Quantifying black carbon emissions from traffic and construction in central London using eddy covariance

Black carbon (BC) is a significant environmental health and climate forcing concern. Direct measurement of BC fluxes using eddy covariance can quantify emissions and identify sources. Previous studies have examined urban BC emissions in highly polluted countries such as China and India, but to date no equivalent research has been done in the UK and Europe. Here, we present black carbon flux data from a single particle soot photometer (SP2) deployed in an eddy covariance system at the BT (formerly British Telecommunications) Tower in central London. Mean BC mass (number) fluxes with a size range of 60 nm to 600 nm were 6.83 ng m−2 s−1 (443 cm−2 s−1) in summer and 13.3 ng m−2 s−1 (687 cm−2 s−1) in winter, indicating relatively low BC emission when compared to Delhi, which is likely due to the introduction of the ultra-low emission zone (ULEZ) and requirements for road diesel vehicles to meet Euro 6 standards or higher. However, flux footprint analysis identified strong point sources near construction sites during winter and summer observations, which implies that non-road mobile machinery (NRMM) emissions can dominate over traffic BC emissions. This implies that tightened NRMM regulations can help future air quality in London. Observations indicate that the UK's National Atmospheric Emissions Inventory (NAEI) overestimates BC emissions by a factor of 5, although large uncertainties are expected for the combustion sector in the manufacturing industry. The estimate of traffic emissions is more accurate.