1. Reductions in NO 2 Driven by Policy and Recession Patricia Castellanos 1 & K. Folkert Boersma 1,2 AGU 1 Royal Netherlands Meteorological Institute (KNMI) 2 Eindhoven University of Technology, Fluid Dynamics Lab

2. Why do we care about NO 2 over Europe? 2008 NO 2 Annual Mean [μg/m 3 ] Ozone precursor Aerosol formation Eutrophication of soil and water Acid deposition Toxic at high concentrations Limits were supposed to be reached by 2010 Timeline will be extended by 5 years without penalty Poorly quantified high biases Lack spatial representativity Reporting issues Need an independent assessment of changing NO 2 concentrations Bad air quality costs the UK 8.5-20 billion pounds per year, and can cut life expectancy by years – UK Environmental Audit Committee Satellite Observations

3. NO 2 Trends From Space Satellites provide –Global coverage –Independent & self-consistent time series Monitor effectiveness of pollution abatement strategies Trend [% per year]Time Period Richter et al. [2005]-3% to -4%1996-2004 van der A et al. [2008]-2% to -5% (mostly insignificant) 1996-2006 Konovalov et al. [2008]-2% to -5%1996-2005 Space-based European NO 2 column trends in the literature A Few % Per Year

4. NO 2 Column Trends Amsterdam Different summer and winter NO 2 lifetimes Large seasonal fluctuations –Normally only look at one season Transport effects in winter but not in summer –Cannot always assume some regular seasonal variability Separate the slow-moving trend from other variability

5. Frequency Separation – KZ Filter # of Iterations Transfer Function Trends based on low-pass filtered data K-iterations of a moving average

6. NO 2 Column Trends: August 2008/2005 2009/20052010/2005 2005 2006/2005 2007/2005

7. NO 2 Trends Relate to Economic Indicators

8. Fitting the NO 2 Trend Differentiate between policy (pre-recession) and recession related NO 2 changes European Average continuous continuous + recession

9. Recession Change European Average 2004-2010 Continuous Change [ C continuous x 6 years ][ C recession ]

10. One year of economic recession outweighed ~4-years of policy improvements Recession period reductions were the same or greater than pre-recession reductions

11. 2004-2007 Reported NO x Emissions trend ÷ C continuous trend UK reports reduced emissions but NO 2 has increased Report increased emissions but NO 2 has decreased Uncontrolled shipping emissions may be reducing air quality in the countries bordering the English channel

12. Final Remarks High resolution daily OMI observations allow us to analyze spatially AND temporally heterogeneous trends NO 2 concentrations over Europe are 10-50% lower than in 2004 Fast declines in NO x emissions during the economic recession led to 15-30% NO 2 reductions in 2008-09 Trend [% per year]Time Period Richter et al. [2005]-3% to -4%1996-2004 van der A et al. [2008]-2% to -5% (mostly insignificant) 1996-2006 Konovalov et al. [2008]-2% to -5%1996-2005 Castellanos & Boersma [2011]-2% to -5% -15 to -30% 2004-2008 2008-2009 European NO 2 column trends in the literature