Atmospheric Chemistry Speciation Studies Using the Jetstream Aircraft - Summary Report This report describes the work actually carried out by ACRU using the Cranfield Jetstream aircraft during the EASE96 and EASE97 ACSOE campaigns in western Ireland. Owing to the financial problems which the ACSOE community faced the final decision about what the Jetstream should do and how much money would be available to do it was made only very shortly before the work had to begin. In the event it was decided that the Jetstream should carry out experiments within both the MAGE and OXICOA components of the ACSOE campaign based at Mace Head in 1996. One of the main objectives for both was to put the atmospheric observations made at Mace Head (and on the ship Challenger during MAGE) into a three dimensional context by flying vertical profiles and horizontal traverses in the neighbourhoods of the surface stations. During MAGE the flights at Mace Head and the ship were to be made during periods of connected airflow between the ship and Mace Head and timed so the as far as possible the same air was sampled first over the upwind one of the pair of surface stations and then over the downwind one, that is, a Lagrangian pair of flights. Both physical (meteorological) and chemical (ozone and nitrogen oxides) species were to be measured and air and aerosol samples taken to enable analyses to be made of the production and transformation of marine sulphur species (DMS and MSA) and of some hydrocarbons. The aircraft flew on two days of the intended four during the 1996 MAGE campaign. Technical difficulties and the early departure of the ship prevented any more flights being made so the Jetstream returned to Galway in May 1997 and made two more pairs of flights (perhaps in more suitable weather). In 1996 the Jetstream made seven flights on five days during the OXICOA campaign. In the event it did fly in the two years the whole of its planned hours. The report summarises some of the principal observations with a few comments. The characteristics particularly reported are the vertical structures (winds, inversions and ozone and NO2 strata) and horizontal variability of some parameters. For the MAGE flights the mutual consistency of the upwind and downwind legs of the flights has been examined. This was service work for the Mace Head and ship investigators and not a research project in its own right. MAGE Flight Plans The 1996 flights were carried out in strong westerly winds and the upwind and downwind parts were flown without refuelling. On the 28th June the outward transit was made at low level and air samples were taken and filters were exposed at various distances downwind. On the 1st July the outward transit was made above the boundary layer and air samples and filters were taken at the ship and at Mace Head. The 1997 flights were made in winds slightly east of south and in each case a morning flight was made consisting of traverses within and above the boundary layer and a controlled ascent offshore Mace Head with a similar flight in the afternoon over the ship. The return to Galway was made via Mace Head. OXICOA Flight Plans Flight plans, consisting mainly of controlled ascents and descents, were agreed beforehand to be determined by the wind direction and back trajectory and synoptic situation prevailing on the flight day. The different synoptic patterns recognised and planned for were categorised as clean westerly, polluted westerly and easterly. Three flights were made on the 23rd July 1996, in early morning, at midday and in the afternoon in order to examine the constancy of the conditions during the daytime. One early morning high altitude flight was planned to follow a clear calm night during which the DOAS group at Mace Head had made nitrate radical observations and was intended to give the observers there an idea of the relevant concentration profiles (NO2 and ozone) in which the observations had been made. The flight consisted of a climb made before solar activity had become significant, to about 7800m (the aircraft's ceiling) at 300m/minute and a slower descent (150m/min) with stops to collect air samples for hydrocarbons. MAGE Flights Horizontal Variability and Vertical Structure and 'Connectedness' An attempt is made here to compare the upwind and downwind parts of the flights in order to allow their 'connectedness' to be judged, since the intention had been to sample the same air twice in what was forecast to be direct flows between Mace Head and the ship 'Challenger' about 100 miles offshore. Flights During EASE96 Winds were recorded in the co-pilot's log from the aircraft's Inertial Reference System readings, they are successive spot values given for selected traverses and the profile ascents. The best accuracy given for them is +-4.5ms-1 +-10o 28th June 1996 Winds Mace Head 152m 325o 7ms-1 325o 8ms-1 400m 318o 13ms-1 Air Sampling Holds 1/3 distance between Mace Head and ship 1233-1235 400m 325o 15ms-1 1240-1236 40m 315o 14ms-1 Air Sampling Holds 2/3 distance between Mace Head and ship 1255-1257 20m 310o 13ms-1 314o 17ms-1 1258-1304 400m 315o 14ms-1 Ship 40m 1333 285o 13ms-1 1st June 1996 Ship 40m 1041-1100 312o 14ms-1 Mace Head 45m 1138-1139 299o 11ms-1 Variability of logged Parameters During Traverses 28.6.96 Mace Head Mean SD* RSD%# Mean SD RSD% Altitude mASL 152 11.0 7.2 353 15.8 4.5 Air Temp Deg C 17.7 0.07 0.4 14.1 0.3 2.2 Ozone ppb 47.4 0.6 1.3 47.8 0.6 1.3 * standard deviation # standard deviation/mean% One Third Stop Altitude 20 5.3 26.5 374 2.4 0.6 Air Temp 17.7 0.07 7.2 15.6 0.6 3.8 Ozone 52.5 0.5 1.0 51.5 1.0 1.9 Two-Thirds Stop Altitude 40 6.9 17.3 362 7.8 2.2 Air Temp 18.0 0.06 0.3 14.6 0.05 0.3 Ozone 53.2 0.5 0.9 52.7 0.5 0.9 Ship Altitude 40 4.0 10.0 Air Temp 18.0 0.06 0.3 Ozone 45.8 0.4 0.9 1.7.96 Ship Low Altitude 40m Traverse Mace Head Mean SD RSD% Mean SD RSD% Altitude 40 10.9 - 44.5 14.5 0.3 Air Temp 17.1 1.2 7.2 16.9 0.1 0.3 Ozone 35.7 0.7 0.2 38.8 0.3 0.8 NO2 ppb 0.3 0.2 60.8 0.3 0.004 1.3 On both days the ozone was very uniform with a low relative standard deviation indicating well- mixed air. Where there were modest plumes (2-10ppb nothing more was seen) within relatively uniform traverses the instrumental noise contributes about equally to the plumes for the NOx instrument whereas for the Scintrex LMA3 NO2 (quoted in this report) and the ozone instruments, the plume structures dominate. Flights during EASE97 Winds were south of east and moderate on both flight days, 22nd and 23rd May. 22nd May Flight 60m upwind (Mace Head) run, 0937-0958 northward, successive wind readings 127o 4ms-1 085o 6ms-1 104o 5ms-1 070o 8ms-1 (over sea) 089o 8ms-1 120o 10ms-1 134o 9ms-1 over land north of Mace Head 60m downwind traverse (ship) 1325-1340 northward 094o 6ms-1 (S of track start) 116o 6ms-1 (ship) 119o 7ms-1 101o 6ms-1 300m upwind run 105430-110930 southward 095o 12ms-1 097o 7ms-1 086o 6ms-1 103o 13kt 083o 6ms-1 088o 6ms-1 700m downwind run 1437-145830 southward 120o 9ms-1 123o 7ms-1 123o 7ms-1 120o 7ms-1 112o 6ms-1 Profile winds Altitude Upwind Downwind ft m Deg/ms-1 Deg/ms-1 500 152 134/9 1000 305 104/8 105/9 2000 610 150/5 105/8 3000 915 160/2 120/7 4000 1220 132/5 113/6 5000 1500 134/6 137/3 6000 1830 134/6 144/6 7000 2150 cloud tops 161/6 7500 2300 155/9 8000 2450 150/8 9000 2750 167/6 23rd May Flight 60m run 0913-0937 GMT northward track, 090o 11ms-1 095o 11ms-1 090o 10ms-1 081o 10ms-1 (track over sea until north of Mace Head, then up a valley) 60m Downwind run (ship), 1328-1344 northward 104o 9ms-1 114o 5ms-1 118o 5ms-1 105o 8ms-1 300m upwind (Mace Head) run 103130-1050 southward 104o 9ms-1 114o 15ms-1 095o 14ms-1 089o 12ms-1 087o 12ms-1 300m downwind (ship) run 1439-1500 southward 115o 9ms-1 117o 12ms-1 118o 13ms-1 105o 12ms-1 Profile winds (Deg/ms-1) Altitude ft m Upwind Downwind 1000 300 115/7 1500 460 123/9 2000 610 116/12 123/9 3000 915 124/11 125/9 Downwind directions 4000 1220 134/9 136/6 notably veered on upwind 5000 1500 136/9 131/6 with lower speeds 6000 1830 121/11 134/7 Inversion at 2300m 7000 2150 119/8 116/7 8000 2450 129/8 107/6 9000 2750 110/7 106/6 10000 3050 122/7 105/2 Variability of Logged Parameters During Traverses 22nd May 300/700m Traverses am pm Mean SD RSD% Mean SD RSD% Altitude 330.2 71.2 24.6 755.4 6.8 9.0 Air T 10.0 0.7 6.6 8.7 0.5 5.9 Ozone 52.4 6.5 12.4 54.1 3.9 7.2 NOx 1.7 1.2 70.4 2.5 5.4 216.3 NO 0.5 0.6 122.4 0.8 2.3 282.0 NO2 1.2 0.8 68.0 4.8 8.7 182.7 No ozone increase downwind this day 23rd May 300m Traverses am pm Mean SD RSD% Mean SD RSD% Altitude 446.4 10.6 2.4 461.4 7.9 1.7 Air T 8.8 0.4 4.5 9.5 0.1 1.3 Ozone 35.6 3.7 10.3 50.3 1.7 3.4 NOx 3.8 1.4 36.8 2.1 1.0 45.9 NO 0.6 0.6 88.8 0. 0.5 - NO2 2.7 1.1 39.6 0.5 0.4 73.3 Downwind ozone increase perhaps indicates photochemistry this day The larger ozone RSD upwind indicates concentration structure in offshore winds. This variability is apparently reduced by travel over the sea to the ship. Summary of Ship-Mace Head Separations Compared with Observed Winds Ship positions from pilot's log or inferred from flight tracks. 28.6.96 Ship to Mace Head 299o 167km Separation time of low altitude traverses at ship and Mace head 48 min (both done in one flight). Required wind for Lagrangian connection 299o 58ms-1 Winds reported Ship 314o 12.5ms-1 Mace Head 325o 7ms-1 1.7.96 Ship to Mace Head 295o 130km Separation time of ship and Mace Head low altitude traverses (only one flight) 50min, wind speed required for Lagrangian connection 43ms-1 Winds reported Ship 312o 14ms-1 Mace Head 299o 11ms-1 The plans flown were those agreed with the MAGE campaign manager 22.5.97 Mace Head to Ship 88o 93km Separation of Mace Head and Ship low altitude traverses 4h. Required wind for Lagrangian connection 88o 6.4ms-1 Winds observed Mace Head 100o 6ms-1 Ship 116o 6ms-1 both with large variations Ship position may have been unsuitable for Lagrangian connection though wind speeds were suitable (or pilot's reported ship position may have been incorrect) 23.5 97 Mace Head to ship 106o 106km Separation of Mace head and Ship low altitude traverses 4.2h Required wind for Lagrangian connection 108o 6ms-1 Winds observed Mace Head 090o 20kt Ship 108o 6ms-1 This flight closest to Lagrangian. Profile Ascents - Other Characteristics 28th June 1996 Temperature Gradient 1st profile 71-1156m 8.8oC/km Inversion 3oC at 1200m O3 increases 45-50ppb up to 1200m then sharper increase 2nd profile, inversions 505 0.6o and 1200m 3.7o, gradients <321m 6.0oC/km, 353-505m 3.3oC/km, 538-1052m 5.3oC/km Ozone 53-55ppb surface to 1200m then peaks at 65ppb at inversion 1st July 1996 Descent at ship inversion 1500m 1.0o Temperature Gradients <1314m 7.5oC/km, 1675-2261m 4.1oC/km O3 33-40ppb below 1500m (inversion) then rise with layering above Ascent at Mace Head, showers, no inversion, temperature gradients 75-635m 7.5oC/km 879-1026m 11.6oC/km, 1026-2024m 4.2oC/km O3 38-42ppb surface to 2400m then rise to 48ppb and fall 22nd May 1997 am Temperature Gradients 631-1117m (inversions 1117 2000m 0.2o) 5.9oC/km 1223-2000m 6.6oC/km 2099-2371m 4.8oC/km Cloud 500-2000m, Relative Humidity falls rapidly above 2000m, O3 rises and NO2 falls sharply at 300m. O3 rises more rapidly above 2000m pm Temperature Gradients - only sign of inversion 533m, slight slackening of gradient 63-1570m 6.0oC/km 1591-2055m 8.5oC/km (anything above 7 may suggest instability) Relative Humidity declines 800-1600m then rises. Cloud 400m 'dark layer' 2000m. O3 rises 38-45ppb at 200m then constant, NO2 zero. 23rd May 1997 am Temperature Gradient Small inversions 222 669 1094 2191m 0.5o, overall gradients 66-2184m 5.3K/km Clouds 500 1500 2200m, Relative Humidity falls sharply at 700m. O3 rises and NO2 falls sharply at 700m, NO2 then zero. O3 rises steadily 700-2200m (inversion) then sharply. pm Temperature Gradient Inversions 957 1452 2342m 1.3o. Overall gradient 78-2304m 5.2oC/km Relative Humidity falls off from 2300m (inversion). NO2 falls from surface to 100m then zero. O3 rises fairly steadily from surface to 3000m. OXICOA Flights 1996 Variation of Logged Parameters During Traverses 19.7.96 150m Traverse 21 min 600m Traverse 28m Mean SD RSD% Mean SD RSD% Altitude 152.1 6.3 4.1 613.9 7.7 1.3 Air Temp 20.4 1.0 4.7 17.7 1.4 7.8 Ozone 74.1 3.9 5.3 75.9 8.2 10.9 NOx 3.2 1.6 48.3 3.7 4.5 122 NO2 3.51 4.8 138 5.9 12.3 208 Wind Dir/Speed 177/5 216/2 262/4 Wind Dir/Speed 182/8 206/6 208/0.5 224/7 205/5 196/9 190/7 185/6 24/7/96 150m Traverse 22min 600m Traverse 11.40-12.07 Mean SD RSD% Mean SD RSD% Altitude 151.3 8.0 5.3 605 7.4 1.2 Air Temp 15.2 0.5 3.1 12.2 0.9 7.1 Ozone 37.7 0.6 1.65 37.9 0.7 1.9 NO2 0.25 0.03 14.0 0.25 0.03 14.0 Wind Dir/Speed 323/10 327/8 329/7 Wind Dir/Speed 344/7 349/8 322/15 335/13 350/5 330/7 331/8 321/5 Profile Ascents and Descents on the 16th 19th 23rd and 24th July a total of 22 controlled rate ascents and descents were made, mostly between 150 and 2750m, to characterise the vertical structures of the atmosphere in temperature and composition. The data, except for winds, has been sent to the database and copies of the pilot's logs containing the wind data have been sent to the Mace Head campaign organizers. It is difficult to see how the profile data could be summarised within the compass of this report but a separate report will be prepared if there is a feeling among the other investigators that it should be. 23rd July - Comparison of the Three Flights Profile Wind Statistics Direction Speed (ms-1) Mean SD RSD% Mean SD RSD% Flight/Profile 1,1 325 8.9 2.7 10 3.0 15.2 1,2 320 12.9 4.1 9 3.8 21.2 2,1 321 18.8 5.9 9 4.3 23.7 2,2 318 12.0 3.8 8 2.2 13.6 3,1 309 19.0 6.1 9 3.8 21.9 3.2 310 12.0 3.9 8.5 3.9 23.5 On the whole the conditions were fairly constant, as might be expected in an on-shore wind. Some other Characteristics of Profiles 16th 19th & 23rd July 16th July 2 ascent/descent pairs about half an hour apart Air temperatures very similar with a hold at about 900m and at 1500-2200m Ozone profiles very similar 57-85ppb in first 800m, fall back to 52 800-1800m, mostly above 1600m. Low values 2500-2800m NOx max at 600m then drops toward 1500m, NO zero NO2 max at 600m then drops to near zero 19th July Initial profile near Galway (southerly wind), descent to low altitude off Mace Head then shorter profile near Galway. Galway profiles affected by emissions from there, descent the only reliable marine one. Air temperatures - 1st and 3rd profiles nearly identical with an inversion 1o at 700m and a hold at 2000m. Descent has pronounced inversion 800-1000m 4o and temperature below this 5oC below the other profiles. All three similar above the 700m inversion. Ozone - Galway profiles have large upward break at 1000m with a maximum at 1400m then a decrease. Descent (marine air) fairly constant up to 2000m then falls. Descent about 15ppb above the Galway ascents (75 against 60ppb) at the lowest levels. NO2 - descent starts at about 1ppb at lowest level, 2nd Galway ascent starts very high and must have registered emissions from there. All converge on zero above 2000m. 23rd July Air Temperatures - inversions 1o between 1300 and 1800m. Temperature levels very similar in all three flights. Ozone - increase from 0-700m then levels off then falls off 1500-1700m. Fall most pronounced in first flight and non-existent in second. Sharp increases above 1700m and 2500m all flights. First flight levels lower by about 5ppb than the other two which were very similar. At lowest altitude 30ppb first flights 40-45 2nd and 3rd. NO2 first flight 0.5 ppb at 1500m rising to 1.5ppb at 2700m. High Altitude Flight (DOAS Nitrate Measurement Context) 17th July The aircraft took off from Galway at 6am (GMT) and climbed to 7772m (25500ft) at 305m/min (1000ft/min) near Mace Head, then descended at 150m/min (500ft/min) and returned to Galway, landing at 8am. Holds for collecting air samples were made at the top of the climb and at 10000, 6000, 5000, 4000, 3500, 2000 and 1000ft. Sunrise would have been at about 5.45 GMT at the longitude of the flight. The sky was clear with haze below about 1060m (3500ft). The air temperature record indicated an inversion starting at about 1300m during the ascent and about 1100m on the return. Winds were recorded as 095o 7ms-1 at 500ft 146o 4ms-1 at 1000ft to 274o 9ms-1 at 25500ft. The main interest in the gas measurements (ozone and nitrogen oxides) lay in the apparently pronounced ozone layer structure and the indication of surprising concentrations of NO2 at high altitudes. There are uncertainties about the calibrations of the gas instruments under the circumstances of this flight. On examination it appears that the structure seen in the ozone profiles is not an artifact of for instance the pressurisation changes which had to be made. Similarly the NO2 profile in turn is not a reflection of the influence of the highly structured ozone. So the general characteristics of the profiles are acceptable. A comparison was made of the values of the photostationary ratio [NO][O3]/[NO2] calculated from the NO (from NOy), NO2 and ozone concentrations, the ratio derived from the JNO2 instrument responses and the theoretical values calculated from the known energy output of the sun in the relevant wavelength range. The theoretical values are higher than the mean JNO2 values by perhaps 2 ppb. The values derived from the chemical measurements remains at the level of the lowest JNO2 values. Any further possible modifications of the calibrations would make the disagreement greater. We cannot therefore make a more positive statement about the rather strange gas concentrations beyond saying that the effects we have seen are real, but the evidence is that there were elevated concentrations (several ppb) of NO2 at high altitudes. A first attempt at modelling the formation of the nitrate radical showed peaks of several hundred ppt at low altitudes (about 2000m) and concentrations falling very low at high altitudes with N2O5 (ppb levels) then dominating. The high altitude effect is thought to be due to the slowing of the reactions at the low temperatures there. Acknowledgements Thanks must be given to our colleague Dr. Roy Colvile and our former colleague Dr G.M. Glover who acted as second observers during the campaigns in what was at times an extremely frustrating operation when almost nothing seemed to be willing to work. I must also thank our aircrews, especially the pilot Mr Roger Bailey but also the 1996 co-pilot Mr Serge Fink who went far beyond the requirements of their functions to help to keep us going. We are also indebted to the whole staff of Galway airport for the helpfulness and tolerance of us during our five week stay in 1996.