I have now officially retired from the University and have stepped down as Head of the Particle Instruments Research Group that I founded in 1987. However, the Group remains very active under new leadership and I still contribute to its activities in the development of instrumentation and techniques for the detection, identification, and monitoring of airborne particles in atmospheric, environmental, occupational and security fields (see below). Having begun my academic career as a lecturer in Physics at Hertfordshire, I oversaw in the late 1980's the development of the Engineering Research and Development Centre. The ERDC grew throughout the 1990's, providing dedicated contract R&D support to industry and Government agencies as well as carrying out fundamental research in areas such as laser trapping of particles and microfluidic systems development. During this time, I and my research team pioneered several light scattering technologies that now form the basis of both research and commercial particle characterisation instruments used by atmospheric scientists, security agencies, and academic researchers in the UK, Europe, and USA. From 2002 to 2013 I was Director of the University's Science and Technology Research Institute one of three RI's that embraced all of the University's research activities. These Institutes have since been replaced with a new thematic research structure, as can be seen from the UH website http://www.herts.ac.uk/research.

Microparticle characterisation; aerosols; laser and optical instrumentation; light scattering.

My research activity has led to the development of numerous research instruments for airborne particle detection and characterisation, many of which are used by researchers around the world. For example:

• I led the development of a new generation of low-cost, high resolution, air quality sensors (product names: OPC-N3, OPC-R1) that since 2016 have been manufactured by Alphasense Ltd (Essex, UK; http://www.alphasense.com/index.php/air/) and have been sold into more than 70 countries worldwide. The sensors are designed for long-term unattended deployment and offer particle sizing from 0.3um to 40um (in the case of the OPC-N3). Unlike most OPCs, the N3 and R1 do not use a pump (and its required particle filter) to draw air through the sensor but a miniature low power fan.
• Variants of our SID (Small Ice Detector) and PPD (Particle Phase Discriminator) technology are now in use with atmospheric research organisations in the USA, Germany, Canada, as well as the UK. These instruments allow the detailed in situ analysis of ice crystal and aerosol particle morphologies, providing valuable on the cloud microphysical and radiative processes that underpin precipitation and climate. Our latest instrument, AIITS (Aerosol Ice Interface Transition Spectrometer) was developed under the NERC-funded CAST (Coordinated Airborne Studies in the Tropics)  for NASA'a Global Hawk atmospheric research unmanned aircraft and had its maiden flight in 2015.
• In the field of bio-aerosol detection, we have also developed the WIBS real-time biofluorescence sensor technology, now commericalized by DMT Inc., Boulder, USA, and these are being used in increasing numbers in national and international atmospheric research campaigns where a knowledge of the abundance, types, and dispersion of natural airborne biological particles such as pollens, bacteria and fungal spores, is required.
• Recent research projects included: the development of the world's first real-time asbestos fibre detector (see EU FP7 ALERT project), now being manufactured by Select Group Ltd, in the UK, and the development of low-cost particle monitors that formed part a large network of aerosol and gas sensors around Heathrow airport as part of the NERC-funded SNAQ project. (These monitors are now being manufactured by Alphasense Ltd in the UK as the OPC-N2 sensor).