Atmospheric Ionizing Radiation from Galactic and Solar Cosmic Rays

Abstract

An important atmospheric state variable, driven by space weather phenomena, is the ionizing radiation field. The two sources of atmospheric ionizing radiation are: (1) the ever-present, background galactic cosmic rays (GCR), with origins outside the solar system, and (2) the transient solar energetic particle (SEP) events (or solar cosmic rays), which are associated with eruptions on the Sun’s surface lasting for several hours to days with widely varying intensity. Quantifying the levels of atmospheric ionizing radiation is of particular interest to the aviation industry since it is the primary source of human exposure to high-linear energy transfer (LET) radiation. High-LET radiation is effective at directly breaking DNA strands in biological tissue, or producing chemically active radicals in tissue that alter the cell function, both of which can lead to cancer or other adverse health effects (Wilson et al., 2003; 2005b). Studies of flight attendants have suggested adverse reproductive health outcomes (Aspholm et al., 1999; Lauria et al., 2006; Waters et al., 2000). The International Commission on Radiological Protection (ICRP) classify crews of commercial aircraft as radiation workers (ICRP, 1991). The US National Council on Radiation Protection and Measurements (NCRP) reported that among radiation workers monitored with recordable dose, the largest average effective dose in 2006 (3.07 mSv) was found in flight crew. In contrast, the average for the workers with the second largest effective dose, commercial nuclear power workers, was 1.87 mSv (NCRP, 2009). However, aircrew are the only occupational group exposed to unquantified and undocumented levels of radiation. Furthermore, the current guidelines for maximum public and prenatal exposure can be exceeded during a single solar storm event for commercial passengers on intercontinental or cross-polar routes, or by frequent use (∼ 10-20 flights per year) of these high-latitude routes even during background conditions (AMS, 2007; Copeland et al., 2008; Dyer et al., 2009).