2021, Ribeiro, Haroldo V., Oehlers, Milena, Moreno-Monroy, Ana I, Kropp, Jürgen P., Rybski, Diego

Urban scaling and Zipf’s law are two fundamental paradigms for the science of cities. These laws have mostly been investigated independently and are often perceived as disassociated matters. Here we present a large scale investigation about the connection between these two laws using population and GDP data from almost five thousand consistently-defined cities in 96 countries. We empirically demonstrate that both laws are tied to each other and derive an expression relating the urban scaling and Zipf exponents. This expression captures the average tendency of the empirical relation between both exponents, and simulations yield very similar results to the real data after accounting for random variations. We find that while the vast majority of countries exhibit increasing returns to scale of urban GDP, this effect is less pronounced in countries with fewer small cities and more metropolises (small Zipf exponent) than in countries with a more uneven number of small and large cities (large Zipf exponent). Our research puts forward the idea that urban scaling does not solely emerge from intra-city processes, as population distribution and scaling of urban GDP are correlated to each other.

2021, Meng, Xia, Liu, Cong, Chen, Renjie, Sera, Francesco, Vicedo-Cabrera, Ana Maria, Milojevic, Ai, Guo, Yuming, Tong, Shilu, Coelho, Micheline de Sousa Zanotti Stagliorio, Saldiva, Paulo Hilario Nascimento, Lavigne, Eric, Correa, Patricia Matus, Ortega, Nicolas Valdes, Osorio, Samuel, Garcia, null, Kyselý, Jan, Urban, Aleš, Orru, Hans, Maasikmets, Marek, Jaakkola, Jouni J. K., Ryti, Niilo, Huber, Veronika, Schneider, Alexandra, Katsouyanni, Klea, Analitis, Antonis, Hashizume, Masahiro, Honda, Yasushi, Ng, Chris Fook Sheng, Nunes, Baltazar, Teixeira, João Paulo, Holobaca, Iulian Horia, Fratianni, Simona, Kim, Ho, Tobias, Aurelio, Íñiguez, Carmen, Forsberg, Bertil, Åström, Christofer, Ragettli, Martina S., Guo, Yue-Liang Leon, Pan, Shih-Chun, Li, Shanshan, Bell, Michelle L., Zanobetti, Antonella, Schwartz, Joel, Wu, Tangchun, Gasparrini, Antonio, Kan, Haidong

Objective To evaluate the short term associations between nitrogen dioxide (NO2) and total, cardiovascular, and respiratory mortality across multiple countries/regions worldwide, using a uniform analytical protocol. Design Two stage, time series approach, with overdispersed generalised linear models and multilevel meta-analysis. Setting 398 cities in 22 low to high income countries/regions. Main outcome measures Daily deaths from total (62.8 million), cardiovascular (19.7 million), and respiratory (5.5 million) causes between 1973 and 2018. Results On average, a 10 μg/m3 increase in NO2 concentration on lag 1 day (previous day) was associated with 0.46% (95% confidence interval 0.36% to 0.57%), 0.37% (0.22% to 0.51%), and 0.47% (0.21% to 0.72%) increases in total, cardiovascular, and respiratory mortality, respectively. These associations remained robust after adjusting for co-pollutants (particulate matter with aerodynamic diameter ≤10 μm or ≤2.5 μm (PM10 and PM2.5, respectively), ozone, sulfur dioxide, and carbon monoxide). The pooled concentration-response curves for all three causes were almost linear without discernible thresholds. The proportion of deaths attributable to NO2 concentration above the counterfactual zero level was 1.23% (95% confidence interval 0.96% to 1.51%) across the 398 cities. Conclusions This multilocation study provides key evidence on the independent and linear associations between short term exposure to NO2 and increased risk of total, cardiovascular, and respiratory mortality, suggesting that health benefits would be achieved by tightening the guidelines and regulatory limits of NO2.