Higher Ambient Particulate Pollution due to summer fires associated with a Higher Incidence of COVID-19 in the wider area of Athens Greece

Abstract: During the summer months of July and August 2021, Greece faced an unprecedented climate challenge as the nation was gripped by two intense heat waves, pushing temperatures to extreme levels. These prolonged periods of scorching heat set the stage for a series of devastating wildfires that swept across various parts of the country. Among the regions, most severely impacted was Attica, the densely populated area surrounding the capital city, Athens. The fires, fueled by the dry conditions and relentless heat, ravaged vast tracts of land, destroying homes, forests, and infrastructure, and creating an environmental catastrophe. The scale of the fires not only led to widespread destruction on the ground but also had significant atmospheric consequences. As the fires raged, enormous quantities of smoke and ash were released into the air, resulting in a dramatic increase in atmospheric particulate matter. This thick smoke often engulfed the skies over Attica, casting a dark pall over the region. The dense smoke effectively filtered out sunlight, leading to a noticeable reduction in the amount of solar radiation, particularly ultraviolet (UV) radiation, reaching the Earth's surface. The impact of this atmospheric disturbance was far-reaching. Reduced levels of solar UV radiation, which plays a crucial role in various environmental and health processes, combined with the elevated levels of particulate pollution, created a unique atmospheric environment. UV radiation is known for its ability to inactivate various pathogens, including viruses, by damaging their genetic material. Therefore, a significant reduction in UV exposure due to smoke could potentially influence the persistence and spread of airborne pathogens, including the SARS-CoV-2 virus, responsible for COVID-19.

Keywords: Ultraviolet solar radiation; particles; COVID-19; Athens

In this study, we delve into the possible connections between these environmental changes and the spread of COVID-19 in the Attica region during the summer of 2021. We investigate whether the combination of reduced solar UV radiation and heightened atmospheric particulate pollution created conditions that could have facilitated the transmission of the virus. Specifically, we explore the hypothesis that the decrease in UV radiation, coupled with the adverse effects of high pollution levels on respiratory health, may have synergistically contributed to an environment more conducive to the spread of COVID-19.

1. Introduction

The COVID-19 pandemic has unleashed an unprecedented global health crisis, prompting a vast body of research aimed at understanding the myriad factors that contribute to the transmission and severity of SARS-CoV-2, the virus responsible for the disease. Among these factors, the role of environmental conditions—specifically weather patterns, air pollution, solar radiation, wildfires, and airborne dust—has garnered considerable attention. These elements are crucial not only because of their direct impact on human health but also due to their potential influence on the spread of infectious diseases, including COVID-19.

One significant area of study has focused on particulate matter (PM) pollution, a common byproduct of industrial activities, vehicular emissions, and natural phenomena like wildfires. Particulate matter, particularly fine particles such as PM2.5 and PM10, has been linked to a range of adverse health outcomes, including respiratory and cardiovascular diseases. Given that COVID-19 primarily affects the respiratory system, understanding the relationship between PM pollution and the spread of the virus has become a critical area of inquiry. Research conducted by Zhu et al. [1] in China provides compelling evidence of this relationship. Their study revealed that for every 10 µg/m³ increase in PM2.5 and PM10 levels, there was a corresponding 2.24% rise in COVID-19 cases and a 1.76% increase in mortality. This suggests that higher levels of air pollution may exacerbate the spread and lethality of the virus, likely due to the aggravating effects of particulate matter on respiratory health, making individuals more susceptible to severe outcomes if infected.

The impact of wildfires on air quality and public health has also been a focal point of recent research, particularly in the context of the COVID-19 pandemic. Meo et al. [2] observed dramatic increases in PM2.5 concentrations following the California wildfires, with levels surging by 220.71%. This sharp rise in air pollution was associated with a 56.9% increase in COVID-19 cases and a 148.2% increase in deaths, underscoring the potential for wildfire smoke to significantly amplify the health impacts of the pandemic.

Particulate pollution from wildfires and airborne dust not only deteriorates air quality but also leads to the attenuation of solar radiation, specifically UV radiation. UV radiation, particularly UVB, is essential for the synthesis of vitamin D in the human body, which plays a vital role in immune function. Reduced exposure to solar UV radiation due to smoke and dust could lead to widespread vitamin D deficiency, potentially weakening the immune system and increasing susceptibility to infections like COVID-19. The 2020 wildfires in South America, for instance, resulted in an average monthly deficit of up to 200 W/m² in solar radiation due to aerosols released into the atmosphere [3]. Such a significant reduction in solar radiation can have profound implications for public health, particularly in terms of vitamin D synthesis. Moreover, extreme airborne dust events have been shown to attenuate Global Horizontal Radiation (GHI) by up to 40–50% and Direct Normal Radiation (DNI) by as much as 80–90% [4]. These reductions in solar radiation can have cascading effects on the population's health, potentially increasing the risk of respiratory infections and other diseases.

Several studies have highlighted the importance of maintaining adequate vitamin D levels in reducing the risk of COVID-19. For example, research conducted in China found that vitamin D deficiency (levels below 30 nmol/L) was strongly associated with a higher incidence of COVID-19, with an odds ratio (OR) of 2.72, indicating that individuals with low vitamin D levels were significantly more likely to contract the virus and experience severe outcomes [5]. Similarly, in the United States, individuals with sufficient levels of 25-hydroxyvitamin D (>50 ng/mL) were found to have a 40% lower positivity rate for SARS-CoV-2 compared to those with deficient levels (<20 ng/mL) [6]. These findings underscore the potential protective role of vitamin D against COVID-19 and highlight the need to consider environmental factors that may affect vitamin D synthesis when assessing public health risks.

In light of these findings, the present study aims to conduct an in-depth investigation into the environmental and health impacts of the wildfires in Attica, Greece, with a particular focus on the Varympompi fire that occurred on August 3–4, 2021. The study seeks to address the following key objectives:

Quantification of Particulate Pollution: The study will first quantify the magnitude of particulate pollution in the Attica region resulting from the Varympompi fire. This involves assessing the levels of PM2.5, PM10, and other pollutants released into the atmosphere during and after the fire, providing a comprehensive understanding of the air quality degradation in the region.

Relationship Between Pollution and Solar Radiation: The study will investigate how the particulate pollution from the wildfires impacted surface solar radiation, particularly UVB radiation, in Attica. This includes analysing data on solar radiation levels before, during, and after the fire, to determine the extent to which particulate matter attenuated solar radiation. Furthermore, the study will explore whether this reduction in solar radiation influenced the spread of COVID-19 in the region, considering the potential for decreased UVB exposure to contribute to vitamin D deficiency and heightened vulnerability to the virus.

Spatial Analysis of Affected Areas: The study will identify and map the areas of Attica that were most severely affected by particulate pollution and the consequent attenuation of UVB radiation. This spatial analysis will help to pinpoint specific regions where the environmental impacts of the fire may have been particularly acute, allowing for targeted public health interventions and further research.

Impact on COVID-19 Health Metrics: Finally, the study will evaluate the impact of these environmental factors on daily COVID-19 case counts, ICU admissions, and mortality rates in Attica. By correlating data on air pollution and solar radiation with health outcomes, the study aims to provide a clearer picture of how environmental degradation following a wildfire can exacerbate the public health challenges posed by a pandemic.

Through this comprehensive investigation, the study aims to contribute valuable insights into the complex interplay between environmental events like wildfires and the spread of infectious diseases such as COVID-19. The findings will have important implications for public health policy, particularly in regions prone to wildfires and other environmental hazards, highlighting the need for integrated strategies that address both environmental and health risks in the context of a changing climate.

2. Data and Methodology

The datasets were obtained for the period 20 July–10 September 2021, and include (a) the daily number of COVID-19 cases, deaths, and intensive care unit (ICU) admissions in Attica from the National Public Health Organization, (b) daily UV values of solar radiation (UVB) from the measuring station of the Biomedical Research Foundation of the Academy of Athens, and (c) daily values of particulate pollutants (PM1, PM2.5, and PM10) from the particulate matter recording networks PANACEA and ATH-ENVICARE.

More specifically, concentrations of particulate pollution (µg/m³) were obtained for the Northern Sector of Attica (ATH-ENVICARE-2), for the Southern Sector of Attica (PANACEA-AirPaP-008), for the Central Sector of Attica (ATH-ENVICARE-0), for the Western Sector of Attica (PANACEA-014), and the Eastern Sector of Attica (PANACEA-AirPaP-014). The present investigation concerns the Regional Units of East Attica, West Attica, Northern Sector of Athens, Western Sector of Athens, Central Sector of Athens, and Southern Sector of Athens. We applied the NOA HYSPLIT model to capture the forward trajectories of the gas masses for 500 m, 1500 m, and 3000 m, starting from Varybombi at 18:00 UTC on 3 August 2021, for the next 96 h.

Our study estimated the effects of air pollution and UV radiation on the spread of COVID-19, disease severity (ICU admissions), and mortality from the Generalized Linear Models (GLM) with Poisson distribution. In the model fitting process, we used dependent variables, the daily values of COVID-19 cases, ICU admissions, and deaths, while as independent covariates we used the daily values of atmospheric particles (PM1, PM2.5, and PM10) and UVB radiation. The Poisson distribution was used to estimate the incidence relative risk (IRR) of atmospheric particles PM1.0, PM2.5, PM10.0, and UVB radiation in COVID-19 cases and ICU admissions.

3. Discussion and Results

During July and August 2021, Greece was severely impacted by two prolonged and intense heat waves, where temperatures soared between 38°C and 45°C. This extreme weather led to a number of detrimental effects on the environment, particularly in the region of Attica, which encompasses Athens. According to research by Masoom et al. [7], the meteorological conditions in Athens during this period were characterized by sustained high temperatures, extremely dry air, low wind speeds (less than 5 on the Beaufort scale), and an almost complete absence of rainfall. These harsh conditions created a highly combustible environment, with dry biomass becoming a significant fire hazard. Consequently, the region experienced rapid and uncontrollable forest fires [8].

In addition to the immediate danger posed by the fires, the atmospheric conditions further deteriorated due to the high levels of smoke and particulate matter released into the air. The smoke from the fires significantly increased the atmospheric pollution in Attica, leading to a substantial decline in air quality. This situation was exacerbated by the presence of high concentrations of African dust over Greece, which is a common phenomenon during the summer months. The combination of smoke and dust created a hazardous atmospheric environment that posed significant health risks to the population [7]. The first major fire during this period erupted on 3 August 2021 in Ano Varybombi, a suburb located to the north of Athens. This fire was followed by two more on 16 August 2021: one in Markati, a village in the municipality of Lavreotiki, and another in the Vilia region of Western Attica. The Vilia fire was particularly stubborn, as it reignited on 23 August 2021, further compounding the difficulties faced by the firefighting teams and local communities [9].

To understand the spread of the smoke from these fires, the NOA HYSPLIT (National Oceanic and Atmospheric Administration Hybrid Single Particle Lagrangian Integrated Trajectory) model was applied. The analysis revealed that after the Varybombi fire, the atmospheric circulation patterns directed the smoke in a southerly direction. The smoke from the fires traveled significant distances from the source, with air masses at different altitudes carrying the pollutants to various regions. Air masses at 1500 meters and 3000 meters altitude were found to have transported the smoke as far as Africa, affecting countries like Libya and Nigeria. Meanwhile, air masses at 500 meters altitude moved southward towards Crete, and from there, they drifted eastward, reaching Cyprus. This wide distribution of smoke indicates the extensive environmental impact of the fires, not just locally within Greece but also across broader regions in the Mediterranean and beyond (Figure 1).

The southern, northern, and central regions of Attica were most affected by the particulate pollution caused by the fire because of the southerly direction of the atmospheric circulation. The highest values were recorded on 4 August 2021 in the Southern Sector of Attica (PM1: 85.40 µg/m³, PM2.5: 148.64 µg/m³, PM10: 168.20 µg/m³) followed by the Northern Sector (PM1: 79.70 µg/m³, PM2.5: 119.02 µg/m³, PM10: 133.88 µg/m³), the Central Sector (PM1: 76.58 µg/m³, PM2.5: 118.39 µg/m³, PM10: 124.75 µg/m³), the Eastern Sector (PM1: 34.31 µg/m³, PM2.5: 51.30 µg/m³, PM10: 55.82 µg/m³), and the Western Sector (PM1: 26.34 µg/m³, PM2.5: 37.15 µg/m³, PM10: 40.28 µg/m³).

Figure 1. Forward trajectories 96 h at 500, 1500, and 3000 m AGL from NOAA HYSPLIT model starting at Varympompi on 3 August 2021, 18:00 UTC.

Our analysis found an outbreak of the pandemic between 4 and 31 August 2021 in the Southern and Central Sectors of Attica, which were significantly affected by the particulate pollution of the fires. The Southern Sector showed increased ICU admissions for COVID-19, and the Central Sector showed increased ICU admissions and deaths. In the remaining Sectors, no burden of the epidemiological indicators of the COVID-19 pandemic was observed (Figure 2).

In our study, we also examined the effect of smoke on daily integrals of UV-B radiation (Joules/m²) and CIE erythema (Joules/m²) acquired by BRFAA. A significant decrease of about 50% during the period of fires compared to previous days has been recorded for both UV-B radiation and CIE erythema. For brevity’s sake, only the graphs for the Central Sector are presented, depicting the impact of UV-B radiation and CIE erythema on COVID-19 cases, ICU admissions, and deaths (Figure 3).

The application of GLM with Poisson distribution was performed on our datasets both on the same day and lag days (up to 15 lags in advance). The exponential form of the regression coefficients (i.e., exp(β) for each of the pollutants, UV-B radiation, and CIE erythema), which are reported as the incidence rate ratios (IRRs), along with the corresponding p-values to show significance were calculated. On the one hand, the GLM outputs indicated the statistically significant positive influence of particulate matter only on COVID-19 cases (the estimated IRR (p < 0.05) was observed at all lags, i.e., an increase of 10 µg/m³ in mean daily PM2.5 (lag7) was significantly associated with an increase of 4% in daily COVID-19 cases). On the other hand, the negative impact of UV-B radiation and CIE erythema on COVID-19, especially in the Central Section of Athens, was estimated, although the results were not statistically significant (p > 0.05). This could be attributed to the short period examined in our study.

Figure 2. The effect of particulate pollution from the fires in Attica on the spread (Cases) (left panel), severity (Intensive Care Units) (middle panel), and mortality (Deaths) (right panel) of the pandemic, during the period 20 July–10 September 2021. First row: Southern Sector of Attica; second row: Northern Sector; third row: Central Sector; fourth row: Eastern Sector; fifth row: Western Sector.

The association between reduced solar radiation and vitamin D during the wildfires in Attica was examined by Masoom et al. [7]. It was found that daily levels of vitamin D recorded reductions of 30–50% due to the significant attenuation (>60%) of UV-B radiation by wildfire smoke.

Regarding the effect of wildfire smoke on air pollution and deaths from COVID-19, our findings agree with those of Meo et al. [2], who showed a positive correlation between air pollution and COVID-19 deaths. Regarding the effect of wildfire smoke and African dust on UVB solar radiation, the results of our research agree with those of Rosário et al. [3], Kosmopoulos et al. [4], and Masoom et al. [7], which showed that an increase in air pollution and high concentrations of airborne dust led to the weakening of solar radiation.

Figure 3. The effect of UV-B radiation daily integral (upper graphs) and CIE erythema daily integral (lower graphs) from the fires in Attica on the spread (Cases) (left panel), severity (Intensive Care Units) (middle panel), and mortality (Deaths) (right panel) of the pandemic, during the period 20 July–10 September 2021.

Our study presents several distinct advantages compared to other research efforts in the same area, though it is not without its limitations. Among the key advantages are:

·         Synergistic Effects Investigation: We focused on the synergistic effect of air pollution, specifically from forest fires and airborne dust, in combination with solar radiation on the spread of COVID-19. This multifaceted approach allows for a more comprehensive understanding of how environmental factors might interact to influence the trajectory of the pandemic, which is a relatively underexplored area in current research.

·         Accurate Data Collection: Unlike many studies that rely primarily on the number of daily reported cases, our study leverages more reliable indicators, such as daily COVID-19 ICU admissions and deaths. These metrics are more likely to reflect the true impact of the pandemic on public health, as they are less susceptible to the variability and potential inaccuracies in testing and reporting that can skew case numbers.
However, our study also has several limitations that must be acknowledged:

·         Uncontrolled Variables: While we attempted to control for many factors, our study did not account for certain important variables such as the age, gender, and pre-existing health conditions (comorbidities) of individuals admitted to the ICU with COVID-19. These variables are crucial, as they can significantly influence the severity of the disease and outcomes, and their omission may impact the generalizability of our findings.

·         Vitamin D Levels: We did not include data on vitamin D levels within the population, which is an important factor given the ongoing discussions about the potential role of vitamin D in COVID-19 outcomes. This omission could limit the interpretation of the effects of solar radiation in our study.

·         Public Health Policies and Human Behavior: The study also does not take into account the variability in public health policies, human behavior, and adherence to health measures such as mask-wearing, social distancing, and vaccination rates. These factors can vary greatly between different regions and over time, potentially influencing the spread of the virus and the outcomes we observed.

·         Mobility and Population Density: Additionally, the study did not consider the effects of mobility patterns and population density, which are significant factors in the transmission of respiratory viruses. Areas with higher population density and greater mobility may experience faster and more widespread transmission of COVID-19, potentially confounding the relationship between environmental factors and the spread of the virus.

By acknowledging these limitations, we aim to provide a balanced perspective on our findings, recognizing the complexity of the pandemic and the multifactorial nature of its spread and impact.

4. Conclusions

During the summer of 2021, the region of Attica experienced a significant increase in particle pollution, particularly during the wildfires that ravaged the area. The concentration of airborne particulate matter, specifically PM1, PM2.5, and PM10, saw a marked rise, with the Southern Sector of Attica being the most affected, followed sequentially by the Northern, Central, Eastern, and Western Sectors. This pattern of spatial distribution can be largely attributed to the southward movement of atmospheric circulation, which carried the particulate matter across these regions.

The increase in particulate pollution had several downstream effects. One of the most notable was the reduction in solar ultraviolet (UV) radiation reaching the Earth's surface. This reduction is significant because UV radiation plays a crucial role in the synthesis of vitamin D in the human body. The attenuation of solar radiation likely led to a decrease in vitamin D levels among the population, which can have various health implications. Moreover, there is a growing body of evidence suggesting that vitamin D plays an important role in the immune response to viral infections, including COVID-19. Therefore, the reduction in solar UV radiation, coupled with increased particulate pollution, may have exacerbated the severity of COVID-19 cases in the region. This is evidenced by the increase in Intensive Care Unit (ICU) admissions and mortality rates during this period. The synergistic effects of diminished vitamin D levels and the direct impact of particulate pollution on respiratory health could have contributed to the worsening of COVID-19 outcomes.

However, while these observations suggest a possible link between the extreme particulate pollution caused by wildfires and the severity of COVID-19 cases, it is important to note that further research is necessary to draw definitive conclusions. The complex interplay between air pollution, solar radiation, vitamin D levels, and viral infections like COVID-19 requires more detailed investigation. Such research could provide deeper insights into how environmental factors influence public health during extreme events and could inform future strategies for mitigating the impact of similar occurrences on vulnerable populations.

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