Refractory black carbon emissions in Old Delhi quantified using the eddy covariance method

Our abilities to predict the extent and impacts of atmospheric black carbon depend on the accuracy of inventories, which are known to be highly uncertain in the developing world. This is because of less regulation of industry and vehicles, the private use of lower-quality fuels and appliances and a lack of data on activity. In order to provide better constraint on emissions from a developing megacity, the fluxes of refractory black carbon were measured using a Single Particle Soot Photometer (SP2) and the eddy covariance method, which is a relatively new technique. These were made on top of a purpose-built tower alongside a suite of other aerosol and gas flux measurements as part of the NERC/Newton Fund 'DelhiFlux' project, part of the Air Pollution and Human Health (APHH) Delhi programme. The location was the campus of the Indira Gandhi Delhi Technical University for Women (IGDTUW) in Old Delhi, where emissions were deemed to be representative of the less economically developed areas of the city.
Statistically significant rBC mass fluxes of around 10-30 ng m^-2 s^-1 were measured and these were strongest in the morning. The rBC particles observed could be categorised into distinct types according to their coating thicknesses according to the SP2 Leading Edge Only (LEO) method, however unlike previously published observations in London and Beijing, no clear sources could be attributed to the different coating types. Through comparisons with other measurements such as NO_x and AMS factorisation, it appears that the main sector responsible for rBC emissions in the area is transport, which is consistent with the SAFAR inventory, although cooking also seemed to contribute. However, the magnitude and diurnal profile of the measured emissions differed significantly from the inventory, with the measurements being lower by a factor of 50-60 and peaking earlier in the day.