Air Quality in Selected Megacities

Abstract

About half of the world's population now lives in urban areas because of the opportunity for a better quality of life. Many of these urban centers are expanding rapidly, leading to the growth of megacities, which are often defined as metropolitan areas with populations exceeding 10 million inhabitants. These concentrations of people and activity are exerting increasing stress on the natural environment, with impacts at urban, regional and global levels. In recent decades, air pollution has become one of the most important problems of megacities. Initially, the main air pollutants of concern were sulfur compounds, which were generated mostly by burning coal. Today, photochemical smog-induced primarily from traffic, but also from industrial activities, power generation, and solvents-has become the main source of concern for air quality, while sulfur is still a major problem in many cities of the developing world. Air pollution has serious impacts on public health, causes urban and regional haze, and has the potential to contribute significantly to global climate change. Yet, with appropriate planning megacities can efficiently address their air quality problems through measures such as application of new emission control technologies and development of mass transit systems. This review is focused on nine urban centers, chosen as case studies to assess air quality from distinct perspectives: from cities in the industrialized nations to cities in the developing world. This review considers not only megacities, but also urban centers with somewhat smaller populations, for while each city-its problems, resources, and outlook-is unique, the need for a holistic approach to complex environmental problems is the same. There is no single strategy to reduce air pollution in megacities; a mix of policy measures will be needed to improve air quality. Experience shows that strong political will coupled with public dialogue is essential to effectively implement the regulations required to address air quality.

Megacities and Atmospheric Pollution

“…Zhang et al 57 showed a significant association of the air quality index with mortality, especially in the winter and among those 55 years and older with COPD and other respiratory diseases. Similar findings, reported by Chang et al, 58 showed an increase of ϳ20% in mortality from COPD for an SO 2 increase of 100 g/m 3 and of ϳ3% in respiratory deaths for a TSP increase of 100 g/m 3 . Xu et al 54 collected 1990 data from a communitybased hospital in Beijing to assess the association of air quality with daily nonsurgery outpatient visits, and found significant associations with both SO 2 and TSP levels.…”

“…A more detailed description of air quality management strategies applied in the nine case study cities is available as an online supplement to this review. 3 …”

The rise of low-cost sensing for managing air pollution in cities

“…Urban air quality is currently a global concern, which can be attributed to the massive scale of urbanisation and population growth, together with their resultant increases in traffic, industrialisation and energy use Molina et al 2004). It is understood that technological improvements in low emission motor engines have been offset by an exponential increase in vehicle numbers.…”

“…Although not relying on sensors, such a service is already in place in London through the airText programme (http://www.airtext.info/). There is no reason why similar sensor-based programmes cannot be launched in cities with high pollution levels, such as those in Asia Peng et al 2014) or elsewhere (Molina et al 2004). …”

“…Road vehicles are one of the major sources of outdoor air pollution in cities (Gurjar et al 2010;Kumar et al 2013;Molina et al 2004). At present, air pollution concentrations are collected by environmental or government authorities using networks of fixed monitoring stations, equipped with instruments specialised for measuring a number of pollutants, such as carbon monoxide (CO), nitrogen oxides (NOx), sulphur dioxide (SO 2 ), ozone (O 3 ) and particulate matter (PM).…”