Quantifying Regional Aerosol Sources Using Space-Borne Observations of Aerosol Optical Properties

CASE PhD Studentship supervised by Paul Palmer

Introduction to the Science Problem:

Atmospheric aerosols are tiny particles suspended in the air. Their atmospheric abundance has serious implications for climate, air pollution, and human health. The largest man-made source is from the burning of fossil fuels (cars, power plants), while natural sources include desert dust, volcanoes, forest fires, and sea spray. The main sinks of aerosols include gravitational settling and scavenging due to rain, leading to atmospheric lifetimes of typically a few days. Despite their short lifetime they affect climate in a number of direct and indirect ways:

  • Aerosols can reflect or absorb radiation at different wavelengths, depending on their size and composition.
  • Man-made aerosols, by providing elevated levels of particles that act as seeds for water droplets, can increase the lifetime and reflectivity of clouds.
  • Aerosols provide additional surfaces on which heterogeneous chemistry can occur thereby altering the chemical, and consequently radiative, properties of the atmosphere.

The short lifetimes of atmospheric aerosols, and consequent large spatial variations, make it difficult to relate ground-based observations to regional spatial scales. Our poor understanding of the composition and distribution of atmospheric aerosols on a global scales is recognized by the international climate community as one of the largest uncertainties in our current understanding Earth's climate

 

Figure: Aerosol pollution over Northern India and Bangladesh. This true-color image was acquired on December 4, 2001, by the Moderate-resolution Imaging Spectroradiometer (MODIS), flying aboard NASA’s Terra satellite.

Project Outline:

New satellite observations of aerosol optical properties, interpreted using a global 3-D model of atmospheric composition, provide an unprecedented opportunity to understand and quantify the sources, sink and chemical processing of different aerosols. Currently there are several Earth-observing satellite instruments that provide aerosol optical depths (AODs) derived from radiance measurements.

We will initially focus on data from MODIS (Figure), a NASA instrument aboard the Terra and Aqua satellite platforms. Correlative trace gas data measured by other satellite instruments in similar orbits (e.g., carbon monoxide from TES) provide additional observation constraints on the regional source attribution of atmospheric aerosols. As the project progresses we will conduct a similar analysis with AOD data from the European ATSR2 (ERS-2) and AATSR (Envisat) satellite instruments and correlative trace gas measurements from the instruments on the Envisat or MetOp satellites.

We will use the new TOMCAT/UKCA global 3-D model of tropospheric composition, developed by Dr Graham Mann and Professors Ken Carslaw and Martyn Chipperfield, to interpret satellite observations of AOD and correlative trace gases. The model will provide information about the sensitivity of the satellite data to particular aerosol sources from different geographical regions. The sensitivity information will be used to help relate the AOD and correlative trace gas measurements to regional aerosol emissions.

The successful candidate will be based at the University of Leeds, supervised by Dr Paul Palmer. The PhD studentship is funded by the NERC Data Assimilation Research Centre, a NERC Centre of Excellence. CASE sponsorship is from the Rutherford Appleton Laboratory.