TITLE: INDOEX: Ship Ron Brown Chemistry Nitrogen Oxides (Carsey) AUTHOR: Thomas P. Carsey NOAA Atlantic Oceanographic and Meteorological Lab. Ocean Chemistry Division 4301 Rickenbacker Causeway Miami, Florida 33149 email carsey@aoml.noaa.gov phone (305) 361-4386 fax (305) 361-4392 1.0 DATA SET OVERVIEW This data set contains measurements of nitrogen oxides made on the Ron Brown ship during the INDOEX project. 2.0 INSTRUMENT DESCRIPTION Nitrogen oxides were measured by a chemiluminescence instrument built according to established protocols [e.g., Ridley et al. 1988; Carroll et al. 1985]. Air inlets for NO and NO2, along with the NO2 permeation device, and various valves were housed in a sampling box suspended on a forward support beam of the atmospheric sampling tower on the NOAA ship RONALD H. BROWN (see Figure 1). About 20 m of 3"-OD Teflon sampling lines ran from the box to the van. This sampling box was plumbed to allow NO and NO2 calibration gases to be inserted into the sampling line inside the sample box. To avoid contamination by sea salt aerosols, the NO/NO2 inlet was capped by a 37-mm diameter 1-m pore size Teflon filter (Gelman), replaced frequently during the cruise. Figure 1 (http://www.joss.ucar.edu/data/indoex/docs/aoml_fig1.gif) Figure 2 (http://www.joss.ucar.edu/data/indoex/docs/aoml_fig2.gif) NO2 analysis Sampled air was routed from the box to the van through one sample line. For flow through the lines was regulated by a mass-flow controller set at 1.2 L/m inside the sampling box. A needle valve in the air line at the instrument rack further reduced the pressure and decreased gas travel time from the sampling box to the equipment rack to less than five seconds. Conversion of NO2 into NO for chemiluminescence detection was accomplished within a 0.8-L photolysis chamber illuminated by a 300 watt Xenon lamp (ILC Technology). The sampled air flowed through the photolysis chamber at all times; for all measurements other than the NO2 ambient and NO2 calibrate, a motor- driven shutter system was employed to block the light path. Overall efficiency of the cell was monitored throughout the cruise, see table below. The photolysis lamp power supply failed repeatedly during the cruise; in addition, a possible contamination of the NO2 signal from the photolysis chamber may have effected the data and is currently being investigated. For NOy analysis, air was passed through a quartz glass tube containing molybdenum wire or gauze at ~350NC to generate NO gas. Several converter tubes were employed. Efficiencies of NO2 conversion were measured throughout the cruise, see below. The NO was measured by mixing with ozone within a gold coated stainless steel reaction chamber and measuring the resulting chemiluminescent emission. The emitted photons were recorded by a 9658R photomultiplier tube (Thorn EMI) held at 1250 volts and housed in a cooled housing (Products For Research) maintained nominally at -40NC; this cooler failed and was replaced by a similar system during Leg 2. A timing sequence was established for the sequential determinations of NO NO2 and NOy, with a cycle time (including data recording and setup restarting) of about twenty minutes. Calibrations for all three analytes were performed frequently, usually daily. Photon counting intervals of 10 seconds were recorded for the duration of the cycle. The first 2-3 minutes of each measure and calibrate count segments were ignored to allow the system to equilibrate. Each run was scanned for spikes or other anomalies due to other shipboard instrumentation; questionable 10-second counts were deleted. For each rate, the resulting 10-second count values were averaged and converted to counts per second. Blank (zero) values were determined by reacting the gas stream with excess ozone prior to entering the reaction chamber. The sensitivities (counts per second per parts per trillion, cps/ppt) of the instrument were determined by standard techniques. For NO, a commercial calibration gas mixture (4.94 ppbv NO in N2, Scott Specialty Gas) was injected into the inlet stream. For NO2, an 80 cc/min N2 gas stream which passed over an NO2 permeation device (VICI Metronics) housed in an insulated chamber held at 30NC (Thermologic) and added to the ambient air stream. The permeation rate of the device was determined from gravimetric analysis to be -44.14 ng/min. Concentrations are noted as averages of seven sequential measurements for NO2 and NOy; thirteen measurements for NO. Instrument characteristics averaged over cruise legs are given below. Leg 1 Leg 2 Leg 3 NO sens 4.2 3.6 3.0 NO LLD 6.4 8.6 5.4 NO2 sens - 1.0 1.5 NO2 LLD - 37.2 10.5 NO2 Eff% - 28.1 49.2 NOY sens 1.4 1.7 1.5 NOY LLD 19.1 18.2 11.0 NOY Eff% 33.7 48.5 51.5 sens = cps/ppt; LLD = lower limit of detection, =2p2/S*r(Rb/Rt), where S=sens, Rb = background count rate and Rt is the background counting time; Eff from ratio of sensitivities.