Particulate matter (PM), volatile inorganic compounds (CO, CO2, NOx, O3), volatile organic compounds (VOCs), and biological pollutants together make up airborne pollutants, which is one of the foremost challenges confronting the globe today since it compromises not merely the climate (Kaur & Pandey, 2021) but also biodiversity (Agathokleous et al., 2020) and human health by elevating mortality and morbidity rates (Anenberg et al., 2021; Southerland et al., 2022; Yang et al., 2022). Particularly in developing nations such as India, the problem is exacerbated by overpopulation, unregulated urbanization, and industrialization (Gurjar et al., 2016; S et al., 2022). In Indian cities such as Delhi, Mumbai, Kanpur, and Kolkata, the mean concentration of PM 2.5, volatile organic compounds, O3 and NO2 have surged by 2.8%, 1.9%, 1.3% and 2.2%, respectively annually over the last several years (Vohra et al., 2021; Sicard et al., 2023). However, with the commencement of COVID-19, many of the countries enforced either partial or complete detentions to halt the disease's transmission, which significantly decreased the load of pollutants in the atmosphere (except for ozone) in cities all over the globe owing to minimal human activity (Kumari & Toshniwal, 2020; Gkatzelis et al., 2021; Tibrewal & Venkataraman, 2022). Considering key insights into this circumstance, the COVID-19 lockdown brings a comprehensive methodology for enhancing air quality and health, in addition to providing a baseline of adequate air quality that can be incorporated into air pollution management initiatives (Chowdhuri et al., 2021; Ravindra et al., 2022).
India, the oldest civilization in the world, and is blessed with an incredibly diverse range of cultures, customs, and traditions that are reflected in many facets of the nation (Tiwari & Patel, 2016). The cultural heritage of a country provides an automatic sense of unity and belonging within a group, in addition to socio-economic benefits (Timothy, 2014; Nugroho & Hardilla, 2020). In addition to this, 40 UNESCO World Heritage Sites serves as cultural landmarks for both the local and global people c (Bakri et al., 2012; Kaur et al., 2021). But unfortunately, over the last few decades, cultural heritage structures across the world have been under threat of being degraded by several factors, such as natural disasters (including earthquakes, floods), uncontrolled urbanization and air pollution (Themistocleous et al., 2010; Carroll & Aarrevaara, 2018). Therefore, maintaining cultural heritage sites while reducing the primary causes of this degradation is a difficult issue for the Indian government, as well as other governments throughout the world.
In accordance with stated statistics, the ever-increasing air pollution and changing climatic conditions have accelerated the deterioration of culturally important structures comprising of stone, limestone, metals, concrete, etc. (Bharti, 2013; Spezzano, 2021; Sablier and Garrigues, 2014; Metallo et al., 1995; Graue et al., 2013; Fuente et al., 2013; Karaca, 2015). However, these destructive changes are especially acute in urban centers (Saha et al., 2008; Singh et al., 2012; Miranda et al., 2017) due to the rapid development of industries, urbanization, transportation, and energy production (e.g., coal), which are the major source of aggressive air pollutants such as sulphur dioxide (SO2), nitrogen dioxide (NO2), tropospheric ozone (O3), and particulate matter (Varotsos et al., 2009; Bharti, 2013; Rao et al., 2014; Gulia et al., 2015; Spezzano 2021). In 2014, Rao et al. estimated that India losses approximately US$45 billion every year due to corrosion. Pollutants like SO2 and NO2 form H2SO4 and HNO3 acids respectively, in the atmosphere precipitates on the earth as acid rain that results in the yellowing of the white marble and limestone of the Taj Mahal (Camuffo, 1992; Sharma and Sharma, 1982; Skymet Weather Team, 2015) and tarnishing the shine of the Golden Temple in Amritsar (Camuffo, 1992; Rao, 2015). Tropospheric ozone, being the precursor of NOx and VOCs (Agathokleous et el., 2020) exacerbates the corrosion process, in addition, to a direct impact on rubber, plastic, textiles, paint, and surface coatings of cultural heritage structures (Screpanti & DeMarco, 2009; Huang et al., 2019). On the other hand, fine liquid or solid particles (particularly, PM 2.5 and PM 10) are majorly responsible for the soiling phenomenon that result in the discoloration of structures and monuments (Vidović et al., 2022). Furthermore, these aforementioned atmospheric pollutants occur concomitantly with meteorological factors such as temperature fluctuations, sunlight, wind, rainfall, and humidity, which intensifies their effects (Kumar & Imam, 2013; Rao et al., 2014; Watt et al., 2008; Turo et al., 2016; Marco et al., 2017; Rovella et al., 2020). Although the idea that air pollution damages cultural assets is commonly discussed, there is a dearth of information that can be used in studies of risk management and cost-benefit analysis of cultural buildings (Watt et al., 2008; Screpanti and Marco, 2009; Fuente et al., 2011; Spezzano, 2021).
Henceforth, the present study evaluates the baseline air quality status around 14 major heritage sites inIndiausing dose-response functions coupled with information on air pollution (PM2.5, PM10, NO2, O3, and SO2), seasonal (summer vs winter; rainy vs dry) fluctuations, and the impact of COVID-19 lockdown (pre and post-duration). Selected heritage sites are located in densely populated states of India, and many of them have already been reported for deterioration due to air pollution. The latter half of this research also states the existing policy framework regarding air pollution moderation and the scope of improvements. With the outcomes of this study, a new perspective on pollution risk to heritage structures and their preservation, along with improvising management strategies is highlighted.