1. Chemical transformations of pollutants during winter: First results from the WINTER 2015 aircraft campaign Lyatt Jaeglé, Viral Shah, Jessica Haskins, Joel Thornton, Felipe Lopez-Hilfiker, Ben Lee University of Washington, Department of Atmospheric Sciences Steve Brown (NOAA), Jose Jimenez (U Colorado), Jack Dibb (U New Hampshire), Ron Cohen (UC Berkeley), Rodney Weber (Georgia Tech), Andy Weinheimer, Teresa Campos, Eric Apel, Sam Hall (NCAR), Glenn Wolfe (NASA GSFC) What: Atmospheric chemistry aircraft campaign How: NSF/NCAR C-130 aircraft When: Feb 1-Mar 15 2015 Where: NE US (based at NASA Langley)

2.  Examine wintertime emissions (dormant biosphere!) and export  Characterize chemical transformations in winter when photochemistry is slow: nocturnal, multiphase processes  Understand factors controlling secondary aerosol formation Why WINTER? Fraction of NOx removal by N 2 O 5 Summer Winter 50-70% 30% NSF/NCAR C-130 aircraft flight tracks day SZA Feb-Mar 2015: 13 flights

3. DC-Philly-NYC pollution: Feb 3, 2015 NOx: Brown (NOAA); HNO 3 : Thornton (UW) pNO 3 : Jimenez (CU) New York City NOx: 970 hPa ppbv D.C. Philadelphia Obs:2.9 ppbv Model: 2.2 ppbv  Good agreement for NOx  Model pNO 3 too high by x2  overestimate in HNO 3 production? [Zhang et al., 2012; Heald et al, 2012] HNO 3 (g)+pNO 3 model obs UTC time D.C. Philly NYC [ model obs NO x

4. Infer γ (N 2 O 5 ) from observations (NO 3 ) -1, s -1 k[NO 2 ][O 3 ]/[NO 3 ] K eq [NO 2 ] ･ SA ･ c/4 slope Approach of Brown et al. (2006) Model: γ(N 2 O 5 )=0.02 Obs:γ(N 2 O 5 )=0.01 (0.02-0.004)  Modelγ(N 2 O 5 ) too high by a factor of 2- 4! NO 2, NO 3, N 2 O 5 : Brown (NOAA); N 2 O 5 (Lopez-Hilfiker) Nighttime NOx chemistry: Feb 3, 2015 Nighttime chemistry: NO 2 + O 3  NO 3 NO 3 + NO 2 ⇄ N 2 O 5 N 2 O 5 + aerosol  2HNO 3 γ(N 2 O 5 ) = f(RH, aerosol type, T) Mcintyre & Evans (2010), Zhang et al. (2012) model N2O5N2O5 NO 3 NO 2 Obs

5. Nighttime NOx chemistry: Feb 3, 2015 Nighttime production of ClNO 2 : N 2 O 5 + Cl -  ClNO 2 + NO 3 - In GEOS-Chem: Use γ’(N 2 O 5 ) =0.03 on sea salt and γ’(N 2 O 5 ) =0.006 for other aerosols ClNO 2 + h ν  NO 2 + Cl ClNO 2 Obs  Efficient production of ClNO 2 offshore! UTC time WINTER ClNO 2 observations MCM box model ClNO 2 : Lopez-Hilfiker & Thornton (UW) pptv ClNO 2 +hv O( 1 D)+H 2 O model

6. Vertical profiles: 9 WINTER flights O 3 : Campos (NCAR), NOx & NOy: Brown (NOAA), Aerosol: Jimenez (CU)  Model NO x too low by 50%  lower γ(N 2 O 5 )  longer lifetime?  emissions?  planetary boundary layer too shallow?  Model OK for O 3, but a bit low: low NOx?  Modeled pNO 3 too high by x2 Organic Nitrate Ammonium Sulfate Obs Model NOx obs model O3O3 pNO 3 too high

7. 2015 was a COLD winter in the NE US… Feb-Mar mean temperatures over NE US Temperature (°C) NOAA NCDC1901-2000 Mean: -2.7 o C 2012 2015 …how was nitrate affected? pNO 3 - /[pNO 3 - +HNO 3(g) ] Feb-Mar 2012 Feb-Mar 2015 pNO 3 fraction, % 2015: 70-90% as pNO 3 - 2012: 30-60% as pNO 3 - 950 hPa pNO 3 fraction, % WINTER Observations<1km

8. Next steps/questions  Why is N 2 O 5 aerosol uptake so slow?  What is the yield of ClNO 2 ? How does it affect the NOx lifetime, O 3 and VOCs?  Can use the WINTER observations to constrain emissions of pollutants and their export?  How to the aircraft observations relate to surface observations? A hazy sunrise over the Appalachians

9. PBL Height during winter: comparison to CALIPSO Planetary boundary layer heights derived from CALIPSO aerosol backscatter profiles February-March 2006-2012 PBLH CALIPSO 2006-2013 GEOS-FP 2013-2014 Ratio: CALIPSO/GEOS-FP Over land: GEOS-FP PBLH too low by 30%