Each campaign consists typically of 4 flights, connecting Novosibirsk and Yakutsk and back. A series of ~26 vertical profiles are collected during each campaign. Each profile takes about 30 minutes, including horizontal plateaus at 0.5 and 7 km, and at 5 km on descents.

The flights are performed in all-weather conditions, and flight pattern may be altered to avoid large clouds. The times of flights were dependent on logistical constraints. The long duration of the flights allowed sampling a large diversity of combinations of air masses, cloudiness conditions, solar zenith angles and vegetation cover types. Diurnal variations of the BL height are expected to affect the comparability of individual profiles, but these differences tend to compensate over a whole flight, when making composite profiles.

The chartered aircraft is a Tupolev 134 with twin jet engines on the rear, with cruise speed of 850–900 km/h and a range of 1900–3000 km.

The former aircraft was a two-propeller Antonov-30 operated by the Institute of Atmospheric Optics of Tomsk (Zuev et al., 1992). The maximum range of the aircraft is 3400 km and its airspeed during measurement is about 85 m s^-1. Vertical speed during vertical profiles is about 3.5 m s^-1 on ascent and 7 m s^-1 on descent.

In 2012, a Picarro G2301-m instrument has been purchased to measure CO₂ and CH₄ [ link ] during the next campaigns. Here, concentrations are measured using the Cavity Ring-Down Spectroscopy (CRDS) technique. The instrument measures CO₂, CH₄ and water at a 1-HZ measurment rate with ppb sensitivity. The instrument also includes water correction software. According to manufacturer specifications, the precision is 0.2 ppm CO₂ and 1.5 ppb CH₄.

Until 2011, the CO₂ analyser is a Li-Cor 6262 modified non-dispersive infrared (NDIR) analyser modified at the LSCE. The Li-Cor is embedded in a system which regulates the temperature, flow and pressure of incoming air. Sampled air is dried upstream using magnesium perchlorate. Pressure fluctuations within 0.5 mbar around target value pressure are allowed in the data processing. Acquisition frequency is 0.5 Hz.

In-flight calibrations are performed at 30 minutes intervals using three calibration gases. These gases are carried in high-pressure cylinders that are used sequentially (“high”, “low”, and “reference” value). Their values were determined at the LSCE laboratory prior to shipment and are traceable to a suite of primary WMO-CO₂ standards from NOAA/ESRL. The concentrations used are 370.60±0.01, 380.47±0.01 and 409.76±0.01 ppm respectively. The three calibration gases are analyzed during the flight at ~30min intervals. The drift is corrected for based on errors in estimation of reference gas. During the April 2006 campaign, the precision was 0.4 ppm and accuracy 0.15 ppm. Improvements in the electronics yielded a precision of 0.15 ppm for subsequent campaigns. The CO₂ instrument precision is estimated from the standard deviation of the stabilized concentration signal during 1 minute after injecting the reference gas, allowing 2 minutes for stabilization in the measurement cell. The accuracy is estimated as the offset of the instrument when measuring a ‘target’ reference gas cylinder during 1-min in the pressure-stabilized cell. The CO₂ data are processed using a semi-automatic filter based on pressure, flow and temperature in the measurement and reference cells of the Li-Cor.

Instrument PI: Jean-Daniel Paris

The O₃ analyser is developed from a commercial fast response ozone analyser (Thermo Instruments Model 49), with modifications for internal calibration and aircraft operation safety. The instrument is based on classic UV absorption in two parallel cells (zero, sample), with a precision of 2 ppb, 2% for an integration time of 4 sec. It is compensated for aircraft pressure and temperature variations. Prior to detection, air is pressurised to cabin pressure, using a Teflon KNF Neuberger pump model N735 also used for the CO instrument. Electrical improvements has been brought by Laboratoire d’Aérologie, including a 27VDC supplied power provided also to the CO instrument. For the YAK-AEROSIB project, the ozone instrument includes a specially designed computer for data acquisition and for instrument control, powered in aircraft 27VDC. Before shipping to Russia, the O₃ analyser has been calibrated against a NIST related reference calibrator Model49PS. A calibration box with an O₃ generator is used for laboratory verifications of the ozone analyser before and after the campaigns.

Instrument PI: Philippe Nédélec

The CO analyser has been described in Nédélec et al. (2003). It is a fully automated instrument designed to reach an accuracy of 5 ppb or 5%. The instrument is based on a commercial infrared absorption correlation gas analyser (Model 48C, TEI Thermo Environment Instruments, USA). The model 48CTL is qualified by U.S. EPA designated method EQSA-0486-060. Laboratoire d’Aérologie improved the instrument accuracy with addition of periodical (every 20 minutes), in-flight accurate zero measurements, new IR detector with better cooling and temperature regulation, pressure increase and regulation in the absorption cell, increased flow rate to 4 l/min, water vapour trap and ozone filter. The precision achieved for 30 seconds integration time (corresponding to the response time of the instrument) is 5 ppb or 5% CO, with a lower detection limit of 10 ppb.

Instrument PI: Philippe Nédélec

Temperature, humidity and wind vector are measured routinely onboard using HYCAL sensor model IH-3602-C of Honeywell Inc. Temperature range is from -70 to +70°C and accuracy is 0.5°C. Relative humidity range is from 0 to 100% and accuracy is 7%.

Instrument PI: Mikhail Arshinov

Ultra fine particles concentration in the diameter range from 3 to 200 nm are measured using an 8-channel automated diffusion battery (ADB; designed by ICKC SB RAS, Novosibirsk; Reischl et al., 1991; Ankilov et al., 2002a, 2002b) coupled to a condensation particle counter (Arshinov and Belan, 2004). Air is sampled using a quasi-isokinetic inlet (Zuev et al., 1992) at the front side of the aircraft. The ADB system has been specially designed for airborne applications with regulated flow rate, compensating for outside pressure variations and minimising particle losses. In order to reduce integration (scanning) time and hence improve precision, only two channels of the battery are used in the instrument. This also improves the total particle concentrations retrieval. Size response of the instrument is homogeneous over the 3–200 nm size range (Ankilov et al., 2002b) and for different aerosol compositions. Transmission efficiency for the airborne instrument is corrected for and is ~0.997 in the 70–200 nm range and between 0.82 at 400 hPa and 0.89 at 1000 hPa for the 3–70 nm size range. All concentrations are reported at standard pressure and temperature (STP) conditions.

Instrument PI: Mikhail Yu. Arshinov

Equivalent black carbon (EBC) mass concentration are measured using an aethalometer based on diffuse attenuation of light by particles after collection on a filter (Panchenko et al., 2000). The wavelength ranges between 0.4 and 1.1 µm with maximum near 0.9 µm. This instrument is sensitive to submicron particles. EBC mass concentration MBC is converted from light absorption. The sensitivity of the aethalometer is ~0.01 µg m-3 EBC.

Instrument PI: Mikhail V. Panchenko

Particle concentrations in 15 size bins in the range 0.3 – 20 um were measured using a GRIMM 1.108 instrument (GRIMM Aerosol Technik GmbH & Co. KG, Germany).

Instrument PI: Mikhail Yu. Arshinov