Airborne Measurements of Nitryl Chloride and Implications for Chlorine Activation in the South Coast Air Basin of California J.M. Roberts; S.S. Brown; W.P. Dubé; J. Neuman; J.B. Nowak; C.A. Brock; A.M. Middlebrook; R. Bahreini; T.B. Ryerson; I.B. Pollack; P.R. Veres; A.K. Cochran; C. Warneke; J.A. de Gouw Photo: Sarah Lance Introduction to ClNO 2 chemistry: what do we know about it so far Measurements aboard the NOAA WP-3 During CalNex 2010 What does this tell us about ClNO 2 formation chemistry

Finlayson-Pitts, et al., 1989 N 2 O 5(g) + Cl - (aq) => ClNO 2(g) + NO 3 - (aq) ClNO 2 + h => Cl + NO 2 The Chemistry Requires N 2 O 5 (NO 2, O 3, Time,) Efficient N 2 O 5 uptake Aerosol Surface Area Aerosol Chloride Source of Soluble Chloride to Aerosol sea salt HCl H + + Cl - N 2 O 5 NO NO 2 + ClNO 2 HNO 3 NH 3 NH NH 3 NH NH 4 NO 3 NH 4 Cl

NOAA 43RF ClNO 2 Iodide ion CIMSJim Roberts, Andy Neuman, John Nowak NO 3, N 2 O 5 CaRDSSteve Brown, Bill Dube, Nick Wagner NO y, NO 2, NO, O 3 Chemiluminescence Tom Ryerson, Ilana Pollack NH 3 CIMS; John Nowak HNO 3 CIMS; Andy Neuman Aerosol Chemistry C-ToF AMS; Ann Middlebrook, Roya Bahreini Aerosol Surface Area NMASS/UHSASChuck Brock

NOAA P3 Flight patterns for May 24, 30, 31 and June 2, 3, 2010 Night Flights

Pasadena Site Mielke et al.,

N 2 O 5 almost absent Gradient within the RL dNO 3 /dt = k[NO 2 ][O 3 ] Residual of the Daytime Boundary Layer

N 2 O 5 almost absent Gradient within the RL dNO 3 /dt = k[NO 2 ][O 3 ] Residual of the Daytime Boundary Layer ClNO 2 + h => Cl + NO 2 Cl + RH => RO 2 RO 2 + NO => RO+NO 2 RO + O 2 => HO 2 + OVOC HO 2 + NO => NO 2 + OH Ozone Production

N 2 O 5, but not much ClNO 2 Low level leg over the Ocean

May 30, 2010 Flight –N 2 O 5 High, almost no ClNO 2 Mostly Org C Low RH Slow N 2 O 5 uptake San Bernadino Valley Ontario

High ClNO 2 close to ground

June 3, 2010 Flight – High ClNO 2 close to the ground Chino El Monte High RH, Efficient Uptake

Reaction efficiency vs. particle chloride N 2 O 5  NO NO 3 - NO Cl - => ClNO 2 NO H 2 O => HNO 3 + H + in the particle Bertram and Thornton, 2009 The chemistry is efficient even at modest [Cl-] Low [Cl - ] difficult to measure by AMS

Mass balance requires a gas phase source of soluble chloride HCl measurements at the Pasadena ground site J NO2 from the Lefer group If mid-day HCl is somewhat characteristic of the Daytime PBL then the Residual Layer has 2-6 ppbv HCl (see also Eldering, et al., Atmos. Environ., 25A, 2091, 1991) Trevor VandenBoer et al., P21 - Thursday

Box model of N 2 O 5 to ClNO 2 conversion R1 NO + O 3 => NO 2 + O 2 R2 NO 2 + O 3 => NO 3 R3 NO 3 + NO 2 N 2 O 5 R4 N 2 O 5 + Cl - (aerosol) => ClNO 2 + HNO 3 R5 N 2 O 5 + H 2 O (aerosol) => 2HNO 3 R6 NO 3 + NO => 2NO 2 } Sum: Total uptake rate Ratio: Reaction efficiency N 2 O 5 + H 2 O  NO 2 + (H 2 O) + NO 3 - Initialize with ambient measurements Adjust R4 and R5 to match N 2 O 5 and ClNO 2 at end time Calculate N 2 O 5 uptake and ClNO 2 formation efficiency Example Output

Ascent vs Descent  = 3.3 x % efficiency May 31, 2010 Flight

Some more results – maybe a summary May 30, 2010 Flight  = 4.4 x % efficiency 4:25 Hours since sunset 4:254:054:104:154:20 4:054:104:154:20

June 3, 2010 Flight  = 2.8 x % efficiency 8:50 Hours since sunset8:258:308:358:408:208:45 8:508:258:308:358:408:208:45

N 2 O 5 uptake coeff. What does this tell us about uptake coefficients. Figure 15. Chang et al., Aer. Sci. Technol., 45, , 2011.

Conclusions ClNO 2 is often abundant in the nighttime residual layer, measured mixing ratios were up to 3.7 ppbv. There is often enough aerosol surface area and chloride in the LA Basin to make the chemistry reasonably efficient. Low ClNO 2 production seems to be related to low N 2 O 5 uptake due to low RH and low aerosol chloride. Box model runs make much more HNO 3 /NO 3 - than is measured Further Work/Problems/Unknowns Nitrogen and Odd-Oxygen Balances O 3 production from Cl atom Chemistry Soluble Chloride Inventory