REM12-2.indb

Radiation Environment and Medicine 2023 Vol.12, No.2 91–98

Regular Article

Anytime that someone travels by air they will receive a dose of ionising radiation in the form

of cosmic radiation. The aim of this study was to estimate the average dose of cosmic radiation

received by a member of the Irish public over the period of a typical year due to air travel. The

frequency of air travel by Irish residents to several regions was determined using data from

various sources. The total dose that one would receive for a typical flight to and from the region

was then calculated using software available for flight crews to estimate the radiation dose that

they have received through flying. The annual effective dose for an Irish person as a result of

cosmic radiation from air travel was estimated to be 68

Sv.

Key words: cosmic radiation, EPCARD, dose assessment, air travel, public exposure

The Estimation of Annual Exposure to the Irish Population

from Cosmic Radiation due to Air Travel

Fergal Dolan

* and Kevin Kelleher

2, 3

University College Dublin, Belfield, Dublin 4, Ireland

Associate Research Professor , Institute of Radiation Emergency Medicine, Hirosaki University, Japan

Environmental Protection Agency, Richview, Dublin 14, Ireland.

Received 20 August, 2022; revised 15 January, 2023; accepted 23 January, 2023

*Fergal Dolan: University College Dublin, Belfield, Dublin 4, Ireland

E-mail: [email protected]

https://doi.org/10.51083/radiatenvironmed.12.2_91

1. Introduction

Cosmic radiation is the term used to describe both the

high-energy, charged particles of extraterrestrial origin

that strike the earths atmosphere (primary particles), as

well as the secondary reaction products that result from

the interaction of those high-energy, extraterrestrial

particles with the nuclei of atmospheric constituents

(secondary particles)

.The intensity of exposure from

cosmic rays is strongly dependent on altitude and there is

also a dependence on latitude but that is less significant

Cosmic radiation is a source of ionising radiation at all

altitudes, but because the intensity of cosmic radiation

increases with increasing altitude, aircraft passengers

and crew are subject to higher rates of cosmic radiation

exposure compared to cosmic radiation exposure at

ground level

. The goal of this study was to estimate the

average radiation dose received by a member of the Irish

public due to air travel over the course of a typical year.

This study was conducted as part of a larger

assessment, which is currently ongoing as of early 2023,

with the goal of estimating the annual effective dose

of the typical Irish person from all sources of ionising

radiation. Despite the fact that estimations of annual

effective dose from cosmic radiation due to air travel have

been made before, it was deemed necessary to conduct a

new study due to changes in the flying habits of the Irish

population and changes in flight patterns in the period

since the previous studies were conducted.

2. Methods

2.1. Travel Statistics 2019

The Central Statistics Office (CSO) is Ireland s national

statistical office whose purpose is to publish detailed and

accurate statistics about Ireland s people, society and

Fergal Dolan et al. / Radiation Environment and Medicine 2023 Vol.12, No.2 91–9892

economy

. The CSO publishes data on the frequency

of international trips undertaken by Irish residents.

This data is collected by the CSO via a household travel

survey

. The data is categorised by the frequency of

travel to several discrete regions and is provided in tables

of data available to be downloaded or viewed on the CSO

website

4-6)

. The CSO data provides information on the total

number of Irish residents who have visited each of the

regions each year, but they do not distinguish between

different modes of transport.

Due to its status as an island, international travel from

Ireland must take place either via sea or via air (excluding

Northern Ireland but there are no regularly scheduled

flights to Northern Ireland from Ireland). The CSO also

publishes data on maritime travel from Ireland

. The

only regions that regularly receive maritime passengers

from Ireland are Great Britain, France and Spain

. Data

on the number of visitors who arrived in the UK by

sea in 2019 is provided by VisitBritain

. Since there are

no regular maritime passenger services from Ireland

to Northern Ireland it was assumed that all of these

maritime passengers travelled to Great Britain. Data on

the number of Irish residents who visited France by sea

in 2019 was acquired using CSO data on total outbound

maritime passengers

. It was assumed in this study

that 50% of total maritime passengers who travelled to

France from Ireland were visitors to France who were

resident in Ireland. Maritime travel to Spain from Ireland

was negligible compared to the overall number of Irish

residents who visited Spain in 2019. Using the data on

maritime passengers available and the assumptions

outlined above, data on the number of visitors who

travelled to Great Britain and France by air could be

calculated by subtracting the assumed number of

maritime passengers from the total visitor figures given

in the CSO data on Irish visitors to these regions

. For all

other regions it was assumed that 100% of Irish visitors to

the region travelled there by air.

The regional breakdown of places visited by Irish

residents provided by the CSO was, for certain regions,

not sufficient for the purposes of this study. This occurred

when the region was large, members of the Irish public

were flying to numerous destinations within these regions

or there was large variability in the radiation dose that

one would receive from flying to the different destinations

within a region. The regions identified as having this

issue were Spain and North America.

The CSO data only provides information on the total

number of visitors to Spain and does not provide any

information on the distribution of visitors between the

different regions within Spain, there is no indication of

whether a visitor to Spain travelled to mainland Spain

(including the Balearic Islands) or the Canary Islands

This is an issue because the Canary Islands receive

a relatively large number of Irish visitors

and there

is a significant difference between the dose received

from a flight from Ireland to one of the Canary Islands,

off the coast of west Africa, compared with a flight

to a destination within mainland Spain including the

Balearic Islands. Assumptions were made by looking

at data published by the CSO and comparing the total

number of passengers that travelled from Dublin airport

to each of the airports in Spain for which direct flights

were available

. Only flights from Dublin airport were

investigated because it handled the vast majority (86%) of

Irish aviation passengers in 2019

. It was thus assumed

in this study that 76% of visits by Irish residents to Spain

were to the mainland or the Balearic Islands, while 24%

were to the Canary Islands. Assumptions about the

distribution of trips to North America were also made

using the same method utilising this data from the CSO

The North American region consists of the US and

Canada and for this region it was assumed that 63% of

trips by Irish residents were made to the Northeast, 9% to

the Southeast, 15% to the Midwest and 13% to the Western

region of North America. This assumption is based on

CSO data on the number of passengers who flew direct

from Dublin Airport to the international airports within

these regions

For all European and North American regions, to

choose a representative destination for each region, the

aforementioned CSO data on total passenger numbers

was used

. The aim in choosing a representative

destination for each region was to have a destination

for which a dose estimation could be made for a return

flight between Dublin and that destination. This dose

would then be assumed to represent a typical dose for a

visitor flying to and returning from the region in which

the representative destination was located. In most

cases the destination within a region which received the

highest volume of passengers from Dublin airport on

direct flights in 2019 was chosen as the representative

destination for that region. If the destination which

had received the highest volume of passengers was

considered unrepresentative due to its geographical

location, then a different destination which had still

received a high volume of passengers but was located in

a more representative location within the region would be

chosen. For example, within mainland Spain including the

Balearic Islands, the three locations which received the

highest volume of passengers from Dublin Airport in 2019

were: Malaga with 329,649 passengers, Barcelona with

320,048 passengers and Madrid with 273,035 passengers

Both Malaga and Barcelona are located at or near the

edge of mainland Spain, with Malaga being located near

the Southern tip of Spain and Barcelona being located

in the Northeast. That is why, despite receiving less

passengers from Dublin Airport than both Barcelona and

Fergal Dolan et al. / Radiation Environment and Medicine 2023 Vol.12, No.2 91–98 93

Malaga in 2019, Madrid was chosen as the representative

destination for mainland Spain including the Balearic

Islands. This was due to it being located relatively

centrally between the two locations which received the

highest volume of passengers from Dublin Airport in 2019

while also having received a relatively large number of

passengers from Dublin Airport itself.

In the case of the Africa, Asia, Oceania and Other

America regions there were little or no direct flights to

most destinations within these regions. As a result of this,

there was not enough data from the CSO publication of

passenger numbers to choose a representative destination

using the method that had been used for the regions

within Europe and North America. In the case of Africa,

Nairobi was chosen as the representative destination

due to its location in the centre of the continent. There

was no data available on the number of Irish visitors

to different regions within Africa, so it was assumed

that the distribution of Irish visitors was uniform

throughout the continent. The Other America region

consists of all of the other countries in the Americas not

previously mentioned. Buenos Aires was chosen as the

representative destination of this region due its size and

its relatively central location within the region as there

was no data available on the frequency of Irish residents

trips to Central and South America by region. Sydney was

chosen as the representative destination for the Oceanic

region due to it being the largest city in the region

10)

and it is located relatively centrally within the region.

Bangkok was chosen as the representative destination

for Asia due to its size and its central location within the

Asian continent.

2.2. Dose Estimation

The average dose received by a visitor to each of the

regions was determined by the dose one would receive as

a result of flying from Dublin Airport to the representative

destination of the region and back again. The calculations

were made using the European Program Package for

the Calculation of Aviation Route Doses (EPCARD)

software

11)

. The EPCARD software is a tool that calculates

the dose received on a flight once specified parameters

are input. It has been approved for official dose calculation

for flying personnel by the German Federal Aviation

Authority

12)

. It has also been approved by the European

Commission for use in estimating occupational radiation

exposure of aircrew

13)

. EPCARD requires the following

input parameters to make a dose calculation: the date of

the flight, the departure airport, the destination airport,

the ascending and descending times and the cruising

altitude. Estimations for the return trip doses were made

by taking the sum of the outbound and return flight

average doses. The average doses for the outbound and

return flights were estimated by making an EPCARD

calculation for each flight with the date set as the 15th

day of each month of the year and getting the average

value by taking the sum total of all the doses for each of

the 12 months and dividing this by 12. This was done to

account for variations in the cosmic ray flux throughout

the year

14)

. Dublin airport is by far the busiest airport

in Ireland, it handled 86% of total Irish commercial air

passengers in 2019, so it was used as the departure airport

for all dose calculations

9, 15)

. The destination airport was

taken as the primary international airport within the

representative destination of each region.

The ascending and descending times and the cruising

altitudes were chosen based on the categorization of the

flight into one of three categories: short-haul, medium-

haul or long-haul. Flights under 3 hours were considered

short-haul, flights between 3-6 hours were considered

medium-haul and flights over 6 hours were considered

long-haul for this study

16)

. For short-haul flights, the

ascending and descending times were taken as 20 minutes

respectively and the cruising altitude was assumed to be

36,000 feet. For medium-haul flights, the ascending and

descending times were taken as 25 minutes respectively

and the cruising altitude was assumed to be 38,000

feet. For long-haul flights, ascending and descending

times were taken to be 30 minutes respectively with an

assumption that the plane would be at a cruising altitude

of 37,000 feet 50% of the time and 41,000 feet for the other

50%

17)

. Flight times were taken from online flight time

calculators

18, 19)

. The travel statistics from Table 1 were

then used to find the collective dose (manSv) for each

region. This was achieved by multiplying the return dose

that was estimated using EPCARD by the number of

visitors to each region.

3. Results

The number of visitors from Ireland by air to each region

considered as part of this study in 2019 are outlined in

Table 1.

The return trip dose and collective dose for each region

considered as part of this study is outlined in Table 2.

The total collective dose for all of the flights over a year

was 334 manSv. Dividing this by the population of Ireland

in 2019, which was 4,921,500, gives an annual effective

dose of 68 µSv. In 2019 there had been a 26% increase in

international trips by Irish residents since the most recent

study on cosmic radiation exposure due to air travel in

Ireland that had been conducted previously

14)

4. Discussion

Due to the covid-19 pandemic, air travel in Ireland

decreased dramatically during the years 2020 and 2021

20)

so the average radiation dose received during these

Fergal Dolan et al. / Radiation Environment and Medicine 2023 Vol.12, No.2 91–9894

Table 1.

Number of trips by air by Irish residents to the representative destinations of the regions in 2019

Region

Representative destination Return trips (1000s)

Austria Vienna 89

Belgium Brussels 99

Germany Frankfurt 261

Spain-Mainland and Balearics Madrid 1430

Spain-Canary Islands Lanzarote 451

Spain Total 1881

France Paris 527

Italy Milan 590

Netherlands Amsterdam 205

Poland Krakow 171

Portugal Faro 522

Great Britain London 1727

Denmark/Finland/Sweden Copenhagen 83

Other EU28*

Budapest 494

Other Europe Istanbul 208

North America Northeast New York City 368

North America Southeast Orlando 53

North America Midwest Chicago 88

North America West San Francisco 76

North America Total 584

Africa Nairobi 57

Asia Bangkok 301

Oceania Sydney 73

Other America Buenos Aires 63

*EU28 includes the UK as they were still a member of the European Union in 2019

Table 2.

Return and collective dose for each region.

Region Representative destination

Return trips

(1000s)

Return trip dose

(μSv)

Collective dose

(manSv)

Austria Vienna 89 35 3.1

Belgium Brussels 99 19 1.9

Germany Frankfurt 261 24 6.3

Spain-Mainland and Balearics Madrid 1430 27 38.6

Spain-Canaries Lanzarote 451 37 16.7

Spain Total 1881 55.3

France Paris 527 20 10.5

Italy Milan 590 28 16.5

Netherlands Amsterdam 205 20 4.1

Poland Krakow 171 41 7.0

Portugal Faro 522 24 12.5

Great Britain London 1727 15 25.9

Denmark/Finland/Sweden Copenhagen 83 29 2.4

Other EU28* Budapest 494 40 19.8

EU 28 Total* 165.3

EU 27 Total 139.4

Other Europe Istanbul

208

54 11.2

North America Northeast New York City 368 142 52.3

North America Southeast Orlando 53 162 8.6

North America Midwest Chicago 88 168 14.8

North America West San Francisco 76 230 17.5

North America Total 584 93.1

Africa Nairobi 57 73 4.2

Asia Bangkok 301 140 42.1

Oceania Sydney 73 160 11.7

Other America Buenos Aires 63 95 6.0

*EU28 includes the UK as they were still a member of the European Union in 2019

Fergal Dolan et al. / Radiation Environment and Medicine 2023 Vol.12, No.2 91–98 95

Fig. 1.

Annual effective doses from cosmic radiation due to air travel

in 2005, 2012 and 2019, in

Sv.

Fig. 2.

Annual effective doses for different regions in 2005, 2012 and

2019, in

Sv.

two years would not be representative of the average

dose that one would expect to receive in a typical year.

This is the reason why data from 2019 is used in this

study, as it is the most recent year, not impacted by the

covid-19 pandemic, that representative data was available

to estimate an annual effective dose for an Irish person

as a result of cosmic radiation from air travel. Domestic

flights were not considered as part of this study. Due

to the fact that Ireland is relatively small in size, there

are very few domestic flights within Ireland. Due to the

very low frequency, low altitude and short durations

of Irish domestic flights it was deemed that domestic

flights would represent a negligible impact to the annual

effective dose calculations from air travel and they were

not included in the overall dose assessment.

The value of 68 µSv for the annual effective dose of

cosmic radiation from air travel received by an Irish

resident estimated in this study is higher than previous

estimated doses, 41 µSv in 2012 and 45 µSv in 2005, as

demonstrated in Figure 1

14, 17)

. There are a number of

potential reasons for this. Firstly, there had been an

increase in air travel between 2012 and 2019 which was

significantly greater than the increase in population

during that period, there was a 25.6% increase in

international return trips as opposed to a 7.2% increase in

population in that period

4, 14, 21)

. In addition, many of the

estimations made in this study for the dose received for a

return flight were higher than they had been in previous

studies for the same destination. This could partly be due

to variations in the intensity of the cosmic ray flux for

the years being assessed but that would be unlikely to

account for the entire increase

14)

. Most of the parameter

values used in this study were consistent with the values

used in previous studies

17, 22)

apart from the dates of

the flights and the flight times (there was also a slight

difference arising from the fact that previous studies did

not include a medium-haul flight category)

17)

. In terms of

the flight times, it is possible that reliable data was harder

to source in the past, or perhaps the shortest possible

flight time between destinations was used previously,

which would result in a lower dose estimation. The flight

time calculators used in this study gave an average flight

time based on actual flight times provided by airlines.

This flight time would be more representative of the

amount of time that people actually spent in the air, and

hence the dose they would have received, compared

to the shortest possible flight time that was used in

previous studies. There were also different representative

destinations used in this study than those that had been

used previously for certain regions, possibly reflecting

the rise and fall in popularity of international destinations

with Irish residents.

In addition, there was variability between the

distribution of passenger visits to the different regions

between this study and the previous studies. For example,

In the 2012 study there were 19,000 visits to the North

America West region

14)

. This had increased to 76,000

in 2019, a 300% increase

. North America West had the

highest estimated dose for a return visit out of all of the

regions. This was not the only example of a shift in visits

to regions with a higher return dose, North America as

a whole received a larger share of visitors in 2019 than it

did in 2012. See Figure 2.

A potential for inaccuracy in the dose estimation in

Fergal Dolan et al. / Radiation Environment and Medicine 2023 Vol.12, No.2 91–9896

this study could come from the variability in estimated

dose that could arise due to the choice of a different

representative destination. Within Europe the variability

between destinations within regions would be relatively

small and the choice of representative destination was

usually an obvious one based on passenger volume

data. Within the North American region, the passenger

volume data also allowed for a relatively well-informed

decision to be made on which destination to choose as

the representative destination. However, with the other

regions, there was limited data available to determine

the choice of representative destination. However, it is

possible to make an estimation of potential variability

between destinations within a region.

Within Asia, for example, Bangkok was chosen due to

its size, assumed popularity (no data could be found on the

actual number of Irish visitors to Bangkok) and central

location. There was no data available on the frequency

at which Irish residents to travel to different destinations

within Asia, but Dubai and Tokyo are both major Asian

cities, so the assumption could be made that they both

receive a significant number of visitors from Ireland.

Dubai is one of the closest destinations to Ireland within

Asia while Tokyo is one of the furthest Asian destinations

from Ireland. A typical return trip dose for Dubai in 2019

was estimated at 81 µSv while a dose for a return visit

to Tokyo in 2019 was estimated at 259 µSv. Comparing

these values with the return dose of 140 µSv estimated for

Bangkok in this study, it can be seen that there is quite a

large amount of variability between different destinations

in Asia. Comparing the estimated dose of 73 µSv for

Nairobi with an estimated dose of 112 µSv for a return

visit to Johannesburg, and an estimated dose of 55 µSv for

a return visit to Cairo, it can be seen that the variability

of dose between destinations within Africa is less than

the variability of dose between destinations within Asia.

This is, in part, due to the close proximity of the African

destinations to the equator, because the intensity of

cosmic radiation is lowest closer to the equator and

highest closer to the poles

23)

. Considering the relatively

low number of visitors to Africa in 2019 the uncertainty

arising from the choice of the representative destination

in the African region would be relatively small.

The dose for a return visit to Perth was estimated

at 138 µSv compared to the 160 µSv dose estimated

for a return visit to Sydney, so there is not much of a

variation between different destinations within Australia

when comparing the dose for a return trip from Ireland.

It is difficult to estimate the typical dose for a trip to

Auckland as there is a very large amount of variability

in where flights from Dublin will connect through, with

many flights from Dublin to Auckland having at least

two connections. Looking at one of these flights which

connects through San Francisco as an example, the dose

for a return trip was estimated at 305 µSv. This is much

larger than the 160 µSv dose for a return trip to Sydney.

However, it was assumed in this study that visits to New

Zealand did not make up a large portion of Oceanic visits.

In addition, total visits to Oceania were relatively small

compared to the total number of Irish outbound trips

so this variability would not have a huge effect on the

uncertainty on the total collective dose estimation for all

regions. For the Other America region, a return visit to

Havana and a return visit to Sao Paulo were estimated at

143 µSv and 89 µSv respectively compared to the value

of 95 µSv estimated for a return visit to Buenos Aires.

Once again due to the relatively low number of visits to

the region, the uncertainty to the overall estimation that

would arise due to this variability is small.

Given that the collective dose for Asia was much larger

than it was for other regions where there were similar

difficulties in picking a suitable representative destination,

the Asian region is likely to be the biggest contributor to

potential uncertainty within this study. This is because

the variability between doses flying to and from different

destinations within the region is large. Despite the fact

that the European and North American regions made

up a much greater distribution of the overall estimated

collective dose, the potential uncertainty that could arise

from these regions is lower. This is due to the fact that

there is less variability between potential representative

destinations within these regions and there is sufficient

flight data available for the European and North

American regions when compared to Asia.

It is also worth noting that since the previous dose

surveys on the annual effective dose for an Irish person

as a result of cosmic radiation from air travel

17, 22)

the EPCARD software has been updated to ensure

compliance with the latest European Basic Safety

Standards Directive

13)

, where a new methodology for

calculating doses was introduced, based on the latest

scientific evidence on radiation risks and radiation

and tissue weighting factors from the International

Commission on Radiological Protection (ICRP 103)

24)

A study by Mares et al

25)

found that the updated

radiation weighting factors recommended by ICRP 103

for neutrons, and protons results in a dose difference

of less than 8% when compared to older recommended

radiation weighing factors used in previous versions of

the EPCARD software. This change in dose per flight is

insignificant when compared to the overall dose estimated

as part of this survey.

5. Conclusion

In summary, the estimated figure for the annual effective

dose of cosmic radiation due to air travel in this study

was higher than previous estimates. In this study, the

Fergal Dolan et al. / Radiation Environment and Medicine 2023 Vol.12, No.2 91–98 97

estimated annual effective dose of cosmic radiation due

to air travel for a typical Irish was 68 µSv, compared

with an estimate of 41 µSv in 2012 and 45 µSv in 2005

14, 17)

In 2014, the overall annual effective dose of ionising

radiation received by a typical member of the Irish public

from all sources of ionising radiation was estimated to be

4,037 µSv

14)

. It can be seen from this value that cosmic

radiation exposure is not a major source of ionising

radiation when compared to other sources of ionising

radiation received by a typical person in a year. 2014 is

the most recent year that data was available on the total

dose of ionising radiation that the typical Irish person

could expect to receive in a year. The 68 µSv value for

cosmic radiation exposure in 2019 estimated in this study

would comprise only approximately 2% of the total annual

effective dose of ionising radiation a typical Irish person

would receive, assuming the total dose was similar to the

value estimated in 2014

14)

The potential reasons for the estimated annual effective

dose in this study being higher than in previous studies

include:

• An increase in per capita international air travel by

Irish residents up to 2019

• A greater proportion of international air travel

being on higher dose routes in 2019 compared to

previous years

• The fact that the flight times used in this study

were the average flight times as opposed to the

shortest possible flight times, which may have

been the flight times used in previous studies.

Longer flight times would give a higher dose as

they would lead to a greater duration of exposure

The greatest potential for uncertainty in this study is

from the estimation made for the collective dose for air

travel to Asia. This is due to the large variability in return

trip doses for different destinations within Asia, the

relatively large number of Irish visitors to this region and

because of the uncertainty in choosing the representative

destination due to a lack of available data on the number

of Irish visitors to specific locations in Asia.

Declaration

The authors declare that they have no conflict of interest.

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