Balloon Flight and Atmospheric Conditions Analysis

The balloon was filled with helium, and its position was tracked by APRS-supported services: www.habhub.com and www.aprs.fi. The telemetry was emitted through RTTY 70 cm/APRS 2 m signal, supported with a GPS/GSM tracker. On-board computer (ATMEGA328P) was equipped with sensors located at the top wall [for UV radiation (ML8511), pressure (BMP085), and temperature (DHT22) measurements], additional UV sensors at the side wall of the gondola, and accelerometer (MPU6050) inside the box. To compare stratospheric and Earth UV irradiation, the UV ML8511 sensor was used—designed especially for surface measurement of UV spectra [UVA (280–400 nm) and UVB (260–280 nm)]. As it is mentioned in the specifications, this sensor has a nominal operation range of −20–70°C, suggesting that the monitoring of UV would only be valid up to roughly the minute 30 of the flight. This means that some of the random variations depicted in Figure 1E may be an artifact of the electronics, which is not operating adequately at such low temperatures. The electronic devices oftentimes produce too much noise when going below certain temperature thresholds and furthermore being exposed to moisture freezing. However, ground analyses displayed that after recalibration, the sensors may be used in temperatures below −20°C, which caused insignificant disturbances of measurements.

The biological samples were launched to the stratosphere on the 30th of April 2018, from Wrocław, Poland (51°06′23.6″ N 17°03′32″ E) at 11:30 am. The balloon reached the stratosphere at maximal altitude of 30,298 m. The mission lasted ∼2 h: 90 min of ascent and 25 min of descent; ended at 1:25 pm. The biological samples were collected immediately after landing in Sulisław, Poland (52°23′49.9″ N 18°45′52.8″ E) and transported directly to the laboratory. During the first stage of ascending phase, recorded ambient temperature dropped to −22°C. Subsequently, when the balloon reached the ozonosphere, the ambient temperature increased to −2°C. At the highest altitude, the temperature reached the lowest level of −35°C ( Figure 1C ), and the lowest pressure (1,252 Pa) was measured ( Figure 1D ). Data provided by two UV sensors showed that the top and side walls of the gondola were similarly exposed to the UV radiation during the balloon ascent. However, during the balloon descent, there was a difference observed between the measured UV radiation on both sides of the gondola, caused by continuous rotations of the gondola in the last stage of the flight. ( Figure 1E ). Voltage level of 1,170 mV correlates with the highest score (11) in the UV Index exposition scale, which shows extreme exposure to the UV radiation, causing immediate damage of unprotected human skin and eyes (Fioletov et al., 2010). On the right side of the chart, there is a clearly visible period measured by the first UV sensor when the parachute was opened; as a result, the gondola was stabilized. In the upper parts of the atmosphere, the UV dose was more than twofold the dose correlating with the maximum dose in the UV Index scale (reaching nearly 2,463 mV).