Black carbon flux measurements in megacities using the eddy covariance method.

Abstract

Black Carbon (BC) is an important component of PM2.5, which has recently received lots of attention due to its role in climate, health and air quality. It is generated by the incomplete combustion of carbonaceous fuels. In Megacities such as Beijing and Delhi, quantifying sources and emissions of BC is important as they are uncertain and changing due to rapid growth and urbanization. Therefore, identifying and quantifying these emission sources is critical for effective policy making and achieving the desired reduction in air pollution. This thesis presents measurements of BC fluxes using the Eddy covariance (EC) method. These measurements were made as part of the Air Pollution and human Health (APHH) research program. Firstly, measurements were made in Beijing, during the winter of 2016 (November- December) and summer of 2017 (May-June). Secondly, measurements were made in Delhi during pre-monsoon (May) and post-monsoon (October-November) seasons of 2018. In both experiments the focus was on characterising BC properties, particularly its mixing state, through analysis of the size and coating content of individual particles. The Single Particle Soot Photometer (SP2) was used to uniquely quantify the morphology-independent mass of single refractory BC particles and their coating content. As these properties of BC particles can be closely related to their emission sources, BC fluxes were also calculated according to their coating content to understand their local sources. In Beijing, for both seasons, the mean measured BC mass (winter: 5.49 ng m−2 s−1, summer: 6.10 ng m−2 s−1) and number fluxes (winter: 261.25 particles cm−2 s−1, summer: 334.37 particles cm−2 s−1) were similar. The coating characterised fluxes showed sources of > 90% of total flux measurements were from small lightly coated particles, which were related to traffic emissions. The flux measurements were also compared against co-emitted fluxes of NOx and CO, as well as emission inventories. In Delhi, both BC mass fluxes (25.8 ng m−2 s−1) and number fluxes (850 particles cm−2 s−1) were higher compared to Beijing. The fluxes calculated accordingly coating content showed, wide range of particles were emitted locally in Delhi, instead of one particular mode of BC. The source apportionments of BC particles in Delhi were performed with comparisons with Aerosol Mass Spectrometer (AMS) measurements and showed traffic and cooking were the dominant sources. In both cities, BC mass fluxes were an order of magnitude lower than the emission inventories.

Date of Award	5 May 2021
Original language	English
Awarding Institution	The University of Manchester
Supervisor	James Allan (Main Supervisor) & Hugh Coe (Co Supervisor)