Recent trends in cosmic radiation exposure onboard aircraft: effects of the COVID-19 pandemic on Japanese in-flight doses

Abstract

Background: Galactic cosmic radiation (GCR) is a naturally occurring environmental radiation that originates from outer space. GCR is modulated by solar activity, and its intensity increases with increasing geomagnetic latitude and altitude, reaching a peak of up to approximately 20 km in the atmosphere. Therefore, commercial flight passengers (flyers) are exposed to elevated levels of cosmic radiation while flying onboard commercial aircraft. Although the recent COVID-19 pandemic, which began in early 2020, is believed to have significantly affected public exposure to cosmic radiation, this impact is yet to be quantified.

Methods: Based on the official records of Japanese flyers, their annual per-capita doses (APCDs) of cosmic radiation exposure on international and domestic flights were calculated using the established code JISCARD EX over a 7-year period from 2014 to 2020 (including the first year of the pandemic). For estimating the APCDs on international flights, the world was divided into eight regions. The aviation route dose to a representative city in each region was determined at three cruising altitudes: 34,000 ft. (10.4 km), 37,000 ft. (11.3 km), and 40,000 ft. (12.2 km).

Results: At a typical cruising altitude of 37,000 ft., the flyer-average APCD from international flights was estimated to be approximately 60 μSv y^-1, while the APCD from domestic flights was approximately 2 μSv y^-1 over the target period, including the pandemic year (2020). These results indicate that the distribution of Japanese travel destinations did not change significantly during the pandemic period. In contrast, the population-average APCD significantly decreased from approximately 10 μSv y^-1 in the pre-pandemic period (2014-2019) to 2 μSv y^-1 in 2020, representing a reduction of more than 80%, which corresponds to a decline in the number of travelers.

Conclusion: The results of this study indicate that the population-average APCD of Japanese flyers decreased significantly during the COVID-19 pandemic, while the flyer-average APCD remained largely unchanged. Further studies will be performed to determine APCDs for the subsequent period and to assess the overall effect of the pandemic on public health.

Keywords: COVID-19 pandemic; Japanese; aviation dose; commercial flight; cosmic radiation; per-capita.

Figure 1

Changes in the monthly and yearly average heliocentric potentials (HPs) over 7 years from January 2014 to December 2020 (21), which were used to calculate the in-flight cosmic radiation doses of flyers in this study.

Figure 2

Annual numbers of international air travel by Japanese travelers from 2014 to 2020, classified by eight destination regions (22).

Figure 3

Locations of the cities selected as destinations representing the eight regions used to calculate aviation route doses in international flights from Japan.

Figure 4

Time changes in the flying altitude of commercial aircraft during four international flights from Japan [reproduced from the data published by Yasuda et al. (26)].

Figure 5

The three flight routes employed for the calculation of aviation route doses from domestic flights in Japan; a unit-distance route dose was determined from these three routes and applied to the calculation of collective doses.

Figure 6

Calculated aviation route doses for round-trip flights to the cities representing seven out of the eights regions (Figure 3) at three cruising altitudes (34,000, 37,000, and 40,000 ft) as a function of flight time for 2014 (a) and 2018 (b).

Figure 7

Calculated flyer-average per-capita doses (APCDs) for Japanese flyers from cosmic radiation during international flights for the period 2014–2020.

Figure 8

Calculated annual per-capita doses (APCDs) as the Japanese population average from cosmic radiation during air travels for the period of 2014–2020.

Figure 9

(a) Locations of the three cities in the United States (Los Angeles, Houston, and New York) and (b) calculated route doses from Tokyo to the three cities when flying in November 2020 at constant cruising altitudes of 34,000, 37,000, and 40,000 ft. The dotted lines in the map (a) indicate great circle routes from Tokyo.