The study accumulated a total spore index of 190,096 spores per cubic metre of air over the nine-month monitoring period. Six primary spore types were identified in the atmospheric samples, and the vast majority were dominated by two familiar fungal genera: Cladosporium and Fusaroid-like spores. Cladosporium ranks among the most ubiquitous airborne fungi worldwide, while Fusaroid-like spores belong to a group of fungi with significant agricultural and clinical importance. Their dominance in Laoag’s air mirrors patterns documented in other tropical and subtropical locations, from Havana to Bangkok to Singapore, suggesting that these genera thrive under warm, humid conditions characteristic of Southeast Asian climates.

One of the most striking findings concerns the apparent paradox between seasonal and daily patterns. Most of the cumulative seasonal spore load was recorded during the wet season, when humidity and rainfall create ideal conditions for fungal growth and sporulation on plant surfaces, soil, and decaying organic matter. Yet the highest daily spore concentrations were observed during the dry season. This counterintuitive result likely reflects the complex interplay between spore production and atmospheric dispersal. During dry periods, spores that have accumulated on surfaces can be more readily liberated into the air by mechanical disturbance, while wet conditions may wash spores out of the atmosphere or trap them in moisture films that prevent their release.

The diurnal patterns proved equally revealing. Peak concentrations of airborne fungal spores occurred during the early morning hours between midnight and 06:00, a finding consistent with the circadian rhythms documented in fungi. Many fungal species have evolved internal biological clocks that govern the timing of spore release, often synchronizing liberation with conditions that maximize survival during atmospheric transport. Research has shown that the timing of fungal spore release can dictate survival during atmospheric transport, with early-morning release potentially allowing spores to avoid the harshest midday conditions that would desiccate them before they reach new destinations.

Statistical analysis of the relationships between spore concentrations and meteorological variables uncovered significant positive associations with relative humidity and rainfall, alongside significant negative associations with temperature. These findings suggest that warm, dry conditions suppress airborne spore loads in Laoag, while humid, rainy periods enhance them. The negative temperature association may seem surprising given that fungi generally grow faster in warm conditions, but it likely reflects the overriding importance of moisture availability. In tropical monsoon climates, temperature remains relatively stable year-round, while humidity and rainfall fluctuate dramatically between wet and dry seasons, making moisture the limiting factor for fungal activity.

Notably, wind-related variables showed no significant association with airborne fungal spore concentrations at the study site. This absence of a wind effect contrasts with findings from temperate regions, where wind speed often correlates strongly with spore dispersal. In Laoag’s coastal monsoon environment, the prevailing winds may be relatively consistent, or the local spore sources may be sufficiently close to the sampling site that dispersal distance is not the primary constraint on atmospheric concentrations. The researchers suggest that temperature, relative humidity, and rainfall together contribute to the temporal variation in airborne fungal spore concentrations at the study site.

The significance of this baseline extends beyond academic curiosity. Airborne fungal spores are major constituents of atmospheric bioaerosols that influence environmental exposure, ecosystem processes, and respiratory health. Fungal allergens have long been recognized as triggers of asthma and allergic rhinitis, and studies across multiple regions have documented correlations between spore concentrations and hospital admissions for respiratory conditions. Research has shown that fungal spores impact asthma prevalence and hospitalization rates, and allergen sensitization to fungi varies geographically. In the Philippines, where respiratory diseases remain a significant public health burden, understanding when and why spore concentrations peak could inform exposure warnings and clinical preparedness.

Agricultural implications add another layer of relevance. Many of the fungal genera detected in Laoag’s air, including Fusaroid-like spores, are associated with crop pathogens that threaten food security. The northern Philippines is an agricultural region where rice, corn, and vegetable farming are economic mainstays, and airborne spore monitoring could serve as an early warning system for pathogen pressure on crops. Climate change is expected to alter fungal disease dynamics globally, with warming temperatures and shifting rainfall patterns potentially expanding the range and intensity of crop pathogens. Baseline data on natural spore abundance provides a reference point against which future changes can be measured.

The study addresses a critical gap in Southeast Asian aeromycology. Despite the ecological and public health significance of airborne fungi, long-term outdoor monitoring data describing their temporal dynamics and meteorological relationships remain limited in the region. The Philippines has only a handful of prior aeromycological studies, including a 1970 atmospheric mold spore count in Cebu City and more recent indoor air studies in Metro Manila hospitals and schools. The Laoag study represents the first comprehensive outdoor assessment in northern Philippines and one of the few in the entire country to employ rigorous sampling over an extended period spanning both wet and dry seasons.

The research team, led by Angelli M. Llorando as part of her graduate research under the supervision of Maureen B. Sabit, with Reuel M. Bennett contributing taxonomic expertise, was supported by funding from the Department of Science and Technology through the Philippine Council for Health Research and Development and the Accelerated Science and Technology Human Resource Development Program. The datasets generated during the study are available from the corresponding author upon reasonable request. As climate patterns shift and urbanization expands across Southeast Asia, this baseline provides a foundation for future environmental monitoring, agricultural management, and respiratory exposure studies in the region, offering a template for how coastal monsoon cities can track the invisible fungal cargo circulating in their air.

Subject of Research: Environmental Science

Article Title: Occurrence, temporal variation, and meteorological drivers of airborne fungal spores in Laoag City, northern Philippines

Article References: Llorando, A. M., Bennett, R. M., & Sabit, M. B. (2026). Occurrence, temporal variation, and meteorological drivers of airborne fungal spores in Laoag City, northern Philippines. Environmental Monitoring and Assessment, 198(9), Article 993. https://doi.org/10.1007/s10661-026-15814-z

Image Credits: AI Generated

DOI: 10.1007/s10661-026-15814-z

Keywords: aeromycology, fungal spores, bioaerosols, Philippines, monsoon climate, environmental monitoring, respiratory health, Occurrence, temporal, variation, meteorological, drivers