Quantifying feedbacks between pollution smog, radiation and dynamics in a polluted megacity

Poor air quality has a major impact on millions of people living in very large conurbations, commonly known as megacities. In such cities, pollution levels can be very high and be one of, if not the major public health problem. One such city Beijing, which is a megacity of over 21 million inhabitants, is subjected to pollution from a wide range of sources. Pollutants accumulate under stagnant weather conditions in winter-time as a result of poor mixing and a persistent haze or fog leads to major air quality exceedances and human health impacts. Characterising these processes is an important part of developing strategies to control and mitigate pollution in the region. The Centre for Atmospheric Science is part of a large UK-China AIR Pollution and Human Health programme, a significant part of which is to understand and quantify the major sources of particle pollution and the main atmospheric processes exacerbating the effects. This PhD will directly contribute to these larger project goals.

Pollution events are often at their most severe during stagnant conditions, when a strong inversion at the top of the surface layer of the atmosphere inhibits mixing and dilution. Pollution particles take up water when exposed to increased humidity, as may happen when they are lifted from the surface to the top of the surface layer, and if the humidity is sufficiently high then a fog may form. This haze or fog causes a greater amount of incoming sunlight to be scattered back to space and an increased emission of heat upwards from the fog top leading to cooling of the surface layer and strengthening of the inversion exacerbating the pollution event. A regional modelling study over Beijing has shown that haze can have a substantial impact on the radiation balance of the lower atmosphere and hence on boundary layer dynamics, which in turn influences the haze itself. However, to date simulations of these feedbacks have not been directly tested against observations, nor has their contribution to sustaining and enhancing pollution episodes been quantified.

During the PhD you will characterise the relationships between the chemical and physical properties of the pollution particles, their hygroscopic properties and their ability to act as cloud condensation nuclei. A range of models are available, including box models carrying detailed aerosol physical and chemical processes including interactions with water; a large eddy model capable of simulate boundary layer dynamical processes and their link to radiation and a regional air quality model. You will use a selection of these models to explore the partitioning of components between the gas and particle phases as the air is lifted from the surface and so examine the extent to which pollution interacts with radiation and feeds back on the dynamics of the polluted surface layer. The large data set generated by the wider programme includes multi-height measurements on a tall tower as well as surface based remote sensing of boundary layer properties. These data will be available to be used to initialise and constrain the simulations to explore the extent to which these feedbacks exacerbate air quality in megacities such as Beijing. You will be expected to take part in the two major field experiments will take place in winter 2016/7 and summer 2017 in Beijing.

Enquiries
Professor Hugh Coe
[Email Address Removed]

Centre for Atmospheric Sciences
School of Earth, Atmospheric and Environmental Sciences
Simon Building
University of Manchester
Oxford Road, Manchester
M13 9PL