Current World Environment

Introduction

Indoor air quality (IAQ) significantly impacts human health and well-being. Suboptimal environmental air quality can lead to respiratory and other diseases among students worldwide. The current pandemic-dominated era requires more urgent actions to determine its impact burden. Recently, India has been the center of attention regarding the deteriorating air quality in winter. Not just in Delhi, but most of the northeast states started suffering from smog. The deteriorating outdoor environment has a vital role in the poor quality of the indoor air. The presence of pathogens such as bacteria, viruses, mold spores, and dust mites poses a significant health risk, especially for individuals with compromised immune systems. Developing nations, such as India, are experiencing acute pressures from air pollution and climate change. A notable knowledge gap exists regarding the interconnected and synergistic effects of weather patterns, climate variability, air pollution, and human health outcomes.^1,2.

India ranked 179 out of 180 in the Environment Performance Index (EPI) 2022 with an EPI score of 7.8³ and Indoor Air Pollution (IAP) is among the important 10 leading causes of illness in developing countries⁴. Furthermore, it is the next leading environmental health threat after inadequate water, sanitation, and hygiene, accounting for roughly twice as many deaths as urban outdoor air pollution.⁵. Although there were thousands of studies on Indoor Air Quality, there are very few related to school environments, especially in India. Schools are vital social infrastructures and the second-most important indoor environment for children, after their homes⁶. Unlike adult workplaces, schools present distinct health challenges due to children's hygiene practices and shared resources, such as pencils, which can amplify the spread of illnesses. Healthy learning environments necessitate school buildings with proper ventilation, filtered air, and openable windows to ensure students' and staff's well-being⁷. Unfortunately, many Indian schools struggle with subpar indoor air quality⁸. Classrooms, despite the absence of typical indoor pollution sources like smoking and cooking, often exhibit surprisingly high pollutant concentrations. Research studies consistently showed that classrooms tend to have higher indoor air pollutant levels than residential and commercial buildings^9,10. Particulate matter pollution is an important risk factor to the quality of indoor air in many schools, originating from a range of contributors including chalk residues, soil particles, cleaning operations, pupil activity, combustion emissions, vehicular exhaust, and industrial releases, with previous research identifying traffic emissions and occupant behavior as the key drivers of indoor air pollution in educational settings^11-29.

This paper aims to comprehensively review and synthesize existing research on the Indoor Air Quality (IAQ) status of Indian school environments, published between 2008 and 2022. This study provides a foundational framework for future researchers by summarizing the current state of knowledge. It enables them to identify key indoor air pollutants and explore strategies to mitigate their impact, particularly from outdoor sources. Additional investigations are required to examine indoor air pollution in educational settings and its corresponding health consequences, employing uniform protocols and methodologies to yield consistent and dependable data.

Materials and Methods

A comprehensive literature review was conducted by searching various academic repositories and online platforms, including  Web of Science, Scopus, Google Scholar, ResearchGate, Science Direct, and SAGE Journals, to prepare this article. Important keywords like indoor air quality, school environment, India, indoor air pollution, classroom air quality, and a combination of these keywords were used to sort out the important manuscripts from the list. Pre-classification is done in the first classification stage based on the title, area, and abstracts. After initial screening, irrelevant articles were excluded, and the remaining studies were thoroughly reviewed in their entirety.

Although there are numerous articles based on indoor air quality/pollution around the world, very few are tangled with Indian classroom conditions. Figure 1 displays the geographical distribution of the available number of articles related to indoor air quality studies on school buildings from various regions of India.

Figure 1: The Topographical Spreading of studies on IAQ in Classrooms environments of Indian Schools Click here to view Figure

From the 172 articles analysed, there are only 36 articles linked to the Indian perspectives of indoor air quality. The papers are classified into three groups based on the aim and objective for easy comparison of available articles. They are (i) Review Papers, (ii)Thermal comfort and Architectural perspectives, and (iii) Indoor air quality case studies from different parts of India. After a comprehensive examination of the reviewed articles, the extracted data are systematically organized and integrated, yielding a cohesive review that informs conclusive findings and identifies avenues for future investigation.

In the absence of India-specific Indoor Air Quality (IAQ) standards, the analyzed studies relied on international guidelines, including ASHRAE Standard 62.1-2004 for CO₂ assessment, US EPA guidelines for PM_2.5, PM₁₀, and VOCs monitoring, and WHO standards for evaluating PM_2.5, PM₁₀, SO₂, NO₂, and CO concentrations. Table 1 summarizes the IAQ standards based on WHO (2005), ASHRAE(1992), and EPA(2011).

Table 1: IAQ Standards: A summary

Results and Discussion

Review Articles

Existing scientific literature reveals a scarcity of review studies on indoor air quality in schools worldwide. Notably, a thorough search yielded only four studies specific to India, focusing on the quality of indoor air in Indian School classrooms.

The paper on the Indoor Environmental Quality (IEQ) parameters³³ provides a comprehensive analysis of existing literature on naturally ventilated educational facilities, with a specific focus on thermal comfort, air purity, ventilation effectiveness, visual ambiance, and acoustic tranquility. In this study, the IEQ has been divided into four categories for easy analysis of the corresponding articles. The components include; Thermal Comfort, Acoustic Comfort, Visual Comfort, and IAQ. From this study, it is evident that for naturally ventilated school buildings, there aren't any widely acknowledged codes or comfort standards. The next review paper ³⁴ presents a systematic review of research conducted over the past fifteen years on IEQ parameters in Indian school classrooms, providing an inclusive summary of the existing knowledge on IEQ parameters in Indian educational settings. Building-associated illness (BAI) is a significant concern explored in these studies. BAI encompasses two distinct types: Sick Building Syndrome (SBS) and Building-Related Illness (BRI)³⁵. The paper relies on Indoor Environmental Quality and its parameters that are published in around 37 journals. It includes Thermal Comfort (TC), Visual Comfort (VC), Acoustic Comfort (AcC), and Indoor Air Quality (IAQ)³⁵.

Indoor Air Quality (IAQ)

IAQ is defined as the multidimensional measure of air characteristics within enclosed spaces, encompassing physical, chemical, and biological factors. The Central Pollution Control Board's Indoor Air Pollution Report³⁶ defines indoor air quality (IAQ) broadly, encompassing both airborne pollutants and ambient conditions such as temperature and humidity, which together influence occupant well-being and performance. Indoor Air Quality is compromised by inadequate HVAC systems, chemical emissions from building materials, higher occupant density, and extended indoor residence times. These problems contribute to the buildup of indoor air pollutants, comprising a range of chemicals, organic compounds, and microorganisms, such as dust, mold, fungi, bacteria, gases, vapors, and unpleasant odors.

Acoustic Comfort (AcC)

Acoustic comfort pertains to a building's ability to safeguard its inhabitants from ambient noise, fostering an uninterrupted and secure sonic environment conducive to effective communication³³. Building noise is classified into two distinct types: (i) structure-borne noise (physical contact) and (ii) airborne noise (air transmission), each requiring unique mitigation strategies³⁷. Several acoustical factors contribute to acoustic comfort, including: (i) noise frequency, (ii) noise source characteristics, (iii) noise duration, and (iv) temporal variability³⁸.

Thermal Comfort (TC)

According to ASHRAE³⁹, thermal comfort refers to a psychological state of well-being, where an individual feels content with their thermal surroundings, a subjective assessment that varies from person to person. The factors that predominantly shape Thermal Comfort (TC) are air moisture levels (Relative Humidity), the temperature of surrounding surfaces, the ambient air temperature, and the rate of air circulation³³. Two parameters that affect TC individually are metabolic rate and clothing⁴⁰.

Visual Comfort (VC)

Visual comfort is defined as a subjective response to the quantity and quality of illumination within a specific environment at a particular time. Illuminance, Surface reflectance, Uniformity Ratio, and Glare are the major parameters that are relevant for the visual comfort of an indoor building⁴¹. Research indicates that visual discomfort in educational settings is associated with negative health effects, including frequent headaches, eye fatigue, and compromised visual acuity.

Research review ⁶ on the existing literature examines the association between the quality of air inside educational settings and the health and welfare of children, and it summarizes the major air quality management practices for indoor air around the world. The findings reveal that particulate matter levels exceeded the acceptable threshold, standing out as a prominent concern among indoor air pollutants (PM₁₀ = 50µgm^-3 and PM_2.5 = 25 µgm^-3) in many schools^1,11-29. Besides this, the paper emphasizes that comprehensive knowledge of indoor pollutant sources, emission rates, dispersion patterns, toxicological properties, chemical characteristics, and associated health risks is essential for assessing the effectiveness and cost-efficiency of IAQ control measures in schools.

Researchers published a review paper in 2018⁴² including the analysis of research papers, media reports, and reports of the Government and International Organizations based on the poor school environment and its possible effect on people.  The paper's conclusion underscores the alarming correlation between inadequate school indoor environments and detrimental health consequences for children, as supported by international scientific research.

Thermal Comfort/ Architectural Perspectives

Thermal comfort is a crucial aspect of indoor environmental quality⁴³, and ensuring the thermal comfort of occupants in classrooms is of paramount importance. In India, naturally ventilated (NV) public school classrooms are prevalent, making thermal comfort highly susceptible to outdoor environmental conditions. Notably, India lacks standardized thermal comfort guidelines, unlike the ASHRAE Standard 55. A review of 37 articles revealed that 11 papers, published between 2008 and 2022, specifically addressed thermal comfort issues in Indian school classrooms.

The study⁴³ on the thermal conduct evaluation inside an architectural studio classroom in Tumkur, Karnataka was done by a questionnaire survey. The research revealed that participants demonstrated significant adaptability to elevated indoor temperatures through behavioral adaptations, including utilization of ceiling fans, natural ventilation, lightweight attire, selective shading, and hydration. The researchers ⁴⁴ studied the behaviors of Students to the change in thermal conditions in 12 primary schools in Dehradun City in Uttarakhand. Thermal comfort was determined by questionnaire surveys and the building characteristics were also noted. The questionnaire encompassed a comprehensive data collection approach, gathering information on participant characteristics (age and gender), clothing details via a checklist, and subjective thermal perceptions through two specialized metrics: the 7-point Thermal Sensation Vote (TSV) assessing thermal sensation (from +3= Very hot, to -3 =Very cold), and the 5-point Thermal Preference Vote (TPV) evaluating thermal preference (from +2= Much warmer to -2 = Much cooler). The results indicate a notable divergence between children's subjective thermal assessments and objective physical environmental measurements, highlighting the complexity of pediatric thermal comfort.

A study⁴⁵ was conducted on the Computational Fluid Dynamics (CFD) simulation to investigate the effects of window and courtyard orientation on ventilation and thermal conditions within learning spaces of an educational building in Madurai. CFD is used as a tool to assess the numerical investigation of two different wind directions. The study found that improved thermal comfort and natural ventilation in Madurai buildings can be achieved through courtyard design optimization: 1:2 aspect ratio, strategic opening orientation, and controlled opening percentage.

A study ^46,47 conducted in non-air conditioned secondary school buildings across three Jawahar Navodaya Schools in Ambala, Chandigarh, and Panchkula, India, revealed that approximately 80% of students had acclimatized to higher temperatures. Notably, the comfort temperature range for the students in these classrooms spanned from 16°C to 33.7°C. The thermal comfort model study revealed a significant disparity, with a substantial majority (78%) of indoor operative temperatures meeting comfort standards, while a notable minority (22%) fell short of acceptable ranges. The study concludes that children employ seasonal adaptive strategies to cope with indoor temperature fluctuations, utilizing fans and cross-ventilation during summer and monsoon seasons, and layering clothing for insulation during winter.

researchers⁴⁸ carried out a study on the IAQ of Schools in India with an architectural perspective and reported that the air quality inside the building should be taken care of from the building design onwards. Effective communication and collaboration among building owners, architects, engineers, and consultants from the outset of construction is essential for achieving improved indoor air quality in designed buildings. By prioritizing building design and operation, we can fulfill our mission of providing safe and healthy environments for future generations, ultimately encouraging their wellness and improvement of life. The survey-based study⁴⁹ investigated the thermal conditions of non-air-conditioned classrooms in Tiruchirapalli, Tamilnadu. The results revealed that a significant majority (82%) of the participants reported being thermally comfortable, with their perceived thermal sensations leaning towards the cooler side.

The comprehensive study^50,51 on thermal comfort and occupant adaptive behavior in classrooms and laboratories situated in a composite climate zone in India revealed a strong correlation between indoor and outdoor temperatures, with an optimal comfort temperature range of 20-31°C. Notably, students employed various adaptive strategies to mitigate thermal discomfort, including adjusting clothing levels, modifying posture, and relocating to well-ventilated areas. A comparative analysis of thermal satisfaction levels in naturally ventilated and air-conditioned rooms revealed distinct differences. However, interestingly, the data indicated that the type of ventilation system did not significantly impact learning performance. Some researchers⁵² investigated the thermal adaptability in naturally ventilated school classrooms in Assam, revealing optimal temperature ranges of 22-23.5°C in winter and 27.3-30.7°C in summer. The occupant's adaptation to changing temperatures is mainly attained by changes in clothing patterns followed by the use of fans and closing/opening of windows.

IAQ Case studies from different parts of India

IAQ studies have been receiving augmented attention in the areas of research, government, and Policymaking due to their adverse health effects and occupants' discomfort⁵³. The Central Pollution Control Board's (CPCB, India)⁵⁴ Indoor Air Pollution Report defines Indoor Air Quality (IAQ) as the complex interplay of indoor environmental factors, encompassing pollutant levels, temperature, and humidity, which collectively impact the comfort and efficiency of the occupants inside the building. The concentration of pollutants in the indoor environment is affected by a complex interplay of factors including indoor air volume, pollutant emission rates from various sources, removal rates through chemical reactions or settling, air exchange rates with the outdoors, and ambient outdoor pollutant concentrations. These factors interact to determine the levels of indoor pollutants, highlighting the need for a comprehensive approach to managing indoor air quality⁵⁵.

Schools constitute a vital component of a society’s social infrastructures, serving as the primary setting for socialization and a significant environment for children outside of the home⁷. Good indoor air quality in classrooms is vital for the health and well-being of students and teachers. Moreover, it plays a critical role in optimizing academic performance, alertness, concentration, and overall comfort³. Common indoor air pollutants detected in educational settings encompass a range of contaminants, including suspended particles, oxides of sulphur, ozone, carbon monoxide, oxides of nitrogen, volatile organic chemicals, and airborne biological agents. These pollutants pose significant health risks to students, teachers, and staff, emphasizing the need for effective IAQ management in schools. A condensed form of the sources of air pollutants in schools’ indoor environments is given in Table 2.

Table 2: Major Pollutants and their sources in the school indoor environment

Particulate Matter (PM)

The particulate matter is an atmospheric aerosol comprising a diverse range of solid and liquid particles, including organic and inorganic compounds. PM pollution is a prominent indoor air pollutant in numerous schools, posing a significant threat to indoor air quality⁷. Based on the size of the particle present in the air, PM can be classified as, Total Suspended Particulate Matter (<100 µm), PM₁₀ (<10µm), and PM_2.5 (<2.5µm).

Carbon Monoxide (CO)

CO is a potent fragrance-free toxin, that is generated through incomplete combustion of fossil fuels, primarily from indoor sources including water heaters, gas and wood stoves, and smoking activities. The intrusion of vehicle emissions into a building's ventilation network can lead to heightened indoor CO levels, putting occupants at risk of serious health problems⁵⁶.

Nitrogen dioxide (NO₂)

Nitrogen dioxide (NO₂), a toxic atmospheric pollutant, is primarily produced during high-temperature combustion processes, where nitrogen and oxygen react to form a water-soluble, reddish-brown gas characterized by its pungent, acrid smell. Due to its detrimental effects on the environment and human health, NO₂ emissions warrant close monitoring and regulation⁵⁷. The NO₂ levels are often elevated by the use of gas-powered devices, kerosene heaters, and tobacco smoking, posing a considerable risk to the air quality of the indoor environment and human comfort.⁵⁶.

Sulphur dioxide (SO₂)

Sulphur dioxide (SO₂) is a colourless, pungent gas detectable at concentrations as low as 0.5 ppm. Primarily emitted through the combustion of sulphur-containing fuels, SO₂ is a vital component in atmospheric chemistry, serving as a key precursor to the formation of sulphate aerosols, which significantly influence cloud properties, acid rain, and air quality. These sulphates are a key component of respirable particulate matter, posing significant air quality and health concerns⁵¹.

Ozone (O₃)

The formation of ground-level ozone, a significant secondary air pollutant, occurs through photochemical reactions involving hydrocarbons, nitrogen oxides, and ultraviolet radiation from sunlight, with profound implications for atmospheric chemistry, human health, and environmental sustainability⁵⁶. This reaction can harm small plants, animals, and humans. Generally, indoor ozone concentration is less than the outdoor concentration unless there is a contributor like photocopiers, laser printers and electrostatic air cleaners⁶.

VOCs

Organic compounds, defined by the presence of hydrogen and carbon atoms in their molecular structure. VOCs are characterized by relatively low boiling points, ranging from 50°C to 260°C, making them prone to evaporation at room temperature, with examples including acetone, benzene, and formaldehyde.⁵³

Bioaerosols

Bioaerosols are airborne particles or fragments obtained from plants or animals, microorganisms, or their byproducts, including live or dead bacteria, viruses, fungi, toxins, allergens, and cellular components⁶.

A summary of the available articles discussing indoor air pollution in school buildings in India from 2008 to 2022 and their major findings are given in Table 3.

Table 3: The summary of the results of IAQ studies of school buildings in India

Discussion

Addressing poor indoor air quality in schools is crucial, as neglecting this issue can exacerbate health concerns. A proactive approach is vital for safeguarding the well-being of students and staff. The existing studies reveal that occupants in India are adapted to a temperature range of 17 - 33.7°C, despite varying climates. In non-ventilated classrooms, temperature adaptation occurs through changes in clothing, fan usage, window operation, and hydration.

Indoor air quality studies across India identify particulate matter, CO, VOCs, NO₂, SO₂, ozone, and biological agents as common pollutants in school environments. Sampling units are typically positioned 1 meter above the floor, opposite the blackboard, to measure pollutants at students' breathing zones. Case studies consistently highlight the profound influence of outer environments on the quality of indoor air. A significant majority of these studies conclude that schools situated near dense traffic areas exhibit substantially higher pollutant concentrations compared to those located in residential areas. Thus, roads with heavy traffic, children's movements, and poor ventilation rates of the classrooms can be considered as the major indoor air quality problems in schools. Poor air quality can lead to increased illness, absenteeism, and respiratory issues.

The absence of globally adopted codes and Indian standards for optimal Environmental Quality of Indoor environments in non-air conditioned school classrooms highlights a critical knowledge gap. To address this, further scientific research is necessary to establish accurate comfort limits and develop a more exact, standardized procedure that accounts for diverse climatic conditions.

Moreover, the impact of air pollution on schools warrants further investigation. Prioritizing school infrastructure upgrades can significantly enhance the learning environment, reduce disease transmission, and promote student well-being and academic performance.

Additionally, acoustic and visual comfort in schools have been overlooked, despite their importance in optimizing student performance and productivity. The development and implementation of standardized protocols and recognized models for assessing multiple comfort factors are vital for optimizing school IEQ. Therefore, developing generic methodologies and guidelines for aural and visual comfort is a pressing need.

Conclusion

This systematic review conducts a thorough investigation of existing studies on indoor environmental quality (IEQ) in Indian school classrooms employing natural ventilation strategies. The analysis concentrates on five crucial IEQ dimensions: thermal well-being, indoor air pollution, airflow rates, visual ergonomics, and aural comfort. India's ventilated school buildings remain an understudied context within the broader field of IEQ research, underscoring the importance of localized investigations.

The study points out that indoor air quality is a critical aspect that needs to be carefully considered and addressed at the design and planning stage, even before construction begins. Proactive planning and incorporation of good ventilation design, material selection, and other strategies can help prevent indoor air quality issues, ensuring a healthier indoor environment from the outset. The paper highlights the scarcity of research on indoor air quality in Indian school buildings, emphasizing the need for urgent attention to this critical issue. The available studies underscore the presence of poor indoor air quality, which can have severe implications for the health, well-being, and academic performance of students. The review also identifies significant knowledge gaps, including the lack of standardized protocols for monitoring indoor air quality and the need for studies examining the influence of climate, air pollution, and ventilation strategies on indoor air quality. To address these gaps, future research should prioritize comprehensive and longitudinal studies, incorporating multidisciplinary approaches to inform evidence-based policies and practices that promote healthier indoor environments in Indian schools.

Acknowledgement

The authors are thankful to the Registrar, University of Kerala for providing the library facilities for this study. Also acknowledge the Head of the Department of Environmental Sciences, Dr. Sabu Joseph, Professor for the help rendered during the study period.

Funding Sources

The author(s) received no financial support for the research, authorship, and/or publication of this article.

Conflict of Interest

The author(s) do not have any conflict of interest.

Data Availability Statement

This statement does not apply to this article.

Ethics Statement

This research did not involve human participants, animal subjects, or any material that requires ethical approval.

Informed Consent Statement

This study did not involve human participants, and therefore, informed consent was not required

Author Contributions

NIYATHI VIJAY: Conceptualization, Methodology, Data collection, Analysis, Writing- Original Draft

JAYA DIVAKARAN SARASAMMA: Supervision- Review and Editing.

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