Nocturnal Chemistry observed from the RV Atlantis Observations

Nocturnal Chemistry observed from the R/V Atlantis Observations of NO 3 and N 2 O 5 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 Outline 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 Cal. NEX. 4) A discussion of meteorology night time outflow derived from P-3 flights. Cal. NEX Atlantis data meeting, January 11 th, 2011

Nocturnal Chemical Mechanism • O 3 and NO 2 react to produce 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 2 O 3 NO 2 • 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 HNO 3, which is lost to deposition. • New mechanism: N 2 O 5 is convert to Cl. NO 2 in aerosol with Cl-. Cl. NO 2 builds throughout the night and is lost to photolysis in the morning. ∆ N 2 O 5 Cl- (aq) Cl. NO 2 H 2 O(l) HNO 3 Deposition

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.

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

Overview of Measured Mixing Ratios • Observed mixing ratios of NO 3, N 2 O 5 and Cl. NO 2. • Scale on each graph increases by x 10. • The marine boundary layer is chlorine-rich environment. • A large fraction of the nocturnal nitrogen ends up as Cl. NO 2.

Lifetimes and Steady-State Analysis • Lifetimes are short < 15 min. Gray bar shows time period of linear fit. • In steady-state lifetimes can be related to pseudo first order loss coefficients. • k. N 2 O 5 = 0. 00072 +/- 0. 00005 s-1 • k. NO 3 = 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

Is the Steady-State Approximation Valid? Argument 1 • Comparing Cl. NO 2 mixing ratio to the NO 3 production rate indicates at least 1 hour of processing. Argument 2 Atlantis Location – anchored off Port of LA 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. • Future work include box model simulations to determine the time taken to reach steady state.

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. k. N 2 O 5 (s-1) Measured Surface Area (mm 2/cm 3) Uptake Coefficient (g) Surface Area needed for g = 0. 04 (%) 0. 00072 222 0. 05 135% 0. 00012 182 0. 01 22% 0. 0012 144 0. 13 350% 0. 0025 130 0. 32 800% 0. 0021 143 0. 24 600% Unphysical

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 >105 mm 2/cm 3. • Large surface areas are associated with fast N 2 O 5 loss rates. • From Sara Lance’s cloud probes.

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.

Conclusions 1. A large fraction of nocturnal nitrogen ends up as Cl. NO 2. 2. Both NO 3 reactions with VOCs (DMS) and N 2 O 5 hydrolysis are important losses. 3. There is sometimes significant unmeasured surface area available for N 2 O 5 hydrolysis. Further Analysis: 1. Apply this analysis to other nights. 2. Confirm steady-state, using a box model with determined loss rates. 3. See if the NO 3 loss rate can be attributed to VOCs measured by the GC and PTRTOF. 4. Use box model calculations to determine N 2 O 5 loss rate and Cl. NO 2 yield and compare with the steady-state analysis.

Nighttime P-3 Flights over Water during Cal. Nex 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

Motivation for Cal. Nex Ship Based Nighttime Chemistry Study 1970’s transport study: SF 6 injected into power plant at El Segundo in early evening • 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

Four Los Angeles Night Flights in Five Days 5/29 7 PM - 5/30 1 AM PDT 5/30 10 PM - 5/31 4 AM PDT Local Sunset = 8: 00 PM PDT 6/02 1 - 7 AM PDT 6/03 1 - 8 AM 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

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

May 30, Southerly Transect, Transport Atlantis Long Beach Flight Direction 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

May 30, Southerly Transect, Chemistry Atlantis Long Beach Flight Direction • CO levels most enhanced on return leg at 300 – 400 m • Very little Cl. NO 2 anywhere on this flight, but some amount on lowest leg, possibly associated with a ship plume intercept • Possibly some Cl. NO 2 near Atlantis intercept ?

Vertical Profile, Long Beach, May 30 23: 20 Local • Potential T shows layers at 550, 350 and ~150 m, just at bottom of P-3 range • Nearly 180 degrees wind shear 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 / Cl. NO 2 production ?

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

June 3, West Transect, Transport LAX Flight Direction • Outflow in Santa Monica Bight associated with Northerly and Easterly wind • Inflow aloft, above 1. 5 km, with Northwesterly flow

June 3, West Transect, Chemistry LAX Flight Direction • Large Cl. NO 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

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 Cl. NO 2 and N 2 O 5 in the vertical

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, Cl. NO 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

Limits on N 2 O 5 loss rate for May 20 th, 2010 • N 2 O 5 loss rate for a range of uptake coefficients. • Uses measured surface area for particles < 10 mm diameter. • Disagreement between production and loss rate due to: 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 mm. 3) A NO 3 loss. • Similar disagreement for all nights during the cruise.