Indoor Air Quality and Thermal Environment Across Three Leather Footwear Facilities in Agra India

Most of our lives unfold indoors, yet the air we breathe inside buildings is often a mystery. We tend to assume that the air inside a factory or office is simply a filtered version of the air outside, or that the temperature is a matter of personal comfort. However, the air inside a workspace is a complex mixture of what comes in from the outside world and what is generated by the people and machines within it. This indoor environment is shaped by two main forces: the weather and the building itself. The weather brings in dust and heat, while the building's ventilation—its fans, windows, and air conditioners—determines how quickly that air is refreshed and how pollutants are diluted. In many parts of the world, especially in developing economies, the quality of this indoor air is a critical but overlooked factor in worker health. When ventilation is poor, harmful particles and gases can build up to dangerous levels, affecting not just the lungs but also the body's ability to regulate heat, leading to fatigue and long-term illness.

In the leather footwear industry of Agra, India, this issue is particularly acute. The region is a global hub for shoe manufacturing, yet the industry is split into very different types of workplaces. On one end are large, registered factories with modern machinery and air conditioning. On the other are tiny, unregistered workshops, often just a single room in a house, where workers rely on basic fans or open windows. Between these extremes are small and medium-sized enterprises. While the large factories are well-known, the smaller workshops employ the majority of the workforce, and very little is known about the air quality inside them. Do the differences in building size and ventilation actually change the air workers breathe, or is the weather the main driver of pollution regardless of the facility? To answer this, researchers spent over two years monitoring the air inside three specific facilities in Agra, representing each of these three scales, to see what the air was actually like and what controlled it.

The study took place over a period of twenty-seven months, covering two full winters and two summers. The researchers visited three distinct leather shoe factories in Agra: a large, organized unit with air conditioning and mechanical exhaust systems; a medium-sized workshop with natural ventilation and some fans; and a small, cottage-style unit located in a residential building with only basic ceiling fans. They did not just take a few quick measurements; they conducted hundreds of monitoring sessions, tracking the air every minute for ten minutes at a time. They measured the amount of tiny dust particles, the level of carbon dioxide which indicates how stale the air is, and the concentration of invisible gases released by glues and solvents. They also recorded the temperature, humidity, and how fast the air was moving. By comparing these measurements across the different seasons and the different types of factories, the team could separate the effects of the weather from the effects of the building's design.

The results revealed a clear and striking pattern. The type of facility mattered far more than the season for most of the pollutants. In the small, cottage-style workshop, the air was significantly worse than in the large factory. The concentration of fine dust particles was twice as high, carbon dioxide levels were nearly double, and the levels of harmful gases from adhesives were three to three and a half times higher than in the organized facility. This difference was consistent throughout the year. While the amount of dust in the air did rise and fall with the seasons—peaking in the dry winter and dropping during the monsoon rains—the gap between the small workshop and the large factory remained constant. The large factory, with its mechanical systems, was able to keep the air cleaner regardless of the weather outside. In contrast, the small workshop had no such protection; its air quality was dictated almost entirely by the air coming in from the street and the dust generated inside the room.

The study also highlighted a severe thermal challenge, particularly for the workers in the smallest units. In the summer, the temperature inside the large factory, despite having air conditioning, still rose well above the range considered comfortable for human health. However, the situation in the cottage unit was far more extreme. The air inside was hot and humid, and critically, it was stagnant. The air velocity, or how fast the air was moving, was so low in the small workshop that it could not provide any cooling effect to the workers. In nearly three-quarters of the monitoring sessions in the cottage unit, the air was so still that it offered no relief from the heat, compounding the danger of the high temperature and humidity. This lack of air movement is a major concern because, without mechanical cooling, moving air is the only way to help the body cool itself.

One of the most telling findings involved the source of the pollution. The researchers found that in the large factory, the air inside was significantly cleaner than the air outside, thanks to filtration systems that removed half of the incoming dust. But in the small workshop, the air inside was indistinguishable from the air outside. This suggests that in these tiny spaces, the pollution generated by the work itself—such as leather dust and glue fumes—is adding so much to the air that it matches the level of pollution already present in the city. Furthermore, the study identified a specific moment when the air quality spiked: the process of pasting shoe soles. Whenever this gluing activity was happening, the levels of volatile organic compounds, which are harmful gases released by solvents, jumped significantly in all three facilities. This points to a specific, actionable problem: the gluing stations are major sources of pollution that need local exhaust systems to capture the fumes right where they are created, rather than relying on general ventilation to clear the room.

The researchers were careful to note that their findings come from just three specific buildings, so they cannot claim that every factory of this size is exactly the same. However, the consistency of the results suggests a strong link between the scale of a facility, its ventilation infrastructure, and the health of its workers. The data indicates that simply opening windows or relying on the changing seasons is not enough to protect workers in small workshops. The solution lies in improving the physical infrastructure of these spaces. Installing local exhaust fans at the gluing stations and adding simple ceiling fans to move the air could make a profound difference. While the large factories have the resources to manage their air, the vast majority of workers in the smaller, unregistered units are exposed to significantly higher levels of pollution and heat stress, a disparity that current regulations often fail to address. The study serves as a clear call to action, showing that better ventilation is not just a matter of comfort, but a fundamental requirement for safety in these essential industries.