1. Department of Atmospheric Sciences, University of Washington
Wintertime emissions and chemistry over the N.E. US: Role of oxidants and heterogeneous chemistry
Lyatt Jaeglé, Viral Shah, Joel Thornton, Felipe Lopez-Hilfiker, Ben Lee
Department of Atmospheric Sciences, University of Washington
S. Brown (NOAA), J. Jimenez (U Colorado), J. Dibb (U New Hampshire), R. Cohen (UC Berkeley), R. Weber (Georgia Tech), A. Weinheimer, T. Campos, E. Apel (NCAR), G. Wolfe (UMBC), J. DiGangi (NASA Langley), T. Hanisco (NASA GSFC)
How well do we understand wintertime emissions of pollutants?
How important are nocturnal & multiphase processes?
What factors control aerosol formation and aerosol/gas partitioning?
 Viral Shah (talk); Jessica Haskins, Kelsey Larson (posters) on Tuesday

2. NSF/NCAR C-130 aircraft flight tracks
WINTER: Feb 3 - Mar
NSF/NCAR C-130 aircraft flight tracks
Measurements
Gas-phase: NO2, NO, HNO3, N2O5, ∑PANs, ∑ANs, HONO, NOy, ClNO2, HCl, Cl2, CO, O3, SO2, NH3, CH2O, alkanes, alkenes, alkynes, CFCs, halons
Aerosol composition (ToF-AMS, PILS, Filter): organic aerosol, SO42-, NH3+, NO3-, Cl-, Na+, Mg2+, Ca2+
Aerosol size distribution, actinic flux, meteorological parameters
50% of flight hours at night
71% within 1 km of the surface (3,000 feet)
13 flights
SZA
GEOS-Chem Model
Nested grid (0.5ºx0.625º). v10-01
Scale EPA NEI 2011 to 2015:
20% reduction in NOx (2015 CEMS + 7%/yr decrease in transportation)
32% reduction in SO2 (2015 CEMS)
day
50% of flights hours at night
71% within 1 km of the surface

3. Vertical profiles over land
Anthropogenic emissions
NOx
HCHO 50 40 30 20 10 5 4 3 2 1
NOx emissions
58% transportation
29% stationary FF
13% industry
HCHO emissions
60% transportation
28% stationary FF
12% industry
change (%)
∆HO2
Impact on oxidants
5xHCHO + ClNO2 chemistry
40-80% increase in HOx
10-20% increase in SO4= & OA
1010 atoms cm-2 s-1
Vertical profiles over land
NOy
HCHO
observations
model
model 5xNEI
observations
model
NOy within 10% of observations, but HCHO too low by x2
Increase NEI HCHO emissions by x5 (cold-start OVOC emissions?)

4. NOy partitioning during WINTER
NOy partitioning (<1km)
Nighttime NOz (NOy-NOx)
PNs
ANs
N2O5
HNO3
ClNO2
HONO
Obs
Model
means for
all flights
HNO3
N2O5
ANs
PNs
NOx
Obs
Model
ANs = RONO2 PNs = RO2NO2
Model HNO3 too high x4
[Zhang et al., 2012; Heald et al, 2012]
Model N2O5 too low by x4
 Problem with ɣ(N2O5)?
GEOS-Chem [Evans & Jacob, 2005]:
ɣ(N2O5) = f(RH, aerosol, T)~0.02

5. Update ɣ(N2O5) to more recent lab obs
ɣ(N2O5) – inhibited by nitrate and organics
SO4=-NO3--NH4+ aerosol ɣ = f(H2O, NO3-, Cl-) [Bertram & Thornton, 2009]
Organic aerosol ɣ = (RH<50%), (RH>50%) [Badger et al., 2006]
ClNO2 yield, 𝝓
SO4=-NO3--NH4+ aerosol 𝝓 = f(H2O, Cl-) [Bertram & Thornton, 2009]
Sea salt 𝝓=1, other aerosol 𝝓=0
New ɣ(N2O5)
New 𝝓(ClNO2)
ɣ(N2O5)<0.01
𝝓 <0.2
ɣ(N2O5)>0.02
𝝓 =1
Feb-Mar surface

6. Improved NOy partitioning
HNO3 + pNO3
Nighttime NOz (NOy-NOx) (<1 km)
observations
model
model, new ɣN2O5
HNO3
model, new ɣN2O5+𝑣d
HONO
ClNO2
N2O5
ANs
PNs
Obs
Model
Updated model
(new ɣN2O5+𝑣d) O3
observations
model
model, new 𝑣d
New ɣ(N2O5) + Update dry deposition
Surface resistance (Rc) ↑ at cold temp ~ exp(-T-4) [Wesely, 1989]
Set Rc(HNO3)=0 [Wesely and Hicks, 2000]  𝑣d(HNO3)~1-4 cm s-1
Other species: limit Rc increase by x2  𝑣d(O3) increases by 40%

7. Summary ClNO2 NOx HNO3 Org nit. 15% 75% 10%
Oxidative capacity of wintertime polluted air controlled by regional anthropogenic emissions and multiphase chemistry
Nitrate + OA suppression of ɣ(N2O5) + corrected dry dep  helps address long-standing winter HNO3/nitrate overestimate problem
GEOS-Chem budget (NE US 0-1km)
15%
ClNO2
ClNO2
Org nit.
NO2+OH
44%
75%
NOx
HNO3
NOx
N2O5+aer
55%
NOx 𝜏
=1.2d
HNO3
NO3+VOC
10%
Org nit.