1. Spatial and temporal dynamics of atmospheric pollutants in London, UK. Carole Helfter, Eiko Nemitz, Chiara Di Marco, Ben Langford, Neil Mullinger, Ute Skiba To provide a top-down validation of bottom-up emission inventories (i) emissions of CO, CO 2 and aromatic VOCs are well captured by atmospheric inventories; (ii) NOx and CH 4 are underestimated.

2. Long-term Measurements in London Timeline of Measurements 2006 - CO 2 /CO/VOC Fluxes (campaign) 2007 - PM 1 Aerosol Fluxes (campaign) 2011 – Continuous EC fluxes of CO 2 /CO/CH 4 /H 2 O 2012-2013 - NO x and O 3 fluxes 2014 – N 2 O fluxes (Campaign) 2015 – N 2 O fluxes Anemometer & sampling inlet Instrument location Sampling height 190 m above street level

3. The BT Tower – Flux Footprint . Central London  Footprint 180 km 2.  Mean building height 12 m.  Typically 2-4 km from the tower (6 km to North).  N-NW: Mainly residential.  E & W: gradient commercial – residential.  SE – SW: heavily built-up, commercial.  Footprint entrains Thames river SE of tower 90 th percentile 10 th percentile Flux Footprint

4. Annual budgets: Top-down Validation of Emission Inventories: GHGs Excellent agreement between measurements and inventory (CO and CO 2 ) What CH 4 source(s) is the inventory missing/ underestimating? Perhaps biogenic? Flux Measurements Inventory Large spatial variability and seasonality observed for all 3 gases but discrepancy between measured and inventory CH 4 budget.

5. West Footprint Urban parkland Lower traffic density Traffic < NO x source East Footprint Fewer green areas Higher traffic density Traffic > NOx source Top-down Validation of Emission Inventories: NO x Lee, J. D. et al.: Environ. Sci. Technol. 49, 1025-1034, 2015.

6. Top-down Validation of Emission Inventories: VOCs Isoprene BenzeneAcetaldehyde Flux Measurements National Atmospheric Emission Inventory (NAEI) Langford, B. et al.: Atmos. Chem. Phys., 10, 627-645, 2010. Valach, A. et al.: Atmos. Chem. Phys., 15, 7777–7796, 2015. VOC [t km -2 yr -1 ] Comparison with NAEI Temporal Trends Fluxes: low seasonality (50%-90% emissions attributed to traffic). Boundary layer height or advection explains winter increase in concentrations. Fluxes and concentrations highest in August and September (coupled to light and air temperature).