By Gabrielle Frances Leung1, Miguel Ricardo Hilario1, Grace Betito1, Paola Angela Bañaga1, Xzann Gary Vincent Topacio1, Zenn Marie Cainglet1,3, Shane Marie Visaga2,3, Imee Delos Reyes1, Lyndon Mark Olaguera2,3, Julie Mae Dado2, Faye Cruz2, Joel Maquiling3, Maria Obiminda Cambaliza1,3, James Bernard Simpas1,3, Gemma Teresa Narisma2,3 , Robert Holz4, Ralph Kuehn4, Edwin Eloranta4
1Air Quality Dynamics Laboratory, Manila Observatory, Philippines
2Regional Climate Systems Laboratory, Manila Observatory, Philippines
3Department of Physics, Ateneo de Manila University, Philippines
4Space Sciences Engineering Center, University of Wisconsin-Madison, Madiscon, Wisconsin, USA
Summary (as of 13 January 2020):
- Emissions from Taal Volcano rapidly spread northward, hitting major population centers within an hour of the initial eruption.
- High-altitude winds were largely responsible for transporting volcanic emissions northward. HSRL measurements from Manila Observatory show that most of the pollution was transported above 12 km.
- Comparison of integrated aerosol optical depth over the Manila Observatory before, during, and after the ashfall shows current conditions are back to typical range after the phreatic eruption on 12 January 2020.
- Satellite retrievals show reduced emissions and plume dispersion across Luzon early morning, 13 January 2020.
At around 3:00 p.m. (0700Z) 12 January 2020, Taal Volcano in Batangas erupted, releasing large amounts of particles and gases into our atmosphere. In the following hours, the volcano continued to spew ash as the initial plume was transported northward by prevailing winds, as shown in Figure 1. Even from space, the transport of the emissions could clearly be seen moving quickly, reaching Metro Manila between 4:00 and 5:00 p.m. (0800-0900Z) shown in Figure 2, and spreading past Batanes by 11:00 p.m. (1500Z).It is well-known that volcanic eruptions threaten nearby areas through lava or lahar, but less-known are the impacts of such eruptions on our air quality. Volcanic ash and dust are emitted in the eruptions and dispersed throughout our atmosphere. These are types of natural aerosols, which are solid particulates or liquid droplets suspended in the air. Some aerosols are fine enough to be inhaled and have negative effects on human health. Hazardous gases such as sulfur dioxide (SO2) and greenhouse gases (GHG) are also released .
The Taal ashfall particles are noticeably quite different than the Pinatubo ashfall in terms of size, shape, texture. They are larger, more uncrystallized (amorphous), and more rough when pulverized. The presence and abundance of water in the Taal region has allowed magma to cool and solidify much faster than in a terrestrial eruption, much like Pinatubo’s. Nonetheless, volcanic ash, of whichever type or source, is a conglomeration of small particles of jagged glass, rocks, minerals that is hazardous to us when ingested through the respiratory system.
Most of the pollutants from the Taal eruption on 12 January were transported at high altitudes. A steam-and-ash plume was detected as high as 16.5 km above ground level by Tokyo Volcanic Ash Advisory Center . Termed a phreatic eruption, the event was driven by building pressure from steam, heated by magma . An injection with considerable vertical exit velocity and particle buoyancy associated with the high temperatures of volcanic emissions transported associated particles and gases towards higher altitudes . Although low-altitude winds were stagnant during the time of eruption, the rapid vertical transport of volcanic emissions allowed for horizontal transport by high-altitude winds northward into high population areas (Figures 1, 3), reaching as far as the North Luzon coast by 8:00 p.m. that night (1200Z).
Ashfall has been reported in many locations, including areas in Batangas, Tagaytay, Laguna, Cavite, Bulacan, and Metro Manila. PHIVOLCS has issued an ashfall advisory for CALABARZON, Metro Manila, and Central Luzon . The general public is advised to stay indoors, especially the elderly, children, and people with respiratory problems such as asthma. The Department of Health (DOH) has warned the public on the dangers of ashfall which include bronchitis-like illness, coughing, and nose-and-throat irritation . They suggest that N95 grade face masks should be used when possible, especially by those who are exposed to the ashfall, and motorists should drive with extreme caution due to low visibility and slippery roads.
Instruments at the Manila Observatory (location relative to Taal shown in Figure 2) support the reports of ashfall reaching the Metro late last night, and can help to assess current conditions as well.
The High Spectral Resolution Lidar (HSRL) measures how much light from a laser is reflected back towards the ground (called the backscatter). This can be used to determine the presence of clouds and aerosols, with higher backscatter generally meaning a higher concentration of aerosols (depending on the shape and radius of the aerosols as well). Figure 4 shows low backscatter in the time period before the eruption (the blue color on the left of the graph, around 2:30 p.m. local time; 0630Z). Rapidly, within an hour after the eruption starting from 4:00 p.m. (0800Z), larger backscatter values (i.e. higher amounts of aerosols) are observed at high altitudes around 10- 12 km as the polluted air mass was transported from Taal to Metro Manila. The top of the ash plume can not be measured by the HSRL which loses signal above 12 km due to high concentration of the ash. This supports the hypothesis of high-altitude transport as the main mechanism behind the rapid spread of Taal’s emissions. As the evening went on, the air mass began to descend until it reached the ground at 6:00 p.m. (1000Z), the same time that ashfall in Metro Manila was reported. The ash plume is still present after 13:00Z however the HSRL becomes blocked by water clouds starting near 1300Z (9:00 pm).
Aerosol optical depth or AOD is a measure of how much sunlight is prevented from reaching the ground due to aerosols and a marker of aerosol concentration. A higher AOD means that conditions are hazier. Figure 5 shows that total AOD from surface to 10km (which can be read as the AOD value at the top-most altitude) before the ashfall (8:00 a.m. to 12:00 p.m., 12 January 2020; 0000Z-0400Z) was around 0.36, which is somewhat polluted but typical for Metro Manila. Over a four-hour period during the peak of the ashfall in Quezon City (8:00 p.m. to 12:00 a.m., 12 January 2020; 1200Z-1600Z), AOD reached over four times that value (~1.66), signifying extremely hazy conditions.
More recent measurements (8:00 a.m. to 12:00 p.m., 13 January 2020; 0000Z-0400Z) show that AOD values have returned to normal (~0.34) over the Manila Observatory. Based on the latest satellite images, emissions from the volcano have decreased and prevailing winds are advecting residual emissions in the northeast direction (Figure 6).
As Taal Volcano continues to be at Alert Level 4 (hazardous eruption imminent), people in affected locations are advised to take necessary precautions and stay calm. In the days to come, the Manila Observatory will continue to monitor atmospheric conditions and air quality levels in order to better assess the level of danger posed to the general public.
We acknowledge the use of AHI data from the Japanese Meteorological Agency (JMA), imagery from the University of Wisconsin Madison Space Science and Engineering Center (SSEC) as part of the NASA CAMP2Ex (Cloud, Aerosol and Monsoon Processes Philippines Experiment) and the Cooperative Institute for Research in the Atmosphere (CIRA), and the NASA Worldview application team as part of the NASA Earth Observing System Data and Information System (EOSDIS). We also acknowledge that the University of Wisconsin High Spectral Resolution Lidar (HSRL) which is deployed at the Manila Observatory to support CAMP2Ex, and Dr. Jeffrey Reid of NRL for his invaluable comments and input.
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