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<p>Outdoor thermal comfort is important to city dwellers' well-being and health. Pedestrians are especially sensitive to thermal environments, and their thermal comfort is expected to be at risk due to the urban heat island effect combined with climate change. Pedestrian thermal comfort assessment is crucial to comprise sustainable climate change adaptation strategy. However, pedestrian thermal comfort has been simply evaluated using the survey asking pedestrians about their comfort levels via oral or paper interviews. The survey's shortcoming is that it does not reflect the dynamics of the ever-changing environment and the resultant responder's physiology. The development of wearable sensors overcame the survey's limitation and allowed to detect human physiological responses reflecting the changes in the surrounding environment more objectively. Among several physiological parameters, heart rate(HR) is a representative proxy for physiological thermal stress reflecting environmental heat load. It can be easily monitored by a smartwatch wearing an optical blood flow sensor. Therefore, we aim to investigate the applicability of physiological thermal comfort evaluation based on pedestrians' HRs monitored using a smartwatch in real-walking settings. The experiment was conducted on four streets with an east-west orientation in Suwon, Gyeonggi-do, Korea. The four streets were selected with high or low effects of grey and green infrastructure on the streets' thermal environment based on a building-height-to-street-width(H/W) ratio of 2 and the percentage of tree canopy cover(%TCC) of 50, respectively. The 32 voluntary pedestrians walked one street a day for an hour(14:00-15:00) with a smartwatch(Mi-band4) to record HR of each pedestrian. During walking, microclimates (air and globe temperature, relative humidity, wind velocity) were monitored using a portable meteorological station. After walking, the survey was conducted by asking about their feelings while walking as thermal comfort level. We defined the thermal environment created by grey and green infrastructures as the difference between the street's mean radiant temperature(T<sub>mrt</sub>) calculated by the street's microclimates and the official air temperature from the automatic weather station. We also suggested the physiological thermal comfort index(PTCI) to quantify physiological thermal comfort including the cardiovascular risk based on HRs. Consequently, we found the tree's effect was contradictory according to the H/W ratio. The increment of 10%TCC reduced T<sub>mrt</sub> by 1.1℃ on the low H/W ratio street but rose T<sub>mrt</sub> up to 0.1℃ on the high building street. The TCC's heat dissipation hindrance might cause this result because TCC could block the wind path and interfere with air circulation rather than having the cooling effect of the tree-formed shades on streets where high buildings already form sufficient shade. The PTCI results reflected the thermal environment of each street well because a 10%TCC rise decreased the cardiovascular risk by 8% on the low building street but increased the risk up to 7% on the high building street. However, pedestrians could not perceive the thermal environments' distinctions among streets due to interruption of aesthetic quality other than microclimates. Therefore, we identified that physiological thermal comfort based on HR is more appropriate to be used as a basis for establishing adaptation strategies for pedestrians.</p>

<p>As citizens face increasing heat risk due to climate change with urban heat island effect, heat risk assessments in urban have been conducted focusing on thermal diseases related to heatwave of vulnerable people. Although they provided a basis to establish adaptation strategies such as cooling centers, they could not consider citizens’ daily thermal comfort of diverse groups. Thermal comfort could be a part of heat risk because associated with work performance such as productive capacity as well as health. In particular, pedestrians’ thermal comfort can represent daily heat risk of outdoor urban environment. The past studies of pedestrians’ thermal comfort were evaluated using PMV (Predicted Mean Vote), an index based on temperature, wind velocity, relative humidity and a fixed number of metabolic rate depending on the subject’s activity level. The PMV ranges from -3 to +3 and higher value indicates higher discomfortable. Including metabolic factor, PMV did not actually consider an individuals’ physiological response (IPR) such as heart rate, skin temperature, etc. To overcome PMV’s limitation, IPR should be considered together with climatic factors when assessing pedestrians’ thermal comfort. Therefore, we aim to develop a new function of thermal comfort by incorporating PMV and IPR, especially heart rate, with validation using personal perception of thermal comfort based on survey. We selected a route of 500m length in Suwon, South Korea and 9 volunteer pedestrians walked the selected route 8 times at 2-4 pm. The walk experiment was repeated for 4 days. During the experiment, air temperature, relative humidity, and wind velocity were monitored using portable meteorological sensors. The real-time heart rate of each pedestrian was recorded using wearable sensor (Mi-band3). After every day walk, we asked each pedestrian 10 questions regarding satisfaction of thermal environment, perceived temperature, etc. The average value of PMV was 2.99 belonging to very discomfort category. Although heart rate increased with the length of exposure time to heat, the heart rate over time did not consistently increase with air temperature. It was probably because our temperature range (31.9℃- 35.2℃) during the experiment was not large enough and heart rate was influenced by other factors such as wind velocity. In the survey, 50% of volunteer pedestrians responded ‘discomfort’ and the others answered ‘slightly discomfort’. Comparing the survey (discomfort and slightly discomfort) with PMV (very discomfort), PMV generally overestimated. thermal comfort. We will categorize thermal comfort level according to heart rate increase between walking activity in outdoor and indoor. Here, the higher heart rate increase than average increase level indicates worse individual thermal comfort condition. This individual thermal comfort effect can modify the existing calculation of thermal comfort using air temperature, wind velocity, and humidity by adding modification factor of individual heart rate response (Ex. Thermal comfort=weighting factor(0.189*air temperature-0.775*wind velocity+0.195*relative humidity)). The final thermal comfort will be calculated based on the function and examined the precision of function through comparative analysis with the personal thermal perception of survey. As heart rate is an individual variable, we expect our function can be a tool evaluating the personalized heat risk.</p>

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