Measurement of NOx Fluxes from a Tall Tower in Central London, UK and Comparison with Emissions Inventories

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• 作者：James D. Lee ; Carole Helfter ; Ruth M. Purvis ; Sean D. Beevers ; David C. Carslaw ; Alastair C. Lewis ; Sarah J. M酶ller ; Anja Tremper ; Adam Vaughan ; Eiko G. Nemitz
• 刊名：Environmental Science & Technology
• 出版年：2015
• 出版时间：January 20, 2015
• 年：2015
• 卷：49
• 期：2
• 页码：1025-1034
• 全文大小：497K
• ISSN：1520-5851

文摘

Direct measurements of NO_x concentration and flux were made from a tall tower in central London, UK as part of the Clean Air for London (ClearfLo) project. Fast time resolution (10 Hz) NO and NO₂ concentrations were measured and combined with fast vertical wind measurements to provide top-down flux estimates using the eddy covariance technique. Measured NO_x fluxes were usually positive and ranged from close to zero at night to 2000鈥?000 ng m^鈥? s^鈥? during the day. Peak fluxes were usually observed in the morning, coincident with the maximum traffic flow. Measurements of the NO_x flux have been scaled and compared to the UK National Atmospheric Emissions Inventory (NAEI) estimate of NO_x emission for the measurement footprint. The measurements are on average 80% higher than the NAEI emission inventory for all of London. Observations made in westerly airflow (from parts of London where traffic is a smaller fraction of the NO_x source) showed a better agreement on average with the inventory. The observations suggest that the emissions inventory is poorest at estimating NO_x when traffic is the dominant source, in this case from an easterly direction from the BT Tower. Agreement between the measurements and the London Atmospheric Emissions Inventory (LAEI) are better, due to the more explicit treatment of traffic flow by this more detailed inventory. The flux observations support previous tailpipe observations of higher NO_x emitted from the London vehicle diesel fleet than is represented in the NAEI or predicted for several EURO emission control technologies. Higher-than-anticipated vehicle NO_x is likely responsible for the significant discrepancies that exist in London between observed NO_x and long-term NO_x projections.