1. Nick Wagner, Steven S. Brown, William P. Dubé, Brian M. Lerner, Eric J. Williams - NOAA Earth System Research Lab, USA Theran Riedel, and Joel A. Thornton - University of Washington, USA Derek Coffman - Pacific Marine Environmental Laboratory, NOAA, Seattle, Washington, USA A. Vlasenko - Air Quality Research Division, Science and Technology Branch, Environment Canada, Canada Nocturnal Chemistry observed from the R/V Atlantis Observations of NO 3 and N 2 O 5 CalNEX Atlantis data meeting, January 11 th, 2011 1)Introduction to nocturnal nitrogen oxide chemistry and an overview of the nocturnal nitrogen measurements from the cruise. 2)Using a steady state analysis to determine NO 3 and N 2 O 5 loss rates. 3)Main losses for NO 3 and N 2 O 5 during CalNEX. 4)A discussion of meteorology night time outflow derived from P-3 flights. Outline

2. O3O3 NO 2 N2O5N2O5 ∆ H 2 O(l) NO 3 Cl - (aq) NO 2 HNO 3 Deposition ClNO 2 Nocturnal Chemical Mechanism O 3 and NO 2 react to produce NO 3. NO 3 is photoliable and exists in significant concentrations only at night. NO 3 and N 2 O 5 are usually in chemical equilibrium and rapidly inter convert. NO 3 is lost to reactions with VOCs. N 2 O 5 is lost to hydrolysis. Conventional view: In the aerosol N 2 O 5 is converted into NO 3 - and HNO3, which is lost to deposition. New mechanism: N 2 O 5 is convert to ClNO 2 in aerosol with Cl -. ClNO 2 builds throughout the night and is lost to photolysis in the morning.

3. Nighttime NO 3 Production NO 3 production rate: P(NO 3 ) = k [O 3 ] [NO 2 ]. Only nighttime data is shown. Polluted urban air masses. Shows where we expect to see nocturnal nitrogen oxide chemistry.

4. R/V Atlantis track - Colored by N 2 O 5 mixing ratio N 2 O 5 was mainly observed in Santa Monica and San Pedro Bay Many nights were spent stationary, and the measurements don’t show the spatial extent of the outflow. Only night time data is shown

5. Overview of Measured Mixing Ratios Observed mixing ratios of NO 3, N 2 O 5 and ClNO 2. Scale on each graph increases by x10. The marine boundary layer is chlorine-rich environment. A large fraction of the nocturnal nitrogen ends up as ClNO 2.

6. Lifetimes and Steady-State Analysis Gray bar shows time period of linear fit. Lifetimes are short < 15 min. In steady-state lifetimes can be related to pseudo first order loss coefficients. k N2O5 = 0.00072 +/- 0.00005 s -1 k NO3 = 0.0071 +/- 0.0005 s -1 Select periods time such that the loss rate coefficients are constant over the time period and produce a linear graph. R 2 = 0.90

7. Range of wind directions over the night Wind speeds 3-5 m/s. 1 hour is need to reach equilibrium. Based on lifetimes of ~15 min. 11 km to 18 km without fresh emissions is needed. Is the Steady-State Approximation Valid? Atlantis Location – anchored off Port of LA Future work include box model simulations to determine the time taken to reach steady state. Comparing ClNO 2 mixing ratio to the NO 3 production rate indicates at least 1 hour of processing. Argument 1Argument 2

8. Summary of Steady-State Fits Some uptake coefficients are not reasonable using measured surface area. RH was 90%-100%. Could hydroscopic growth or droplet formation result in unmeasured surface area? Osthoff, et al. JGR 2006. High N 2 O 5 losses due to fog. kN 2 O 5 (s -1 ) Measured Surface Area (  m 2 /cm 3 ) Uptake Coefficient (  ) Surface Area needed for  = 0.04 (%) 0.000722220.05 135% 0.000121820.01 22% 0.00121440.13 350% 0.00251300.32 800% 0.00211430.24 600% Unphysical

9. Large Surface Areas are Possible in Clouds Vertical profiles from the P-3 on June 2 nd and 3 rd, 2010. Through a marine stratus cloud. In the marine stratus cloud the surface area is >10 5  m 2 /cm 3. Large surface areas are associated with fast N 2 O 5 loss rates. From Sara Lance’s cloud probes.

10. NO 3 Loss Rate NO 3 losses to DMS are significant as expected in a marine environment. At times, DMS loss rate is comparable to the NO 3 production rate.

11. Conclusions A large fraction of nocturnal nitrogen ends up as ClNO 2. Both NO 3 reactions with VOCs (DMS) and N 2 O 5 hydrolysis are important losses. There is sometimes significant unmeasured surface area available for N 2 O 5 hydrolysis. Further Analysis: Apply this analysis to other nights. Confirm steady-state, using a box model with determined loss rates. See if the NO 3 loss rate can be attributed to VOCs measured by the GC and PTRTOF. Use box model calculations to determine N 2 O 5 loss rate and ClNO 2 yield and compare with the steady-state analysis.

12. Nighttime P-3 Flights over Water during CalNex 2010 Vertical Structure of Nighttime Outflow from L.A. Basin Outline: 1) Motivating Experiment – Shair, et al. (1982) 2) Case 1 Overview, Transport, Chemistry, Vertical profile 3) Case 2 Overview, Transport, Chemistry, Vertical profile

13. 1970’s transport study: SF 6 injected into power plant at El Segundo in early evening Motivation for CalNex Ship Based Nighttime Chemistry Study Measured plume overnight on a Navy vessel at various locations downwind Inferred transport in land breeze initiated aloft, eventually mixing to surface level Return transport during sea breeze the following day Can we confirm this transport pattern with Atlantis / P-3 measurements ? F. Shair, Atmos. Environ., 1982

14. 5/29 7 PM - 5/30 1 AM PDT5/30 10 PM - 5/31 4 AM PDT 6/02 1 - 7 AM PDT 6/03 1 - 8 AM PDT Four Los Angeles Night Flights in Five Days Local Sunset = 8:00 PM PDT Local Sunrise = 5:45 AM 13 nighttime or early morning aircraft “transects” over water 9 with clear tracers showing outflow, at least at some altitude range 4 with mainly inflow

15. May 30, 2010 Night Flight Day into night flight, several transects over water at varying altitude Clear outflow in region South of L.A., but inflow immediately West of L.A. Nearly as much NO 3 in outflow as in East Basin for this flight (but not others) Atlantis Overflight

16. Outflow associated with southeasterly wind, mainly in 200 – 400 m altitude range Wind direction at Atlantis SE, but point toward marine, rather than continental influence Atlantis Long Beach Flight Direction Long Beach May 30, Southerly Transect, Transport

17. CO levels most enhanced on return leg at 300 – 400 m Very little ClNO 2 anywhere on this flight, but some amount on lowest leg, possibly associated with a ship plume intercept Possibly some ClNO 2 near Atlantis intercept ? Atlantis Long Beach Flight Direction May 30, Southerly Transect, Chemistry

18. Potential T shows layers at 550, 350 and ~150 m, just at bottom of P-3 range Nearly 180 degrees wind shear from from 200 - 700 m – implications for depth of outflow Very dry above 400 m, likely very wet below 200: Large change in N 2 O 5 uptake / ClNO 2 production ? Vertical Profile, Long Beach, May 30 23:20 Local

19. June 3, 2010 Night Flight Night into day flight, transects over both water and desert (not shown) Outflow clearly persistent in regions to the West of L.A. on all over water transects But … as with other flights, pollution more concentration in east basin rather than in the outflow

20. Outflow in Santa Monica Bight associated with Northerly and Easterly wind Inflow aloft, above 1.5 km, with Northwesterly flow LAX Flight Direction June 3, West Transect, Transport LAX

21. Large ClNO 2 / N 2 O 5 in air transported directly from the East at 500 m as aircraft transects in toward Long Beach Horizontal extent ? Subsidence at sea ? Variability in vertical profile at LAX LAX Flight Direction June 3, West Transect, Chemistry LAX

22. Vertical Profile, LAX, June 3, 02:30 Local Layer structure at 250 m, stable above that level Wind shear: SW inflow below 250 m over LAX, NE outflow in layers aloft Stunning anticorrelation between ClNO 2 and N 2 O 5 in the vertical

23. Conclusions Daytime transport in L.A. Basin tends to concentration pollutants in East Basin; the most active nighttime chemistry (i.e., highest N 2 O 5, ClNO 2 ) observed there Nighttime transport, including outflow over water, was a persistent feature of several P-3 flights, but was not observed on every over water transect. Examples include: Southeasterly flow at surface level along coast Easterly flow at 500 m near Long Beach Northerly flow (down-slope?) in regions near Santa Monica bight Vertical profiles show complex structure in both chemistry and transport Future work: Comparison between Atlantis and P-3 measurements for over flight data Comparison of P-3 measurements of outflow characteristics to models

24. Limits on N 2 O 5 loss rate for May 20 th, 2010 Disagreement between production and loss rate due to: Similar disagreement for all nights during the cruise. 1)NO 3 and N 2 O 5 are not at steady-state. 2)There is a large surface area from particles with diameters >10  m. 3)A NO 3 loss. N 2 O 5 loss rate for a range of uptake coefficients. Uses measured surface area for particles < 10  m diameter.