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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]

In this study, hourly and daily records since 2005 and correlation, regression and composite methods were used to analyze the long-term evolution of surface O 3 and PM 2.5 concentrations at the rural station of Shangdianzi (SDZ) and urban station of Baolian (BL) over Beijing and their relationships with meteorological conditions. The results show that the mean concentrations of PM 2.5 (O 3 ) decreased (increased) at the urban and rural stations over the last decade. The linear trends of the annual mean concentrations of PM 2.5 at BL and SDZ were −31.8 ug/m 3 /10yr (−4.3%/yr) (p < 0.01) and −13.3 ug/m 3 /10yr (−2.9%/yr) (p < 0.05), respectively. In winter, the mean wind speed ( W s ) and relative humidity ( RH ) were the most closely correlated with O 3 at both stations, whereas RH and sunshine hours ( S ) were most closely correlated with PM 2.5 . The correlation coefficients and explained variances in spring and autumn were generally less than those in winter and greater than those in summer. Moreover, increase in precipitation can significantly reduce the PM 2.5 concentration in both urban and rural areas in Beijing, whereas trace and light precipitation more effectively decreases the O 3 concentration. Concentrations of PM 2.5 (O 3 ) on haze days increased by 114% (3%) and 162% (20%) compared with that on non-haze days at the urban and rural stations, respectively. This result suggests that haze is a major manifestation of air pollution in Beijing. [ABSTRACT FROM AUTHOR]

Abstract: Measurements of aerosol scattering coefficient (σsp) and PM2.5 concentration obtained during June 2008 to May 2009 at urban, suburban, and rural sites in Beijing area. The mean value of σsp during measurement period was 301±307, 263±263, 182±201Mm−1 at Baolian (BL: urban site), Changping (CP: suburban site) and Shangdianzi (SDZ: rural site), respectively. The seasonal and diurnal patterns of σsp were analyzed with the measurement data. The σsp showed different seasonal and diurnal patterns at these three sites. The seasonal fluctuations inσsp in urban area were mostly influenced by seasonal variability in both emissions and meteorological conditions, while the seasonal wind patterns seemed to dominate the σsp in the suburban and rural areas. The diurnal activity of σsp generally showed a bimodal, trimodal and a unimodal pattern at BL, CP and SDZ sites, respectively. The diurnal variation of boundary layer height companying with source activity was mainly dominated the diurnal variation of σsp at urban and suburban sites. The mountain-valley breeze and boundary layer growth in SDZ region mostly dominated the diurnal variation of σsp. The mass scattering efficiency of PM2.5 was estimated at BL and SDZ, which showed a decreasing trend from urban to rural site with different seasonal variation at two sites. During fog and haze episodes, the lower northeasterly winds could result in significant spatial difference in σsp, while the σsp was spatially uniform under the influence of stronger southerly winds. [Copyright &y& Elsevier]

Abstract: In China, visibility condition has become an important issue that concerns both society and the scientific community. In order to study visibility condition trends and characteristics for the BTH (Beijing, Tianjin, and Hebei) area, meteorological data (1980–2008) were collected from over 100 ground stations. The 29-year average visibilities were 21.7, 13.6, and 18.0km for Beijing, Tianjin, and Hebei, respectively, and the long-term visibility of BTH exhibited decreasing trend before 1998, slight fluctuations between 1998 and 2006, and increasing trend between 2006 and 2008. Most of the visibility trend lines depicted the same fluctuations and converged to a very narrow range for the urban stations in each area. Average visibility at non-urban stations was apparently higher than that at urban stations, with 29-year average of 19.4 and 14.4km respectively. Visibility was higher in the spring and autumn for Tianjin and Hebei, but best in the winter for Beijing probably due to higher wind speed and lower relative humidity. The visibility spatial distribution showed lower visibility that primarily occurred in the urban areas of Beijing, Tianjin, and Shijiazhuang. The trends regarding days with haze, good visibility, and fog for the urban and non-urban areas of the BTH region were also discussed. There was an increasing trend for days with haze but no apparent trend for days with good visibility. On average, there were no more than nine foggy days per year in the BTH area. Visibility and PM2.5 were observed to negatively correlate at two stations in Beijing, where PM2.5 data are available, and aerosols could cause a greater degree of visibility impairment in the summer months according to the correlations between visibility and PM2.5 concentration. [Copyright &y& Elsevier]

Three years of measurement of PM2.5 with 5-min time resolution was conducted from 2005 to 2007 in urban and rural environments in Beijing to study the seasonal and diurnal variations in PM2.5 concentration. Pronounced seasonal variation was observed in the urban area, with the highest concentrations typically observed in the winter and the lowest concentrations generally found in the summer. In the rural area, the maximum in PM2.5 concentration usually appeared during the spring, followed by a second maximum in the summer, while the minimum generally occurred in the winter. Significant diurnal variations in PM2.5 concentration were observed in both urban and rural areas. In the urban area, the PM2.5 concentration displays a bimodal pattern, with peaks between 7:00 and 8:00 a.m. and between 7:00 and 11:00 p.m. The minimum generally appears around noon. The morning peak is attributed to enhanced anthropogenic activity during rush hours. The decreases of boundary layer height and wind speed in the afternoon companying with increased source activity during the afternoon rush hour result in the highest PM2.5 concentration during evening hours. In the rural area, the PM2.5 concentration shows a unimodal pattern with a significant peak between 5:00 and 11:00 p.m. The seasonal and diurnal variations in PM2.5 concentration in the urban area are mostly dominated by the seasonal and diurnal variability of boundary layer and source emissions. The year-to-year variability of rainfall also has an important influence on the seasonal variation of PM2.5 in the urban area. The seasonal and diurnal wind patterns are more important factors for PM2.5 variation in the rural area. Southerly winds carry pollutants emitted in southern urban areas northward and significantly enhance the PM2.5 concentration level in the rural area. [Copyright &y& Elsevier]

Worldwide epidemiological studies have demonstrated that short-term associations of particulate matter (PM), might be further complicated by ambient temperatures, and increase human mortality. In China, among various PM indices, the health effects of black carbon (BC) are less understood due to the lack of data availability. Additionally, it is unclear how temperature modifies simultaneous and adverse effects of BC, and fine (PM size <2.5 μm; PM 2.5), and coarse particles (PM 2.5-10), on mortality outcomes. We adopted time-series Poisson generalized additive models to investigate temperature modifying effects on the association between three different PMs (BC, PM 2.5 , and PM 2.5-10) and mortality (non-accidental, respiratory and cardiovascular mortality) in Beijing, China, from 2010 to 2016. Average daily BC, PM 2.5 , and PM 2.5-10 concentrations were 4.95, 72.3, and 52.1 μg/m3, respectively, which were all significantly associated with daily mortality. High temperature strongly amplified effects of BC, PM 2.5 , and PM 2.5-10 on human mortality, especially BC effects that were most pronounced at >28 °C. Harmful effects were estimated for increases in non-accidental, respiratory, and cardiovascular mortality per interquartile increments in BC (4.11 μg/m3), PM 2.5 (62.37 μg/m3), and PM 2.5-10 (46.71 μg/m3) concentrations from the moving average of current and previous day (lag01) under high temperature (>28 °C). Mortality increases in non-accidental, respiratory, and cardiovascular categories were 5.12% (95% confidence interval [CI]: 4.79, 5.45), 7.41% (95%CI: 6.42, 8.40), and 6.36% (95%CI: 2.45, 10.3) for BC; 3.85% (95%CI: 3.27, 4.43), 6.64% (95%CI: 5.63, 7.65), and 4.54% (95%CI: 3.31, 5.78) for PM 2.5 ; and 2.56% (95%CI: 1.45, 3.67), 3.41% (95%CI: 1.53, 5.29), and 3.19% (95%CI: 2.44, 3.94), for PM 2.5-10 , respectively. These findings suggest that controlling the emission of ambient particles, especially BC, and improving air quality during summer would substantially benefit population health. Furthermore, BC should be considered as a crucial air quality indicator to reflect PM health risk. Image 1 • To test the synergistic effects of temperature and black carbon (BC) on mortality. • High temperature amplified the harmful effects of BC and PM on mortality. • The modifying effects of temperature on BC were different from that on PMs. [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]

Urban agglomerations are considered as significant space typologies in the post globalization & digitalization era. The spatial linkage intensity of cities in urban agglomeration is an important basis for evaluating the development and compactness of urban agglomerations. The requirements associated with the major national strategy to achieve the coordinated development of the Beijing-Tianjin-Hebei (BTH) region and the research methods made possible by Big Data in the Internet era have created the realistic possibility of revealing the strength of spatial networks and the spatial differentiation rules of urban agglomerations. This study uses Web Crawler to obtain 500,000 sets of Weibo data in 13 cities of the BTH urban agglomeration. Three criteria and nine indicators are used to construct an index system and a model to quantitatively evaluate the strength of spatial networks in the BTH urban agglomeration. The results show that spatial network connections between cities in the urban agglomeration are not strong overall, reflecting the limited development of urban agglomeration; the spatial networks in the urban agglomeration have hierarchical and centralized characteristics, which reflect the imbalanced development of the city network; Beijing, Tianjin, and Shijiazhuang are the centers of the social network connections in the BTH urban agglomeration, which means that Weibo's online space reinforces the existing urban system; there is a positive correlation between network spatial connectivity and the hierarchy of cities in the urban agglomeration, where cities with higher levels would have more urban network connections; Generally, Weibo network connections are stronger than economic or transport links between the cities, and the development of information technology may reduce the disparity of regional development. This research innovatively uses social network big data to reveal the strength of spatial network connections and spatial differentiation rules in the urban agglomeration. The methodology provided in this paper is systematic enough for generalization. • The spatial linkage intensity is an important basis for evaluating the development and compactness of urban agglomerations. • We construct a new index system using network big data to measure the strength of connection between cities. • The methodology can be applied to other regions when examining social network big data from Facebook or Twitter. [ABSTRACT FROM AUTHOR]

Surface particulate matter with an aerodynamic diameter of <2.5 μm (PM2.5) and column-integrated aerosol optical depth (AOD) exhibits substantial diurnal, daily, and yearly variabilities that are regionally dependent. The diversity of these temporal variabilities in urban and rural areas may imply the inherent mechanisms. A novel time-series analysis tool developed by Facebook, Prophet, is used to investigate the holiday, seasonal, and inter-annual patterns of PM2.5 and AOD at a rural station (RU) and an urban station (UR) in Beijing. PM2.5 shows a coherent decreasing tendency at both stations during 2014–2018, consistent with the implementation of the air pollution action plan at the end of 2013. RU is characterized by similar seasonal variations of AOD and PM2.5, with the lowest values in winter and the highest in summer, which is opposite that at UR with maximum AOD, but minimum PM2.5 in summer and minimum AOD, but maximum PM2.5 in winter. During the National Day holiday (1–7 October), both AOD and PM2.5 holiday components regularly shift from negative to positive departures, and the turning point generally occurs on October 4. AODs at both stations steadily increase throughout the daytime, which is most striking in winter. A morning rush hour peak of PM2.5 (7:00–9:00 local standard time (LST)) and a second peak at night (23:00 LST) are observed at UR. PM2.5 at RU often reaches minima (maxima) at around 12:00 LST (19:00 LST), about four hours later (earlier) than UR. The ratio of PM2.5 to AOD (η) shows a decreasing tendency at both stations in the last four years, indicating a profound impact of the air quality control program. η at RU always begins to increase about 1–2 h earlier than that at UR during the daytime. Large spatial and temporal variations of η suggest that caution should be observed in the estimation of PM2.5 from AOD. [ABSTRACT FROM AUTHOR]

Due to its twofold effects on climate change and air quality, black carbon (BC) is of wide concern in the atmospheric sciences. Considerable uncertainty exists as to the health effects of atmospheric BC for the limited epidemiological and toxicological studies. As combustion-derived BC is one important component of PM 2.5 (particles with aerodynamic diameters less than 2.5 μm), the question remains of whether or not BC may play an important role in PM 2.5 -related health risks. To quantitatively analyze the short-term health effects of BC and PM 2.5 , a confounder-adjusted semi-parametric generalized additive model (GAM) of a time series study was used to calculate the concentration-response relationship between BC and PM 2.5 and daily cardiovascular disease (CVD) mortality from 2006 to 2011 in Beijing. During the study period, the mean daily concentrations of BC and PM 2.5 were 6.8 μg/m3 and 75.9 μg/m3, respectively. The results showed that BC was significantly associated with CVD mortality, and an interquartile range (IQR) increase in BC (5.7 μg/m3) and PM 2.5 (64. 5 μg/m3) were associated with 2.70% (95% CI: 2.20, 3.21) and 4.06% (95% CI: 3.47, 4.65) increase in CVD mortality. The health risk associated with BC may less than that of PM 2.5. When adjusted for nitrogen dioxide (NO 2) and sulfur dioxide (SO 2), the effects of BC remained statistically significant. It showed the relatively difference between BC and PM 2.5 when it comes to the modification effects of age, gender and educational attainment. These findings provide valuable evidence to the rare studies of the concentration-response relationship of BC with human health in developing countries. Image 1 • Few studies in Asian developing countries have examined the health effects of BC. • We observed significant associations of BC and PM 2.5 with daily cardiovascular mortality in Beijing. • The health risk associated with ambient BC may less than that of PM 2.5. [ABSTRACT FROM AUTHOR]

Visibility can be used as a highly relevant visual indicator of the air pollution level. Published data on the correlations between visibility and health outcomes are very limited in China, and the health effects of slight haze on the human body have not been clarified. A semi-parametric generalized additive model (GAM) was used to assess the acute health effects of visibility on respiratory–cardiovascular mortality in Beijing, China. The correlation between visibility and PM 2.5 as well as the contributions of PM 2.5 to the health effects of visibility were analysed. Stratification model was employed to investigate the health effects of slight haze. The mortality risk of impaired visibility on the current exposure day peaked and was statistically significant for all the mortality outcomes. Every 1 km decrease in visibility corresponded to a 0.78% (95% CI: 0.62–0.95%) increase in total respiratory mortality and 0.54% (95% CI: 0.45–0.61%) increase in total cardiovascular mortality. Older people (age ≥65) were at a higher risk than the younger age group under impaired visibility. PM 2.5 had a negative logarithmic relationship relative to visibility. After adjustment for PM 2.5 , the risk estimates for both respiratory and cardiovascular mortality reduced. Short-term exposure to low visibility was significantly associated with increased respiratory and cardiovascular mortality in Beijing. The health risk of impaired visibility was particularly high, even in slight haze. The hazardous effects of visibility can be partially attributed to the effects of PM 2.5. These results can provide useful reference for relevant agencies to determine whether an adjustment to the haze warning level is warranted. Our findings indicate that visibility can be used as an alternative indicator for air quality assessments if air pollution data are insufficient or not available, particularly in developing countries. Image 1 • Studies on association between visibility and health outcomes are rare in China. • Exposure to impaired visibility is significantly related to increased mortality. • Health effects of impaired visibility can be partially explained by PM 2.5. • Health risk of impaired visibility is intense, even in slight haze. [ABSTRACT FROM AUTHOR]

Daily PM 2.5 samples were collected at an urban site in Beijing during four one-month periods in 2009–2010, with each period in a different season. Samples were subject to chemical analysis for various chemical components including major water-soluble ions, organic carbon (OC) and water-soluble organic carbon (WSOC), element carbon (EC), trace elements, anhydrosugar levoglucosan (LG), and mannosan (MN). Three sets of source profiles of PM 2.5 were first identified through positive matrix factorization (PMF) analysis using single or combined biomass tracers — non-sea salt potassium (nss-K + ), LG, and a combination of nss-K + and LG. The six major source factors of PM 2.5 included secondary inorganic aerosol, industrial pollution, soil dust, biomass burning, traffic emission, and coal burning, which were estimated to contribute 31 ± 37%, 39 ± 28%, 14 ± 14%, 7 ± 7%, 5 ± 6%, and 4 ± 8%, respectively, to PM 2.5 mass if using the nss-K + source profiles, 22 ± 19%, 29 ± 17%, 20 ± 20%, 13 ± 13%, 12 ± 10%, and 4 ± 6%, respectively, if using the LG source profiles, and 21 ± 17%, 31 ± 18%, 19 ± 19%, 11 ± 12%, 14 ± 11%, and 4 ± 6%, respectively, if using the combined nss-K + and LG source profiles. The uncertainties in the estimation of biomass burning contributions to WSOC due to the different choices of biomass burning tracers were around 3% annually and up to 24% seasonally in terms of absolute percentage contributions, or on a factor of 1.7 annually and up to a factor of 3.3 seasonally in terms of the actual concentrations. The uncertainty from the major source (e.g. industrial pollution) was on a factor of 1.9 annually and up to a factor of 2.5 seasonally in the estimated WSOC concentrations. [ABSTRACT FROM AUTHOR]

Black carbon (BC) and its mixing state were measured with a ground-based single particle soot photometer in urban Beijing during the extremely polluted winter of 2013. Up to 70 ± 14% of the BC-containing particles were thickly-coated during periods of haze, compared to 37 ± 9% on non-hazy days. The thickly-coated number fraction (NF BC-thick ) increased with increasing BC, reaching a plateau at ∼80–90% when BC concentrations were ≥15 μg m −3 and visibility was ≤2 km. Regional inflows brought more aged, highly thickly-coated BC to Beijing during haze. The absorption coefficient showed a distinct linear correlation with BC concentration; the mass absorption efficiency (MAE) of BC was acquired, with an overall mean of 4.2 ± 0.01 m 2 g −1 at 870 nm. The MAE of BC amplified with increasing ambient relative humidity. This was largely explained by the increase in NF BC-thick , which was likely due to the enhanced production of secondary aerosol 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]