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Cities face twin challenges of changing climate and urban heat island (UHI) effect, with the environmental implications of urbanization still unclear. This study employs the Weather Research and Forecasting (WRF) model to examine the impacts of urbanization in the Greater Bay Area (GBA) during warm and cold seasons in past (2000) and near-future (2030) scenarios [i.e., under shared socioeconomic pathways (SSP): SSP1-26, SSP2-45, and SSP5-85]. Datasets from the World Urban Database and Access Portal Tools (WUDAPT) were incorporated into the WRF model to improve the representation of urbanization effects on weather patterns. Our findings indicate that urban expansion significantly increases urban temperatures and decreases wind speed across selected climate change scenarios. The spatially averaged urban temperatures in the fine resolution domain for 2030 could rise by 0.9 °C (warm season) and 2.4 °C (cold season), respectively, and urban wind speed decreases by ∼ 3 m/s under the SSP5-85 scenario. In cold season, the UHI effect could last over 20 h, while urban area may experience cooler nighttime temperatures than rural areas in warm season. Moreover, the future scenario predicts higher daytime O 3 levels due to the warming effects of climate change and urbanization, but lower nighttime levels in warm season, attributed to intensified south-easterly sea breeze and background winds, when compared to the past scenario. This study highlights the importance of incorporating urbanization and climate change in future urban atmospheric environment studies, and underscores that urban climate change adaptation and mitigation should consider extra impacts on built-environment caused by urbanization. • Climate change and urbanization impacts on meteorological and O 3 fields were explored in GBA. • Urbanization and climate change are expected to raised temperatures by 0.9 °C in warm season over the study area. • Urbanization and climate change are expected to raised temperatures by 2.4 °C in cold season over the study area. • Urbanization is expected to reduce wind speed by 3 m/s and intensify sea breeze penetration over the study area. [ABSTRACT FROM AUTHOR]

Efforts to enhance greenhouse gas (GHG) emission reduction in East Asia play a pivotal role on both global and regional scales in advancing climate mitigation strategies. This study aimed to better constrain anthropogenic CO 2 emission estimates by expanding the network of near-surface in-situ stations for CO 2 observations across South Korea. To achieve an optimal CO 2 network design, we conducted an Observing System Simulation Experiment (OSSE) coupled with the Stochastic Lagrangian Transport model (STILT), utilizing meteorological data from the Korean Integrated Model (KIM). Our inversion setup incorporated two CO 2 emission datasets with a 0.1o resolution: EDGAR v6 for prior emissions and GRACED for truth emissions. A uniform model-mismatch error of 3 ppm was introduced across sites. The effectiveness of the existing five in-situ stations, termed the base network, in South Korea was evaluated to gauge their ability to constrain CO 2 surface flux estimates. However, the findings revealed a reduction in flux uncertainty of only 29.2%, which fell short of the desired uncertainty reduction goal. In this base network, the Lotte World Tower (LWT: 37.5126°E, 127.1025°E) in Seoul and the Anmyeondo (AMY: 36.538576° N, 126.330071° E) site in Taean county stood as major contributors, with estimated reductions of 17.48% and 6.35%, respectively. Consequently, we proposed and developed an extended network, identifying seven candidate sites based on consideration of logistical factors, existing infrastructures, and proximity to the emission source regions. An incremental optimization scheme ranked their contributions, resulting in an additional 25% reduction, bringing the total to 54.13%. However, it is noteworthy that diminishing returns (ranging from 13% to less than 0.1%) were observed with an increase in station count mainly due to the possibility that adding a station earlier in the sequence might render subsequent stations redundant. Despite this, the proposed CO 2 network successfully reduced uncertainty in emissions, narrowing the gap with the objectives of the Global Greenhouse Gas Watch (G3W). • Designing CO 2 near-surface observation network over South Korea. • New stations selected considering logistic factors, existing infrastructures, and proximity to emission sources. • The base network was able to reduce 29.18% of the uncertainty in CO 2 emissions. • Extending network, by adding new seven candidate sites, led to a total uncertainty reduction of 54.13%. [ABSTRACT FROM AUTHOR]

Hong Kong has used a risk-based Air Quality Health Index (AQHI) system for nearly a decade, which aggregates hospitalization risks associated with short-term exposure to pollutants. Serving as an air pollution risk communication tool, it keeps the public informed about the current air quality, anchoring around the World Health Organization's (WHO) 2005 Air Quality Guidelines (AQGs). Given the WHO's recent update to the AQGs in 2021, it is pertinent to examine how Hong Kong's air quality risk communication might be enhanced using these updated guidelines. The AQHI currently focuses only on short-term health risks, potentially leading to an underestimation of cumulative impacts. To address this, we propose enhancing the AQHI to include both long-term and short-term health risks. Short-term risks are estimated based on excess hospitalization risks from various pollutants using local data, while long-term risks are estimated using beta coefficients from the WHO due to limited local data. We further suggest using the WHO's Interim Targets (ITs) as thresholds for health risk categories, eliminating arbitrary cut-points. Promoting both public health protection and climate mitigation is important but challenging, particularly with the surge in ozone levels due to enhanced NOx controls in VOC-limited regions like Hong Kong and Guangdong. Nevertheless, despite the rise in ozone, combined health risks in these areas have decreased due to reductions in NO 2 and PM concentrations. Shifting to an AQHI-like total health risk assessment emphasizes the harmonization of health protection and climate mitigation goals. This health-focused framework posits that rigorous NOx controls can effectively serve both policy objectives in tandem. • After a decade's review, HK's AQHI advised to report on long-term health risks. • Original short-term AQHI helps daily plans but may overlook crucial long-term risks. • Long-term health risk-based AQHI clarifies air quality trends for easier public grasp. • Aligning AQHI bands with WHO AQGs & ITs ensures clear, transparent risk communication. • Drastic fossil fuel cuts boost health, aid climate, despite temporary ozone rise. [ABSTRACT FROM AUTHOR]