The research, conducted by Hilal Arslan of the University of Health Sciences and Istanbul University-Cerrahpasa, examined the relationship between four common air pollutants and asthma hospital admissions in Sakarya between 2014 and 2018. Rather than assuming that pollution affects everyone identically and on the same day, the study asked two more sophisticated questions: how many days pass between a rise in pollution and a rise in hospital visits, and does that timing differ by age? The answers, revealed through statistically rigorous time-series modeling, point to pollutant-specific and age-specific patterns that complicate the simple picture of dirty air and wheezing lungs.

To conduct the analysis, Arslan deployed a quasi-Poisson generalized additive model paired with a distributed lag non-linear model, a statistical framework widely regarded as the gold standard for linking daily environmental exposures to daily health outcomes. The quasi-Poisson approach accommodates the overdispersed nature of hospital admission counts, which cluster unpredictably rather than following a tidy bell curve, while smoothing terms control for seasonal rhythms and long-term trends that could otherwise masquerade as pollution effects. The distributed lag component is the methodological star: it allows researchers to estimate the risk of hospitalization on the same day as a pollution spike, and at each of the following seven days, capturing the delayed biological cascade between exposure and exacerbation.

The study stratified its results across three age bands: 15 to 34 years, 35 to 64 years, and older than 64 years. For each group and each pollutant, the model calculated a relative risk per 10 micrograms per cubic meter increase in pollutant concentration. This unit, a 10-microgram increment, is the conventional yardstick of air pollution epidemiology, allowing results from different cities and continents to be compared on common ground. The findings were measured against the World Health Organization’s 2021 air quality guidelines, which tightened recommended limits for particulate matter and nitrogen dioxide based on mounting evidence that even low-level exposure harms health.

Against those guidelines, Sakarya’s air fared poorly. Concentrations of particulate matter with diameters of 10 micrometers or less (PM10), fine particulate matter of 2.5 micrometers or less (PM2.5), and nitrogen dioxide frequently exceeded WHO guideline values, with the highest pollution levels recorded during winter months. This seasonal pattern fits a well-documented dynamic in Turkish cities: temperature inversions trap cold air and its pollutant burden near the ground during winter nights, while residential heating emissions add fresh particulate matter to air that has little chance to disperse. Previous work by the same author and colleagues has linked wintertime inversion dynamics and regional transport to elevated PM10 in Istanbul and elsewhere in the Marmara region, and Sakarya appears to share the burden.

The age-stratified results delivered the study’s most striking insight. Particulate matter showed small but statistically significant associations with asthma hospital admissions among young adults aged 15 to 34, with elevated risks appearing for PM2.5 at lags of three to four days and for PM10 at lags of two to three days. In other words, a rise in fine particulate pollution today was followed by an uptick in asthma hospitalizations among young adults two to four days later. That delay is biologically plausible: airway inflammation triggered by inhaled particles takes time to build, and an exacerbation severe enough to require hospital admission typically follows days of worsening symptoms rather than striking instantaneously.

Why would young adults, whose lungs are at their most resilient, show the clearest particulate signal? The study does not settle this question definitively, but several mechanisms fit the pattern. Young adults tend to have higher outdoor activity levels and occupational exposure, spending more time commuting and working outside than retired seniors, which increases the dose of pollution actually inhaled. The elderly, despite their physiological vulnerability, may exhibit different admission thresholds or underrecognition of asthma in older patients, where diagnoses like chronic obstructive pulmonary disease or heart failure can dominate. Meanwhile, the middle-aged group of 35 to 64 years showed its own distinct signature: nitrogen dioxide, the classic marker of traffic exhaust, was positively associated with asthma admissions at lags of two to three days. Sulfur dioxide, by contrast, showed no consistent lag-specific association in any age group.

The dissociation between pollutants is itself informative. Particulate matter and nitrogen dioxide come from overlapping but distinct source mixtures, with heating and regional transport driving the former and road traffic driving the latter. Finding that PM2.5 and PM10 flagged risk in younger adults while NO2 flagged risk in the 35-to-64 group suggests that different emission sources impose different health costs on different segments of the population. For city planners, that means a single blanket policy will not address every risk equally: reducing wintertime heating emissions may protect the young adults whose admissions track particulate spikes, while curbing traffic-related pollution would target the nitrogen dioxide signal in the middle-aged cohort.

The study’s modest effect sizes deserve honest framing. A small but statistically significant relative risk per 10-microgram increment does not translate into a dramatic surge of admissions on any single polluted day, and the word small matters when communicating risk to the public. Yet from a population-health perspective, small per-person risks multiplied across millions of exposure-days and entire urban populations yield a substantial attributable burden. Air pollution is already ranked among the leading environmental risk factors for disease globally, and asthma alone affects hundreds of millions of people worldwide, so even incremental increases in admission risk carry meaningful weight for health systems operating near capacity during winter pollution episodes.

Arslan’s work also highlights a data limitation that afflicts much of environmental epidemiology: reliance on regulatory monitoring stations, which measure pollution at fixed points and may not capture how exposure varies block by block within a city. The study’s authors call for future research to integrate regulatory monitoring data with satellite-derived estimates and land-use regression models, tools that can map pollution at much finer spatial resolution and refine risk estimates by accounting for where people actually live, work, and breathe. Such hybrid approaches have already transformed exposure assessment in cities across Europe, North America, and East Asia, and applying them to rapidly urbanizing Turkish cities would sharpen the precision of the kind of age- and lag-specific findings this study pioneered. For now, the message from Sakarya is clear: the air exceeds WHO limits often enough to warrant action, the health effects arrive on a schedule measured in days, and the people most sensitive to the particulate burden are younger than conventional wisdom assumed. Targeted interventions aimed at wintertime heating emissions and traffic-related pollution, the study concludes, are needed to close the gap between the city’s air and the health guidelines designed to protect the people breathing it.

Subject of Research: Short-term age-specific effects of ambient air pollution on asthma hospital admissions

Article Title: Age-specific lagged effects of air pollution on asthma hospital admissions in Sakarya, Türkiye

Article References: Arslan, H. (2026). Age-specific lagged effects of air pollution on asthma hospital admissions in Sakarya, Türkiye. Air Quality, Atmosphere & Health, 19(10), Article 216. https://doi.org/10.1007/s11869-026-02113-2

Image Credits: AI Generated

DOI: 10.1007/s11869-026-02113-2

Keywords: air pollution, asthma hospital admissions, particulate matter, nitrogen dioxide, PM2.5, PM10, distributed lag non-linear model, time-series analysis, WHO air quality guidelines, Türkiye, environmental health, public health