Manila Observatory

Abstract This study aims to understand the mechanism behind the frequent rain-induced landslides in Mount Diwata through detailed soil characterization. The shear strength parameters of soils from different landslide sites were investigated to find any correlation to the moisture content and their physical and index properties. The results of the study showed the significant influence of the grain size and soil type on the shear strength behavior. For all soil samples, an increase in the water content resulted in a decrease in shear strength and friction angles. This suggests that water saturation is the primary trigger of these slope failures since they occurred after days of heavy rain. However, while the apparent cohesion of coarse-grained soil increases with increasing water content, the cohesion of fine-grained soil initially increases when the water content increases but decreases when a specific moisture content is attained. These findings show that the soil's shear strength is primarily attributed to cohesion for fines and friction angle for the coarser particles. Since the results of the current study are localized, they can provide valuable insights to identify the most appropriate engineering interventions and remediation for this recurring problem in Mount Diwata.

<strong class="journal-contentHeaderColor">Abstract.</strong> Biomass burning and urban emissions are major contributors to poor air quality throughout Southeast Asia. Understanding these emissions is critical for predicting and mitigating their health impacts. The Cloud, Aerosol and Monsoon Processes Philippines Experiment (CAMP²Ex) field project in 2019 focused on regional sources in Southeast Asia and their effects on aerosol/cloud interactions using a combination of airborne, shipboard, and ground-based platforms. These measurements sampled a variety of pollution sources over the Sulu, Philippine, and South China seas during both the southwest monsoon and monsoon transition periods. CAMP²Ex provided a unique opportunity to examine how local and transported emissions affected airmass chemical composition and air quality. Correlations in airborne in situ gas enhancement ratios of CH₄ to CO were used to separate airmasses with predominantly biomass burning, urban, or mixed influence, and isolating contributions from differing urban sources. HYSPLIT backtrajectory analysis was used to identify airmass sources, and resulting source regimes were examined for differences in ozone, reactive nitrogen, and aerosol chemical composition. &Delta;O₃/&Delta;CO enhancement ratios were observed to be constant between urban source regimes, yet &Delta;NO_y/&Delta;CO enhancement ratios differed across these regimes. For biomass burning sources, enhancement ratios in &Delta;O₃/&Delta;CO were lower than those reported by previous studies in this region. Organic aerosol mass fractions were 2&ndash;3 times higher in biomass burning influenced regimes compared to urban regimes. This technique represents a simple yet novel approach for separating emission influences in a complex environment that enable isolation of emission sources requiring relatively simple measurements.

<strong class="journal-contentHeaderColor">Abstract.</strong> Biomass burning and urban emissions are major contributors to poor air quality throughout Southeast Asia. Understanding these emissions is critical for predicting and mitigating their health impacts. The Cloud, Aerosol and Monsoon Processes Philippines Experiment (CAMP²Ex) field project in 2019 focused on regional sources in Southeast Asia and their effects on aerosol/cloud interactions using a combination of airborne, shipboard, and ground-based platforms. These measurements sampled a variety of pollution sources over the Sulu, Philippine, and South China seas during both the southwest monsoon and monsoon transition periods. CAMP²Ex provided a unique opportunity to examine how local and transported emissions affected airmass chemical composition and air quality. Correlations in airborne in situ gas enhancement ratios of CH₄ to CO were used to separate airmasses with predominantly biomass burning, urban, or mixed influence, and isolating contributions from differing urban sources. HYSPLIT backtrajectory analysis was used to identify airmass sources, and resulting source regimes were examined for differences in ozone, reactive nitrogen, and aerosol chemical composition. &Delta;O₃/&Delta;CO enhancement ratios were observed to be constant between urban source regimes, yet &Delta;NO_y/&Delta;CO enhancement ratios differed across these regimes. For biomass burning sources, enhancement ratios in &Delta;O₃/&Delta;CO were lower than those reported by previous studies in this region. Organic aerosol mass fractions were 2&ndash;3 times higher in biomass burning influenced regimes compared to urban regimes. This technique represents a simple yet novel approach for separating emission influences in a complex environment that enable isolation of emission sources requiring relatively simple measurements.

Abstract. Biomass burning and urban emissions are major contributors to poor air quality throughout Southeast Asia. Understanding these emissions is critical for predicting and mitigating their health impacts. The Cloud, Aerosol and Monsoon Processes Philippines Experiment (CAMP2Ex) field project in 2019 focused on regional sources in Southeast Asia and their effects on aerosol/cloud interactions using a combination of airborne, shipboard, and ground-based platforms. These measurements sampled a variety of pollution sources over the Sulu, Philippine, and South China seas during both the southwest monsoon and monsoon transition periods. CAMP2Ex provided a unique opportunity to examine how local and transported emissions affected airmass chemical composition and air quality. Correlations in airborne in situ gas enhancement ratios of CH4 to CO were used to separate airmasses with predominantly biomass burning, urban, or mixed influence, and isolating contributions from differing urban sources. HYSPLIT backtrajectory analysis was used to identify airmass sources, and resulting source regimes were examined for differences in ozone, reactive nitrogen, and aerosol chemical composition. ΔO3/ΔCO enhancement ratios were observed to be constant between urban source regimes, yet ΔNOy/ΔCO enhancement ratios differed across these regimes. For biomass burning sources, enhancement ratios in ΔO3/ΔCO were lower than those reported by previous studies in this region. Organic aerosol mass fractions were 2–3 times higher in biomass burning influenced regimes compared to urban regimes. This technique represents a simple yet novel approach for separating emission influences in a complex environment that enable isolation of emission sources requiring relatively simple measurements.

Abstract In-cloud aerosol scavenging remains a large source of model uncertainty, affecting capabilities to capture the aerosol lifetime and impacts on air quality and climate. While past work quantified aerosol scavenging efficiencies (SEs) in midlatitude mixed-phase deep convection, SEs are less well known for shallower convection. We used aircraft data over the tropical west Pacific to calculate SEs for three marine cumuli of different top heights (3–7 km MSL) using a simple entrainment model and measurements of the cloud outflow and nearby clear air. Across cases, efficient scavenging was observed for sulfate (&gt;86%) and black carbon (70%–80%), while organic aerosols (53%–60%) and nitrate (61.5%) were moderately scavenged. Ammonium had a wide SE range (53%–87%). SEs of aerosol volume concentration showed near-total removal of aerosols with diameters greater than 100 nm (&gt;92%) and inefficient removal for aerosols with diameters less than 100 nm (30%–50%), associated with the preferential activation and removal of larger particles. Mass-based SEs did not differ substantially between tropical cumuli and midlatitude deep convection, attributed to the negligible mass activated at higher supersaturations. The efficient scavenging of black carbon (BC) can be explained by an enhanced hygroscopic fraction of BC based on model results from the Community Earth System Model, version 2 (CESM2), Community Atmosphere Model with Chemistry, suggesting the internal mixing of BC with more soluble species during long-range transport through the marine atmosphere. The estimates of BC SEs provide direct evidence of substantial BC removal in convection as inferred by previous work and should motivate improvements in chemical transport models. Significance Statement The scavenging (removal) of aerosols is critical for estimating the lifetime of aerosols and their impact on air quality and climate; however, scavenging efficiency remains uncertain in global models especially for shallow convection. To address this uncertainty, we calculated aerosol scavenging efficiencies in tropical marine cumuli for different aerosol species, including sulfate and black carbon. We find that scavenging efficiencies depend on aerosol composition, size, and to a lesser extent, cloud-top height. The efficient removal of black carbon is explained by high hygroscopic fractions based on a model, related to the mixing of black carbon with more soluble species during transport. The reported scavenging efficiencies can be implemented into chemical transport models to improve model estimates of aerosol removal.

<strong class="journal-contentHeaderColor">Abstract.</strong> This study characterizes the spatial and vertical nature of aerosol hygroscopicity in Southeast Asia and relates it to aerosol composition and sources. Aerosol hygroscopicity via the light scattering hygroscopic growth factor, f(RH), is calculated from the amplification of PM₅ aerosol (D_p &lt; 5 &mu;m) scattering measurements from &lt; 40 % to 82 % relative humidity during the Cloud, Aerosol, and Monsoon Processes Philippines Experiment (CAMP²Ex) between August to October 2019 over the northwest tropical Pacific. Median f(RH) is relatively low (1.26 with lower to upper quartiles of 1.05 to 1.43) like polluted environments, due to the dominance of the mixture of organic carbon and elemental carbon. The f(RH) is lowest &nbsp;due to smoke from the Maritime Continent (MC) during its peak biomass burning season, coincident with high carbon monoxide concentrations (&gt; 0.25 ppm) and pronounced levels of accumulation mode particles and organic mass fractions. The highest f(RH) values are linked to coarser particles from the West Pacific and aged biomass burning particles in the region farthest away from the MC, where f(RH) values are lower than typical polluted marine environments. Convective transport and associated cloud processing in these regions decrease and increase hygroscopicity aloft in cases with transported air masses exhibiting increased organic and sulfate mass fractions, respectively. An evaluation of a global chemical transport model (CAM-chem) for cases of vertical transport showed the underrepresentation of organics resulting in overestimated modeled aerosol hygroscopicity. These findings on aerosol hygroscopicity can help to improve aerosol representation in models and the understanding of cloud formation.