## 2 Materials and Methods
### Temperature Data Collection  
Ten cities were selected for data collection, including Burlington, Cedar Falls (CF), Cedar Rapids, Council Bluffs, Des Moines, Fort Dodge, Marshalltown, Sioux City, Waterloo, and Waverly (Figure 1). Their populations range from approximately 10,000 to 210,000 inhabitants (Table 1) and thus well represent different sizes of cities typical in the state of Iowa. A total of 9 custom multi-function mobile sensor systems (Figure 2) were built by author [PERSON]. The systems were comprised of a small microcontroller (Adafruit QTPy RP2040, Brooklyn, NY, USA), a Global Navigation Satellite Systems receiver (Adafruit Mini GPS PA1010D, Brooklyn, NY, USA) and sensors that recorded air temperature and humidity (Sensiiron SH40, Stata, CH) as well as surface temperature (Melexis MLX90614, Novi, MI, \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Urban Area** & **Population** & **Area (sq km)** & **Climate Zone** \\ \hline Burlington & 23,988 & 59.8 & 5 \\ \hline Cedar Rapids & 137,728 & 143.7 & 5 \\ \hline Council Bluffs & 62,792 & 90.9 & 5 \\ \hline Des Moines & 214,124 & 267.6 & 5 \\ \hline Fort Dodge & 24,870 & 71.4 & 6 \\ \hline Marshalltown & 27,584 & 58.4 & 5 \\ \hline Sioux City & 85,784 & 80.6 & 6 \\ \hline Waterloo/CF & 108,045 & 97.2 & 6 \\ \hline Waverly & 10,395 & 54.81 & 6 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Population of each individual target city, area modeled, and climate zone by International Energy Conservation Code—IECC—[[https://base.prnnl.gov/images/iecc-climate-zone-map](https://base.prnnl.gov/images/iecc-climate-zone-map)]([https://base.prnnl.gov/images/iecc-climate-zone-map](https://base.prnnl.gov/images/iecc-climate-zone-map)) (accessed on 6 November 2024). Figure 1: Cities for which temperature data were collected. USA) and ambient light (Rohm BH1750, Kyoto, Japan), all within the Adafruit Stemma ecosystem. The precision of the thermometers was to two decimal places in degrees Celsius, and the accuracy was up to 0.2 \({}^{\circ}\)C [30]. The sensors were housed in a custom, white 3D printed semi-enclosure to protect the sensors from direct exposure to the sun and mounted on the vehicles with a large suction cup. Preliminary testing indicated mounting the mobile system on three different positions (driver's window, passenger front window, and passenger's back window on the driver's side) showed negligible difference (and within the accuracy of the devices) on air temperature measurements. Hence, devices were mounted on the driver's side windows of all vehicles that performed the measurements. Python-based scripts were developed to allow sensor communication and data collection and for post-processing of the raw data collected by the sensors. Between June and September 2022, temperatures were collected on days when daytime high temperatures were forecasted to exceed 32 \({}^{\circ}\)C during three specific time periods (afternoon--4 to 5 p.m., evening--9 to 10 p.m., and night--4 to 5 a.m.). The chosen times of the day were selected to capture the differences and intensity of air temperature in the urban environment while taking into consideration the stability of the temperature commonly seen throughout the day. The study by [PERSON] [31] established that urban areas experience their highest air temperatures between 2 p.m. and 5 p.m. (corresponding to the afternoon data collection), and densely urban areas exhibit the most significant air temperature differences compared to non-built-up regions a few hours after sunset. Moreover, the nighttime period, known to worsen health issues related to heat exposure, has been emphasized in studies [3; 32; 33], providing justification for air temperature data collection during nighttime (4 a.m. to 5 a.m.). Within each city, driving routes were carefully planned to account for various urban zones (e.g., downtown, industrial, park, residential) with diverse morphological characteristics, while also ensuring data acquisition could be completed within a 1 h limit during generally stable temperature conditions.