Abstract: In urban areas, stores/shops play an important role in people’s daily routines, whether it is for work, leisure, or shopping. As urban dwellers tend to spend most of their time indoors, it becomes crucial to ensure good indoor air quality (IAQ) for a comfortable and healthy environment for both employees and customers. Proper air quality is an essential part of human health protection, and the first step in achieving this is through monitoring. Understanding the composition of the air one breathes is critical to establish effective measures to maintain good air quality. The most commonly studied IAQ pollutants are carbon dioxide (CO2), carbon monoxide (CO), particulate matter smaller than 10 and 2.5 μm (PM10 and PM2.5), volatile organic compounds (VOCs), polycyclic aromatic hydrocarbons (PAHs), nitrogen dioxide (NO2), radon, microorganisms and pollen. Many studies have investigated the sources of air pollution in stores, particularly those caused by smoking and cooking. However, the IAQ of several other frequently visited stores and shops remains largely unexplored. This study focuses on the IAQ of a type of commercial establishment that is becoming increasingly popular: home improvement and gardening stores. The aim of this research was to characterise the indoor and outdoor air quality of such stores using two monitoring systems, one indoors and one outdoors. The indoor system consisted of a low-volume sampler (FAI Instruments, SILENT Sequential Air Sampler) for collection of PM10 on 47 mm quartz fibre filters, and an air quality probe (GrayWolf, WolfSense IQ-610) for CO2, temperature and relative humidity. The outdoor system included a low-volume sampler (Tecora, Echo PM) for PM10 sampling and an optical particulate matter monitor (TSI, DustTrak DRX 8533). Data acquisition was performed every minute. A total of 17 filter pairs were sampled, 14 filter pairs during opening hours (daytime) and 3 filter pairs during closing hours (nighttime), collected simultaneously indoors and outdoors. The indoor system was positioned in three locations to give a better representation of the home improvement store, while the outdoor system remained fixed throughout the entire sampling campaign. In addition, diffusion tubes (Radiello) for passive sampling of volatile organic compounds (VOCs) and carbonyls were installed at three indoor and one outdoor site. Indoors, the diffusion tubes were installed in the paint and adhesives, wood, and bathroom furniture sections. PM10 concentrations were higher than the WHO guideline and the protection threshold stipulated by the national legislation (45 and 50 μg/m3 respectively), reaching 92.4±35.3 μg/m3 indoors and 46.8±34.6 μg/m3 outdoors during labour hours. Outdoor contributions to PM10 were mainly related to resuspension, non-exhaust emissions from traffic and biomass burning, while the indoor composition was linked to resuspension and the type of product sold in each section. Indoors, the dominant VOCs were α-pinene, limonene, and hexanal, especially in the wood section, with indoor-to-outdoor (I/O) ratios of 612, 634 and 72, respectively. The most abundant elements in PM10 inside the store were Ca, Fe and Zn, with values of 637 ± 307, 260 ± 148, 176 ± 69.5 ng/m3 and I/O ratios of 1.95, 0.78 and, 3.81, respectively. The average temperature and relative humidity were 18.3 oC and 41.7%, respectively values in accordance with the standard EN 16798-1. The average CO2 concentration during labour hours was less than 850 ppm, well below the protection limit of 1250 ppm set by the Portuguese Ordinance No. 138-G/2021 on IAQ. This study showed that the type of product sold in the premises has a strong influence on the concentration of VOCs, while particulate matter is associated with the number of customers and the type of activity carried out indoors.

Keywords: Retail store, monitoring, gravimetric sampling, VOCs, PM10