Investigating the Influence of Air Pollution Sources on Precipitation Chemistry at Key Sampling Sites in Luzon, Philippines

Date of Award

12-1-2023

Document Type

Thesis

Degree Name

Master of Science in Atmospheric Science

First Advisor

Maria Obiminda L. Cambaliza, PhD

Abstract

Rainfall is an efficient medium for removing air pollutants, especially water-soluble ions, in the atmosphere. The comprehensive and long-term monitoring of acid deposition in the Philippines by the Acid Deposition Monitoring Network in East Asia (EANET) facilitates the investigation of the status of rainwater acidity and composition at key sampling sites in the country. These sites are located at (1) Manila Observatory (MO), Quezon City, Metro Manila (urban site, from year 2000 to 2016, and in 2019); (2) University of the Philippines Los Baños (UPLB) National AgroMet Station, Los Baños, Laguna (rural site, year 2000 to 2016); and (3) Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA) Meteorological Observation Station, Mt. Santo Tomas, Benguet (remote site, year 2006 to 2016). The rainwater samples collected in the aforementioned sites were analyzed for anions (SO42-, NO3-, and Cl-), cations (NH4+, Na+, K+, Ca2+, and Mg2+), electrical conductivity, pH, and precipitation. This study utilized neutralization factor, enrichment factor, Positive Matrix Factorization (PMF), air mass back trajectory analysis, and Potential Source Concentration Function (PSCF) in understanding the annual and seasonal variation of water-soluble ions in rainwater samples. The long-term data shows a high NH4+ ion concentration at the Metro Manila site during the second decade of monitoring and is typically observed during the dry season. This may be due to the stringent control of sulfur dioxide, the precursor of SO42-, which is the major acidic compound responsible for the neutralization of NH4+. A direct relationship between the seasonal behavior of mean pH and volume-weighted mean (VWM) electrical conductivity was observed along with the VWM ionic species in rainwater at all sites exhibiting high values during the dry season and low values in the wet season. The rainwater samples were found to be non-acidic and were usually neutralized by NH4+ and Ca2+. The results of the Positive Matrix Factorization (PMF) analyses suggest that there are four interpretable factor solutions for the three sampling sites: sea salt, anthropogenic emissions, NH4+ - K+ mix, and crustal sources. Additionally, Potential Source Concentration Function (PSCF) analyses suggest that the observed ionic species concentrations are associated with the Northeast and Southwest monsoons during the dry and wet seasons, respectively. Moreover, two separate episodes of elevated ion concentrations at the urban and rural sites were observed to be driven by tropical disturbances that can draw air masses from distant sources, thereby influencing the chemistry of rainwater samples. This study is the first comprehensive analysis of long-term precipitation data from three unique sites in Northern Philippines. The new insights gained from this study address some of our knowledge gaps on acid deposition in the country

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