Spatial and temporal dynamics of atmospheric pollutants in
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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.
Long-term Measurements in London Anemometer & sampling inlet 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 - NOx and O 3 fluxes • 2014 – N 2 O fluxes (Campaign) • 2015 – N 2 O fluxes Instrument location Sampling height 190 m above street level
The BT Tower – Flux Footprint 90 th percentile 10 th percentile 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
Flux Inventory Measurements Top-down Validation of Emission Inventories: GHGs Annual budgets: Excellent agreement between measurements and inventory (CO and CO 2) Large spatial variability and seasonality observed for all 3 gases but discrepancy between measured and inventory CH 4 budget. What CH 4 source(s) is the inventory missing/ underestimating? Perhaps biogenic?
Top-down Validation of Emission Inventories: NOx West Footprint • Urban parkland • Lower traffic density • Traffic < NOx source East Footprint • Fewer green areas • Higher traffic density • Traffic > NOx source Lee, J. D. et al. : Environ. Sci. Technol. 49, 1025 -1034, 2015.
Top-down Validation of Emission Inventories: VOCs Temporal Trends Acetaldehyde Isoprene Comparison with NAEI Benzene Flux Measurements Fluxes and concentrations highest in August and September (coupled to light and air temperature). VOC [t km-2 yr-1] National Atmospheric Emission Inventory (NAEI) Fluxes: low seasonality (50% -90% emissions attributed to traffic). Boundary layer height or advection explains winter increase in concentrations. Langford, B. et al. : Atmos. Chem. Phys. , 10, 627 -645, 2010. Valach, A. et al. : Atmos. Chem. Phys. , 15, 7777– 7796, 2015.
