Remote sensing of NO2 emission from the central urban area of Shanghai (China) using the mobile DOAS technique

The mobile DOAS technique was used to quantify the NOx vehicle emission of the central urban area, enclosed by the Inner Ring Viaduct Road (IRVR), of Shanghai, China. Three field measurement campaigns were performed during the pre-EXPO period in October 2009, the EXPO opening ceremony, and the closing ceremony period in 2010. The spatial and temporal distributions of NO2 Vertical Column Densities were derived, and the effects of traffic and wind conditions were studied. The averaged NO2 emissions rates from the IRVR area were determined to be 2.1 +/- 0.9 ton/h, 2.8 +/- 1.4 ton/h and 2.7 +/- 1.4 ton/h for these three campaigns. The annual vehicle NOx emissions for the central urban area were estimated to be (2.3 +/- 1.0) x 10(4) ton in 2009 and (3.0 +/- 1.5) x 10(4) ton in 2010, and those for the whole city were (13.4 +/- 5.9) x 10(4) ton in 2009 and (17.6 +/- 8.4) x 10(4) ton in 2010, by considering a typical NO/NO2NO2 ratio, NOx lifetime, as well as the traffic emission share of central urban area with respect to the entire city. The vehicle NOx emissions quantified by mobile DOAS were found to exhibit an increasing trend in the central urban area of Shanghai, by 1.6 times and 2.1 times from 2006 to 2009 and 2010. Due to wind field variations, unknown NOx chemical transformation, and uncertainties in AMFs, the systematic derivation of the final NOx emission rates obtained was about 55% for averaged several consecutive days.