Special issue  

Rapid population growth and urbanization worldwide accelerate eco-environmental and socio-economic stress as well as adverse climatic and health impacts on urban dwellers. Atmospheric modelling research has largely been performed on a horizontal grid spacing of kilometres or larger due to a lack of understanding of the local-scale phenomena, appropriate parameterizations, and adequate modelling tools and computer resources. Urban- to hyperlocal-scale (at street or city block level) air pollution, climate change, and their impacts on population exposure and human health have increasingly received attention from both researchers and policy makers around the world. Several state-of-the-science models have recently been developed for urban- to hyperlocal-scale air pollution modelling, including the street-network model, the Model of Urban Network of Intersecting Canyons and Highways (MUNICH) that incorporates detailed representations of gas-phase chemistry and secondary aerosol formation pathways, and the Street-in-Grid (SinG) model that dynamically combines a 3-D Eulerian chemical–transport model (CTM), Polair3D, with MUNICH. There have been increasing numbers of developers and users for MUNICH, SinG, and other similar coupled 3-D CTMs and urban canyon models for street-level air pollution modelling worldwide, such as CALIOPE-Urban, the Operational Street Pollution Model (OSPM) coupled with the Danish Eulerian Hemispheric Model (DEHM), and the Parallelized Large-Eddy Simulation Model (PALM). Meanwhile, air quality measurement data at hyperlocal scales have become increasingly available for model validation and improvement. Recognizing the urgent need for scientific advancement, pollution and exposure assessment, policy making, and public health protection at urban to hyperlocal scales, we launched a special issue on air quality research at street level in 2018, in which we have published 20 journal papers: https://acp.copernicus.org/articles/special_issue994.html. This special issue (Part II) will continue to advance scientific understanding of local-scale atmospheric phenomena, promote discussion on state-of-the-science urban as well as hyperlocal street- and city-block-level air quality research including measurements, emissions, and model development, and encourage application for complex interactions among urban air pollution, climate, and health. The special issue (Part II) is open for all submissions which address the following themes.

• 3-D Street-in-Grid (SinG) model development and application
• Urban canyon and network model development and its incorporation into 3-D CTMs
• Urban and street-level air quality modelling in support of human exposure assessment
• Impact of urban traffic emissions on air quality and human health at a street level
• Hyperlocal (street and city block scales) air quality measurement and modelling
• Urban infrastructure-induced circulation and its impact on city planning