# Evaluation of the Indoor Air Quality in Governmental Oversight Supermarkets (Co-Ops) in Kuwait
## 2 Materials and Methods
### On-Site Measurements  
In this study, six pollutants as indicators for the indoor of the Co-Ops' air quality were measured, namely, carbon dioxide CO\({}_{2}\), carbon monoxide CO, nitrogen dioxide NO\({}_{2}\), hydrogen sulfide H\({}_{2}\)S, total volatile organic compounds TVOCs, and non-methane hydrocarbons NMHC. These indoor pollutants were measured with a portable air quality monitor (Aeroqual, Auckland, New Zealand, model: Series 500) with the appropriate indoor air quality sensors (Aeroqual sensors). The operational range of temperature and relative humidity are 0 to 40 \({}^{\circ}\)C and 10% to 90%, respectively, for all the sensors. Table 3 shows the specifications of the sensors used in this study. The sensors of CO, NO\({}_{2}\), and H\({}_{2}\)S are gas sensitive electrochemical (GSE) sensor, in which a pollutant reaches the sensing electrode and an electrochemical reaction occurs causing electrons to flow at a level proportional to the pollutant concentration [17]. A common shortcoming of GSE sensors is their cross-sensitivity with similar molecules types [18]. CO\({}_{2}\) concentration is detected by a nondispersive infrared (NDIR) sensor. NDIR sensor measures the difference between the amount of light received by the detector and the amount of light radiated by the infrared lamp; hence, CO\({}_{2}\) molecules are quantified based on that difference [17]. TVOCs contamination is measured by a photo-ionization detector sensor (PID). In PID, the ultraviolet (UV) light's energy removes an electron from the VOC molecule, which becomes a positively charged molecule and as a result, a flow of current is generated. The amount of resulting current is proportional to VOC's concentration [19]. PID sensors' lenses are expected, with usage, to be contaminated by dust and/or dirt; therefore, the lens must be cleaned frequently. NMHC is measured by gas sensitive semiconductor (GSS) sensor [20; 21]. The literature has revealed that these sensors are reliable and they have been used by several studies [18; 19; 22; 23; 24; 25; 26; 27; 28].  
The sampling point height in each spot and for each pollutant was designated to match the human respiratory height (between 1.3-1.6 m). In each spot and for each pollutant, to ensure the representative number of 15-20 data points, measurements were taken at a 1 min interval and for a 15 min duration as an adaptation of the method introduced by [18], except that this study emphasized on three time intervals, namely morning, noon, and evening. Shortly after, the data were transferred directly to a PC software via USB for further data analysis. The popular times for customer visits were determined by two means; firstly, by asking the working staff at Co-Ops; and secondly, by using the information provided by Google's aggregated and anonymized data from customers who have opted into Google location history. These measurements were conducted three times: morning, noon, and evening. This was the case for each induvial pollutant in each allocated spot and for each Co-Op.  
Air temperature and relative humidity were measured with a multifunctional digital anemometer (Mastech MS6252B, Brea, California, USA). Distance and areas were measured with a laser meter (Lecia model: DISTO\({}^{\mathrm{TMD}}\)1, Zamudio, Spain).  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Sensor** & **Type** & **Range (ppm)** & **Minimum Detection Limit (ppm)** & **Accuracy of Factory Calibration** \\ \hline CO\({}_{2}\) & NDIR & 0–2000 & 10 & \(<\pm\) 10 ppm + 5\% \\ CO & GSE & 0–100 & 0.2 & \(<\pm\) 10\% \\ NO\({}_{2}\) & GSE & 0–1 & 0.005 & \(<\pm\) 0.02 ppm \\ H\({}_{2}\)S & GSE & 0–10 & 0.04 & \(<\pm\) 0.05 ppm \\ TVOC & PID & 0–20 & 0.01 & \(<\pm\) 0.02 ppm + 10\% \\ NMHC & GSS & 0–25 & 0.1 & \(<\pm\) 0.1 ppm + 10\% \\ \hline \hline \end{tabular}
\end{table}
Table 3: Sensor specifications.