case Studying air quality in Nanjing Nanjing China Share Sustainability Solutions to the lethal problem of poor air quality cannot be developed without accurate data. Vaisala and its partners are building the pilot of a completely new observation concept in Nanjing. The lethal problem of poor air quality needs to be addressed, but solutions to the problem are impossible to develop without comprehensive and accurate data. Vaisala and its partners are building a new network in Nanjing, aiming for a completely new observation concept. Vaisala, University of Helsinki, University of Nanjing, and the Finnish Meteorological Institute will build a dense air quality observation network in the megacity of Nanjing and the Yangtze River Delta in 2017–2019. The project’s main aim is to pilot a new, groundbreaking air quality pollution monitoring concept and to provide information for the research of air pollution phenomena—to understand better the chemical and physical processes of air quality formation and dispersion. Smog in Nanjing, China. Growing health problem Eventually, the results from this project can be used in improving air quality. The goal is to provide relevant information to citizens through e.g. mobile applications on the pollution levels in their neighborhood or route to work. Moreover, China is currently striving to curb the biggest industrial polluters, and the monitoring network may help pinpoint offenders. Air quality is a growing health problem around the world. More than 80% of people living in urban areas are exposed to air pollution levels exceeding WHO limits. According to the most recent WHO assessment, approximately 7 million people died prematurely because of air pollution in 2012. While all regions of the world are affected, people in densely populated and highly polluted megacities are impacted the most. Nanjing is an excellent choice for the new pilot network. The city of over six million inhabitants is located in one of China’s most industrialized areas, so it has major problems with air quality. It is also one of the most important centers for meteorological research in China, with long traditions in the University of Nanjing. Vertical Dimension into Consideration The Nanjing air quality monitoring network also aims at creating a completely new kind of concept for an air quality monitoring network, including vertical atmospheric profiling using LIDARs as well as multi-weather sensors for the first time at this scale in addition to air quality sensors. The combination will provide invaluable new information about air pollution and its movements. LIDARs are used to measure cloud height, but they can also be used to determine the mixing layer height, which is crucial in building a reliable model for air pollution dispersion and in numerical pollution simulations. Measuring the mixing layer is relevant, as it is where air pollutants are mostly created and spread. The layer height varies with location, season, time of day, weather, and pollutants. The thinner the mixing layer is, the higher the concentration of pollutants. Weather also affects air quality. Rain, for instance, can wash away air pollutants and so improve air quality momentarily. Wind, of course, can either bring in pollutants or remove them, depending on their source and its location.