Ozone and Multi-Pollutant Dynamics: Indoor Chemistry and Exposure Risks in Printing Environments in University Campus Area, Delhi, India

Urban air pollution in the Anthropocene increasingly reflects mixed emissions from both traditional outdoor sources and emerging indoor technological activities. Among these, printing and photocopying shops constitute important yet understudied microenvironments within academic institutions such as University of Delhi, where students and informal-sector workers experience routine exposure to diverse pollutants in confined spaces. To characterise pollutant composition, indoor chemistry, and associated health implications in these settings, we monitored ozone (O₃), PM₂.₅, PM₁₀ and NO₂ across three contrasting printing environments in University of Delhi: an open-front photocopy shop in Hindu College (North Campus), a semi-enclosed photocopy room in South Campus, and a closed indoor flex-printing facility in commercial area nearby (Malka Ganj, Delhi). Continuous measurements were conducted during the monsoon season (1 August–30 September 2025) at 15-minute intervals between 11:00–17:00, alongside temperature and relative humidity observations.

Ozone concentrations remained consistently low (16–22 ppb) across all microenvironments, influenced by the modest O₃-generation capacity of photocopiers and monsoon-season conditions that favour rapid ozone scavenging via humid surfaces and co-emitted NO. In contrast, pronounced multi-pollutant interactions emerged in the semi-enclosed and enclosed settings. Strong O₃–NO₂ correlations (r = 0.75 and 0.72, respectively) highlight the role of shared machine-driven emissions coupled with restricted dilution. Likewise, the very high PM₂.₅–PM₁₀ correlations (r = 0.93 in the semi-enclosed shop; r = 0.80 in the flex-printing room) confirm distinct particulate-generation mechanisms: fine-particle–rich emissions from heated toner units in photocopier rooms and coarse, solvent-associated particulate bursts from flex-printing operations. The enclosed flex environment exhibited the largest PM excursions, marking it as the most pollution-intensive indoor printing microenvironment.

A structured worker survey revealed frequent symptoms (eye/throat irritation, cough, headaches, fatigue) and a lack of safety training for over 70% of operators. As most photocopy shops in Delhi operate in narrow, poorly ventilated galis, real-world exposures may exceed those observed in the monitored sites.

Collectively, these results demonstrate that microenvironmental design and ventilation strength fundamentally regulate indoor pollutant composition, chemical interactions, and human exposure risk. The findings emphasise the urgent need for ventilation-oriented design standards, emission-reduced printing technologies, and targeted occupational-health safeguards within densely populated institutional and urban commercial settings.