Outdoor thermal physiology along human pathways: a study using a wearable measurement system

Area of Science:

• Environmental Science
• Human Physiology
• Urban Climatology

Background:

• Urban environments present complex thermal challenges for pedestrians.
• Fixed-point weather data inadequately represent individual thermal exposure in cities.
• Wearable technology offers a novel approach to studying personal microclimates.

Purpose of the Study:

• To investigate thermal physiology of pedestrians in a Japanese city during summer.
• To analyze the impact of urban morphology on individual microclimates and physiological responses.
• To identify factors influencing sweating and skin temperature in response to thermal load.

Main Methods:

• Utilized a unique wearable system to measure ambient temperature, humidity, wind speed (U), and radiation (S and L).
• Recorded physiological data including skin temperature (T skin), pulse rate, and subjective thermal sensation.
• Employed a globe anemo-radiometer adapted for pedestrian use and monitored body motion.
• Subjects (26 healthy Japanese adults) traversed diverse urban routes, recording individual microclimate and responses.

Main Results:

• Pedestrian thermal environments varied significantly, differing from fixed-point data.
• Short-wave radiation (S) fluctuated due to sunlit/shade patterns in complex urban morphology.
• Low wind speed (U) in urban canyons was offset by enhanced convective heat exchange from movement, lowering T skin.
• Sweating increased with Standard Effective Temperature (SET*), showing clear gender (males > females) and body size (overweight > others) differences.
• T skin exhibited a linear relationship with SET* and varied by gender and body size, with higher sweating groups showing lower T skin due to evaporative cooling.

Conclusions:

• Wearable sensors provide crucial data on personal thermal exposure in dynamic urban settings.
• Urban morphology and pedestrian movement significantly influence individual thermal load and physiological responses.
• Gender and body size are key determinants of sweating rate and skin temperature regulation via evaporative cooling.