM2.5 concentrations were calculated for each Philippine city in Google Earth Engine using indicative administrative boundary shapefiles from the United Nations Office for the Coordination of Humanitarian Affairs, sourced from Philippine government agencies National Mapping and Resource Information Authority and the Philippine Statistics Authority.
To complement these estimates, the author acquired PM2.5 concentrations from the DENR-EMB CAR continuous air quality monitoring portal. All findings were benchmarked against the World Health Organization annual safety limit.
Finally, to assess health impacts, this report used data from the State of Global Air Report.
Data preparation and analyses were performed in Google Earth Engine, RStudio, Jupyter Notebook, and Google Sheets. The digital terrain model of Baguio was created using QGIS and Blender.