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Urban heat waves pose a significant risk to the health and safety of city dwellers, with urbanization potentially amplifying the health impact of extreme heat. Accurate assessments of population heat exposure hinge on the interplay between temperature, population spatial dynamics, and the epidemiological effects of temperature on health. Yet, many past studies have over-simplified the matter by assuming static populations, leading to substantial inaccuracies in heat exposure assessments. To address these issues, this study integrates dynamic population data, fluctuating temperature, and the exposure-response relationship between temperature and health to construct an advanced heat exposure assessment framework predicated on a population dynamic model. We analyzed urban heat island characteristics, population dynamics, and heat exposure during heat wave conditions in Beijing, a major city in China. Our findings highlight significant intra-day population movement between urban and suburban areas during heat wave conditions, with spatial population flow patterns showing clear scale-dependent characteristics. These population flow dynamics intensify heat exposure levels, and the disparity between dynamic population-weighted temperature and average temperature is most pronounced at night. Our research provides a more comprehensive understanding of real urban population heat exposure levels and can furnish city administrators with more scientifically rigorous evidence. [Display omitted] • Urban heat waves pose a significant risk to the health and safety of city dwellers • Population movement between urban and suburban areas is obvious in megacities • Movement of people between places of work and residence modifies the heat exposure • A dynamic population risk assessment index for heat exposure was developed [ABSTRACT FROM AUTHOR]

Volatile organic compounds (VOCs) play key roles in the formation of particulate matter (PM) and oxidants and hence enhance the summertime air pollution. With data analysis from various field observations (urban station: Haidian, HD; suburb station: Changping, CP; regional background station: Shangdianzi, SDZ) in June 2011, we found that the mean O 3 concentrations throughout the observation period can be arranged in order: SDZ＞CP＞HD. The mean PM concentrations can be arranged in order: HD＞CP＞SDZ. The mean concentration of total VOCs at HD was close to that at CP, but much higher than that at SDZ. Oxygenated volatile organic compounds (OVOCs) made the largest portion of VOCs (~40%) at the three stations, followed by alkanes and alkenes. Good positive correlations between the concentrations of PM and O x (=O 3 ＋NO 2) at high air temperature (≥30 °C at HD and CP; ≥28 °C at SDZ) and low RH (≤60%) were found in the daytime (07:00–18:00 LT). However, the PM concentrations were partly negatively correlated with O x at lower temperatures (≤26 °C at HD and CP; ≤22 °C at SDZ) and higher RH (≥80%). The PM concentrations were found either positively (HD and CP) or negatively (SDZ) correlated with aromatics at high temperature and low RH. The aging degree of air masses at the three stations can be arranged in order: SDZ＞CP＞HD. This can qualitatively explain the different PM−aromatics correlations. Our data suggested the other groups of VOCs may promote the increase of PM concentrations unless the PM levels become higher than 140 μg m−3 under humid conditions. This study confirms the importance of VOCs in the formation of summertime PM and oxidants over Beijing. Image 1 • Parallel photochemical formations of PM and O 3 caused positive PM-O x correlations. • Positive PM-aromatics correlations were found at HD and CP, but negative at SDZ. • OVOCs made the largest portion of VOCs (~40%) in the high ozone episode. • VOCs may promote the increase of summertime PM concentrations under humid conditions. [ABSTRACT FROM AUTHOR]

The effect of temperature on cardiovascular disease (CVD) mortality has been extensively studied. However, it remains largely unknown over whether there is any difference between urban and suburban areas within the same city and how urbanization modifies the relationship between temperature and CVD mortality. In order to examine whether the association between temperature and CVD mortality existed difference in urban and suburban areas, and how urbanization modified this association, we used a distributed lag nonlinear model and a generalized additive model to investigate temperature-related CVD mortality in urban and suburban areas in Beijing, China, from 2006 to 2011. The age, gender, and educational attainment of the population were stratified to explore the modifying effect. We observed that the impacts of heat and cold temperature on CVD mortality were higher in suburban areas than in urban areas. In addition, the elderly and illiterate subjects in suburban areas were more vulnerable to both heat and cold than their counterparts in urban areas. Moreover, higher urbanization levels were significantly associated with districts having lower the excess risks for temperature- CVD mortality. Our findings provide evidence that populations in suburban Beijing have higher risk of temperature-related CVD mortality than those in urban areas. Therefore, greater attention should be paid to vulnerable groups in suburban areas to reduce temperature-related health burden. • Urban/suburban temperature-effect differences on mortality were compared. • Urbanization modifies the relationship between temperature and CVD mortality. • People living in suburban areas were more vulnerable to both hot and cold temperatures. • CVD mortality varied with age, gender, and educational attainment in both urban and suburban areas. • Implies different patterns of temperature impact between developed and developing countries. [ABSTRACT FROM AUTHOR]