[7] His interests extend from source emissions, through atmospheric chemical and physical transformations,[8] to human exposures and effects upon health.

[9] His most significant work has been in the field of vehicle emitted particles, including their chemical composition and atmospheric processing.

[9][11][12] In addition to leading a large project on diesel exhaust particles, he is also engaged in major collaborative studies of processes determining air quality in Beijing and Delhi.

He was appointed Order of the British Empire OBE in the 2004 New Year Honours for services to environmental science[13] and elected a Fellow of the Royal Society (FRS) in 2017.

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