Health benefits to the pediatric population from reduction of ambient particulate matter in Krakow, Poland

Air pollution is the greatest environmental threat to health in Europe and globally [1, 2] with fine particulate matter (PM_2.5) considered responsible for most health impacts. The largest anthropogenic source of air pollution is the burning of fossil fuels (coal, oil, and gas) for electricity generation, transport, industry, buildings, and households [3]. Air pollution is a risk factor for stroke, heart attacks, chronic obstructive pulmonary disease, lung cancer, and premature death in adults, and is associated with many health effects in children. These include adverse birth outcomes, infant mortality, asthma exacerbation and incidence, other respiratory illness, delayed psychomotor development, reduced child intelligence, behavioral problems, and autism [4].

Fetuses, infants, and children are uniquely vulnerable to air pollution owing to a host of biological and behavioral factors, including the speed and complexity of development and the immaturity of the biological defense mechanisms for detoxifying chemicals, repairing DNA damage, and providing immune protection [5]. Additionally, children often engage in vigorous outdoor activities, leading to higher exposure to air pollution and higher doses of pollutants reaching the lungs.

Despite improvements in ambient levels in many areas, air pollution has been identified by the World Health Organization (WHO) as a health priority in the sustainable development agenda [6]. While the relative risk for air pollution is relatively low compared to other risk factors, it has a great impact on human health because of the very large number of people affected. Environmental policies aimed at tackling air pollution have proven to be effective, with substantial health benefits [7, 8].

Kraków, the site of the present study, is the second largest and one of the oldest cities in Poland and is situated on the Vistula River in Malopolska Voivodeship. The population of the city in 2021 included over 780 000 citizens, with 120 000 children aged 1–14 yr [9]. For many years, Kraków has been one of the most polluted Polish and European cities [10–12]. Based on the estimates from ISGlobal—Ranking of Cities [13], Kraków has been classified in the 28th position (out of 858 European cities) for the highest mortality related to air pollution. Especially during the winter months, Kraków is often classified among the cities with the highest air pollution levels: for example, according to the IQAir live ranking, on January 12th, 2021, Kraków recorded the third worst air pollution in the world [14]. The high levels of air pollution in Kraków have resulted largely from the burning of low-quality coal in residential stoves and, to a lesser extent, from emissions from traffic and power plants. Moreover, the city is surrounded by communes where poor-quality coal stoves continue to be the dominant home-heating system [11].

To address this problem, in the 1990s, the municipal government initiated actions to reduce air pollution in Kraków, including a co-financing program to help citizens replace old coal stoves and boilers with electricity or natural gas [15]. However, for years, residential heating by coal has remained the major contributor to the very high levels of air pollution observed in Kraków, especially during the winter season [16]. During the last 12 yr, efforts to reduce air pollution have intensified, largely due to citizen action campaigns, resulting in greater awareness of the population.

Here, we review the actions taken by the government, the citywide trend in air pollution levels, and the estimated benefits of the change in air quality for children's health.

2.1. Policies

2.2. Trends in air quality

2.3. Health benefits assessment

2.4. Concentration-response (C-R) functions

2.5. Health benefits estimation

The Environmental Benefits Mapping and Analysis Program (BenMAP) is a tool for estimating health impacts resulting from changes in ambient air pollution. BenMAP-Community Edition (BenMAP-CE) is an open source tool developed by the U.S. Environmental Protection Agency to assess the health benefits of improved air quality [26]. In BenMAP-CE, the user enters data on air quality, area, study population, mortality or incidence rates, and dose-response functions. Based on the entered data and the selected scenario of air quality changes, the program determined the change in atmospheric air pollution and estimated the changes in the selected health effects resulting from this change. We have used log-linear model to estimate the potential benefits of air pollution reduction.

Equation of the function used in BenMAP-CE:

$$\begin{equation*}\Delta Y = {Y_0}*{\text{ }}\left( {1 - {{\text{e}}^{ - \beta \Delta {\text{PM}}}}} \right)*{\text{Pop}}\end{equation*}$$

where: ΔY is the change in health effect (number of cases),

Y_0 is the baseline incidence/mortality ratio,

β is the coefficient from epidemiological studies,

ΔPM is the change in the level of air pollution,

Pop is the study population.

We estimated the impact of long-term exposure (i.e. average annual air pollutant concentration) to air pollution on low birth weight, preterm birth, asthma incidence, and infant mortality based on the reported associations. For hospital admissions, we estimated the impact of short-term exposure (i.e. 24 h exposure on the day preceding the outcome).

Two different scenarios were used to assess the benefits for the pediatric population of Kraków.

Scenario 1 was based on the observed changes in air pollutant levels between 2010 and 2019. In this analysis, the number of cases avoided can be interpreted as the forgone benefits in 2010 from not having achieved the lower PM_2.5 levels observed in 2019.

Scenario 2 assumed a reduction in air pollution observed in 2010 to the levels recommended by the 2005 WHO guidelines for air quality [27]: for long-term (annual) exposure 10 μg m⁻³ for PM_2.5 and 20 μg m⁻³ for PM₁₀, and for short-term (24 h) exposure 25 μg m⁻³ for PM_2.5 and 50 μg m⁻³ for PM₁₀. The analysis was performed separately for PM_2.5 and PM₁₀. BenMAP-CE calculates the estimated difference in pollution levels for the chosen scenario and the median number of avoided cases, together with the 95% confidence interval estimated using the Monte Carlo iteration method.

In addition to these two scenarios, we have estimated the avoided cases of low birth weight, preterm birth, asthma incidence and infant mortality had Krakow's air quality in 2019 met the WHO 2005 guidelines.

3.1. Air pollution policies

3.2. Trends in air quality

Between 2010 and 2019, the mean annual air pollution levels in Kraków decreased for both PM_2.5 and PM₁₀ (figure 1). The annual average PM_2.5 concentrations declined by 39.1% from 38.1 µg m⁻³ in 2010 to 23.2 µg m⁻³ in 2019. PM₁₀ dropped from 56.9 µg m⁻³ in 2010 to 34.6 µg m⁻³ in 2019 (39.2% decline).

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Despite the decline of air pollution levels, the PM_2.5/PM₁₀ ratio was found to be in the range from 0.62 in year 2011 to 0.70 in 2013. This ratio indicates a major contribution of fine particles attributable to anthropogenic air pollution sources. The detailed information can be found in Supplementary material, (table S1).

In 2010, the annual air pollution concentrations exceeded the 2005 annual WHO guidelines [27] (10 µg m⁻³ for PM_2.5 and 20 µg m⁻³ for PM₁₀). Despite the fact that a total ban on burning coal, wood, and other solid fuels in boiler houses, stoves, and fireplaces was imposed in the city of Kraków on September 1st, 2019 [36], in 2019, the number of days when the daily air pollution levels exceeded the 24 h guidelines set by the WHO in 2005 was still very high: 103 d with PM_2.5 > 25 µg m⁻³; 62 d with PM₁₀ levels > 50 µg m⁻³ (figure 2). We have also observed that during the year 2020, the first year after the ban to use solid fuels entered into force, the number of days that exceeded the 24 h guidelines values was 94 for PM_2.5 and 56 for PM₁₀.

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In 2021, the WHO further lowered the annual average limits to 5 µg m⁻³ for PM_2.5 and 15 µg m⁻³ for PM₁₀, and the respective 24 h limits to 15 µg m⁻³ and 45 µg m⁻³ [40, 41].

3.3. Health estimates

This study is unique in that it assesses the health benefits to children of policy-related reductions in air pollution in Poland. There have been several attempts to assess the effect of air pollution on human health for the Polish population [11, 42–45] but only one study in the pediatric population (0–6 yr) [11].

We previously reported a significant improvement in air quality based on personal air monitoring in our Kraków cohort study of pregnant women and their children based on personal air monitoring [17]. The present analysis of city-wide air monitoring data shows a similar reduction of PM_2.5 as well as PM₁₀ levels over a recent 10 yr period in Kraków, consistent with prior reports [15, 43]. Improved air quality can be attributed in large part to major policy changes that reduce air pollution from solid fuel combustion, most importantly the phase-out and eventual ban of coal and other solid fuel for heating purposes. However, despite the reduction of levels of particulate matter, the PM_2.5/PM₁₀ ratio is still relatively high indicating that the anthropogenic sources are still the major source of air pollution.

We observed significant decreases between 2010 and 2019 in both the annual average air pollutant concentrations and the number of days with pollution levels above the then-current WHO guidelines. The reduction in air pollution was associated with substantial benefits for children's health, with the largest estimated numbers and percent reductions of avoided cases being for preterm births (28.3%), low birth weight (21.2%), asthma hospitalizations (54.2%), and asthma incidence (54.5%) among children and adolescents related to the hypothetical reduction of PM_2.5 air pollution in 2010–2005 WHO guidelines. A substantial number of avoidable upper respiratory tract infections were also estimated. The estimated number of avoided incident cases of asthma estimated in our study is much higher than the average effect (11.5% reduction) found for 18 European countries [46] when assuming a reduction in air pollution level to the annual limit of the WHO 2005 guidelines. However, the average annual PM_2.5 level for the countries included in the analysis (11.6 μg m⁻³) was considerably lower than that in Kraków. In another study by Khreis et al [47] in Bradford, England, it was estimated that 27% of incident asthma cases (0–18 yr) could be attributed to PM_2.5 air pollution and 33% of asthma incidence could be attributed to PM₁₀ air pollution (any level). In their study, reduction of PM_2.5 to the WHO 2005 annual standard of 10 μg m⁻³ was linked with a 1.6% decrease in incident asthma cases and a reduction in annual PM₁₀ to 20 μg m⁻³ with two avoided cases (0.1%), which are far smaller benefits than we observed in the present analysis; however, the annual level of air pollution estimated in Bradford for PM_2.5 was higher on average by only 1 μg m⁻³ compared to the WHO 2005 standard.

The reference level chosen in this analysis was based on the guidelines in force for the years considered in this analysis. However, we note that in September 2021, new more stringent Guidelines for Air Quality were published by the WHO: annual average, 5 µg m⁻³ for PM_2.5, 15 µg m⁻³ for PM₁₀, 24 h average, 15 µg m⁻³ for PM_2.5; 45 µg m⁻³ for PM₁₀ [40, 41, 48].

This report underestimates the true impact of improved air quality in Kraków. In this analysis, only a few outcomes were considered: those for which reliable data on dose-response functions were available from studies that included at least one European. For example, only cases of morbidity requiring hospital admissions were considered, omitting ER visits and illnesses not requiring medical intervention [49]. For the analysis of the short-term effects we used the hospitalization data based on the NHF records, which are public payer data. There may be some underestimation of the total number of hospital admissions because of this. However, in Poland there is a very limited number of hospitalizations not reimbursed by NHF due to obligatory health insurance for all workers (including those who are self-employed, run a business, etc) and their families. Even private hospitals have a contracts with NHF which is paying for hospitalizations. For the analysis of asthma incident cases we have used incidence estimates from the Global Burden of Disease for Poland, not Krakow-specific ones. One can assume that the true asthma incidence in Krakow is higher than those country-wide: a study conducted in different Polish regions showed that the prevalence of asthma in the age groups 6–7 yr and 13–14 yr in Krakow population is one of the highest among populations included [50]. Furthermore, owing to the lack of available data, our analysis did not include ultrafine particles; however, a recent meta-analysis revealed that this fraction of PM increased the number of asthma exacerbations, subsequent emergency room visits, and hospital admissions in children [51]. Finally, neurodevelopmental, cognitive, and behavioral effects associated with PM were not included in the analysis. However, even the present limited analysis demonstrates the large potential benefits related to the observed reduction in air pollution.

This study estimated substantial health benefits to children in Kraków starting in utero, that were attributable to clean air policies restricting the use of coal and other solid fuels. Kraków can provide a model for other cities in Europe and elsewhere that are affected by coal pollution and have high rates of preterm birth, low birth weight, and respiratory illness.

This study was supported by a grant from an anonymous foundation.

The data cannot be made publicly available upon publication because they are not available in a format that is sufficiently accessible or reusable by other researchers. The data that support the findings of this study are available upon reasonable request from the authors.

The authors declare no conflict of interest.