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