ORIGINAL PAPER

An estimation of Canadian population exposure to cosmicrays from air travel

Jing Chen • Dustin Newton

Received: 8 August 2012 / Accepted: 28 October 2012 / Published online: 9 November 2012

� Her majesty the Queen in Right of Canada 2012

Abstract Based on air travel statistics in 1984, it was

estimated that less than 4 % of the population dose from

cosmic ray exposure would result from air travel. In the

present study, cosmic ray doses were calculated for more

than 3,000 flights departing from more than 200 Canadian

airports using actual flight profiles. Based on currently

available air travel statistics, the annual per capita effective

dose from air transportation is estimated to be 32 lSv for

Canadians, about 10 % of the average cosmic ray dose

received at ground level (310 lSv per year).

Keywords Cosmic rays � Annual effective dose �Population exposure

Introduction

Everyone is exposed to ionizing radiation from natural

sources. There are two main contributors to natural radia-

tion exposures: high-energy cosmic ray particles incident

on the Earth’s atmosphere and radioactive nuclides that

originate in the Earth’s crust and are present everywhere in

the environment. Background radiation levels in the atmo-

sphere are generated primarily by galactic cosmic rays.

There are two major effects that shield against primary

cosmic radiation, namely the Sun’s and the Earth’s mag-

netic fields. Entering the solar system, the fluence of cosmic

rays is modulated by the periodic solar activity: The Sun

emits a huge flow of matter known as solar wind which has

to be overcome by the primary particles (predominantly

protons). The intensity of the solar wind fluctuates

depending on solar activity, which can be deduced from the

number of sunspots, with a cycle of 11 years. The shielding

effect of the Sun is smaller during the period of solar

minimum activity. When approaching the Earth, the cosmic

rays are deflected by Earth’s magnetic field acting as cutoff

in their energy spectra. It is easiest to overcome this field at

the magnetic poles because the particles there run roughly

parallel to the magnetic field lines. In contrast, at the geo-

magnetic equator, the particles need to have much higher

energy (over 15 GeV) to cross perpendicularly the magnetic

field lines and enter the Earth’s atmosphere. Since the far

more frequent lower-energy particles are deflected away

from the Earth, radiation exposure is lower at the equator

than at the poles. Thus, the fluence of the primary particles

is a function of the time in the solar cycle and of the location

in the geomagnetic field. Interaction of these primary par-

ticles with the atoms in the atmosphere results in a complex

field of secondary cosmic radiation which for example

includes neutrons, protons, pions, photons, electrons, and

muons. A comprehensive review of worldwide exposure

from natural sources was given by the United Nations

Scientific Committee on the Effects of Atomic Radiation

(UNSCEAR) in its 2000 report (UNSCEAR 2000). It was

estimated that worldwide exposure to cosmic radiation

results in an average annual effective dose of 0.38 mSv.

This estimate is for exposure to cosmic rays at ground level

by applying the indoor shielding factor of 0.8 and assuming

indoor occupancy to be 80 % of time.

It is well understood that exposure to cosmic rays

increases strongly with altitude and somewhat less with

latitude. When traveling at commercial aircraft altitudes,

one could receive a significantly higher radiation dose than

that at sea level. In addition, the radiation exposure at a

given flight altitude increases two to three times from the

J. Chen (&) � D. Newton

Radiation Protection Bureau, Health Canada,

2720 Riverside Drive, Ottawa K1A 0K9, Canada

e-mail: jing_chen@hc-sc.gc.ca; jing.chen@hc-sc.gc.ca

123

Radiat Environ Biophys (2013) 52:59–64

DOI 10.1007/s00411-012-0444-7

equator to approximately 50� north or south. Thus, at high

altitude and latitudes close to the magnetic poles, such as

with some long-haul Canadian domestic and international

flights, radiation doses received during these flights would

be much higher than those received on short-haul flights at

lower altitudes and latitudes. In its report no. 94, the

National Council on Radiation Protection and Measure-

ments (NCRP) analyzed the exposure of the population in

the United States and Canada to cosmic rays, and estimated

that the average population effective dose from cosmic

radiation is 0.27 mSv per year; 0.26 mSv at ground with

consideration of altitude distribution of the population and

an additional 0.01 mSv from air travel (NCRP 1987).

Based on air travel statistics in 1984, the NCRP estimated

that less than 4 % of the population dose from cosmic ray

exposure would result from air travel.

Recently, a more accurate estimation of the exposure to

cosmic rays was conducted for more than 1500 commu-

nities across Canada (Chen et al. 2009). It was estimated

that the Canadian population-weighted average annual

effective dose due to cosmic ray exposure at ground level is

0.31 mSv, averaged over solar activity. Because the pop-

ulation-averaged occupancy time at aircraft altitudes would

only be several hours per year even with significantly

increasing air travel, the population dose from air trans-

portation is expected to remain a small fraction of that

resulting from cosmic ray exposure on the ground. In this

study, a more accurate estimation of radiation burden from

air traveling is made for the Canadian population based on

currently available air travel statistics. In addition to the

assessment of population doses from cosmic rays during air

travel, it is important to recognize that the range of indi-

vidual exposures is considerable. For radiation protection

of individual air travelers, average dose rates are also

estimated for typical Canadian domestic, transborder, and

international flights.

Methods

Estimation of doses to passengers is based on route doses

obtained from measurements or calculations of the effec-

tive dose rate as a function of flight parameters. There has

been considerable research carried out on both measure-

ment techniques and calculation methods, as summarized

in the report from the EURADOS WG5 (EC 2004). There

is general agreement between the results of experimental

determinations and computer calculations. The total

uncertainty in the values of effective dose calculated by the

different computing codes was estimated to be about 30 %,

and may extend up to 50 % if the calculations are based on

planned rather than actual flight profiles (EC 2004). The

uncertainties for the assessment of doses to air travelers

meet the accuracy requirements of the ICRP and ICRU

(ICRU 2010) when actual flight profiles are used. This

supports the approach of basing determinations of effective

dose for air travelers on the results of calculations.

There are several software packages that calculate

effective dose rates at aircraft altitudes and effective doses

to air crew or passengers, such as AVIDOS, EPCARD,

QARM, FREE, PCAIRE, and SIEVERT. The overall

agreement between the codes was generally better than

±20 % from the median (Bottollier-Depois et al. 2009). In

the present study, the software package, PCAIRE (Lewis

et al. 2005), was used. Based on over 160 in-flight mea-

surements, correlations have been developed to allow for

the interpolation of the cosmic ray dose rate for any global

position, altitude, and date. This resulted in a Predictive

Code for Aircrew Radiation Exposure (PCAIRE). The code

has been validated against the integral route dose mea-

surements made on 49 jet-altitude flights. On most flights,

the code agreed with the measured data (within 25 %). The

PCAIRE code was used online (www.pcaire.com) with

actual flight profiles available for all flights departing from

Canadian airports.

All departure flights were grouped into three categories:

domestic departures, US departures, and international

departures. With actual flight profiles available on the

Internet (details are given below), effective doses to pas-

sengers were calculated for each flight departing from a

Canadian airport. Canadian travel statistics with domestic,

transborder, and international flights were obtained from

Statistics Canada. In each category of air transportation, it

is assumed that the ratio of Canadian passengers to the total

passenger capacity applies to all flights in that category.

Assuming that all departure flights have the corre-

sponding flights arriving from the opposite direction, the

total number of flights is twice the number of departure

flights. Thus, the total population dose is twice the popu-

lation dose calculated for all flights departing from Cana-

dian airports.

Canadian airports and passenger capacities

A list of airports was taken from the commercial airports

directory provided by Wego.com (available at http://www.

wegotravel.ca/). Noticeably, absent from the list was Tor-

onto City Centre Airport (YTZ) and Arctic Bay Airport

(YAB), which were added for this study. The study list

contains a total of 259 airports in Canada. Each airport’s

Web site was visited and the departure information was

downloaded (airlines, flights, and destinations) for a single

day during the last 10 days of February 2011. In February

2011, a total of 211 airports were in operation with at least

one departure flight on the day when the Web site was

visited. For these 211 airports in Canada, there were 2,496

60 Radiat Environ Biophys (2013) 52:59–64

123

domestic departures, 608 US departures, and 178 interna-

tional departures in a single day of February 2011.

It is well known that the number of flights varies sea-

sonally. Figure 1 shows the monthly variation of air carrier

movements for domestic, transborder, and international

movements in year 2011 reported by Statistics Canada

(2012a). Based on the statistics, the numbers of air carrier

movements in February are 6.8, 7.6, and 9.1 % for

domestic, transborder, and international, respectively. To

estimate the number of departures for any day in 2011, the

above obtained daily departure figures in February are,

therefore, adjusted by a factor of 1.128, 1.009, and 0.843

for domestic, transborder, and international departures,

respectively. Annual total numbers of departure flights are

the adjusted daily departure flights multiplied by 365 days,

as shown in Table 1.

For each departure flight, the airline Web site was vis-

ited, the aircraft type used for the flight was identified, and

the capacity of the given aircraft was recorded. This was

verified with individual airlines, because not every airline

has the same aircraft configurations even though the same

equipment was used. In Table 1, the information of pas-

senger capacities is the sum of the capacities from all

individual flights for different categories at individual air-

ports in various provinces.

Air travel statistics

The above estimation is the maximum passenger capacity

for air transportation in a year. To estimate effective doses

to Canadian passengers, air travel statistics for Canadians

are needed. A summary of the statistics is given in Table 2

(Statistics Canada 2012b). In 2010, Canadians traveled

22,709,807 times domestically by air, 6,971,307 times

across the border to the US, and 8,701,172 times to

countries other than the United States.

Actual flight profiles

In order to more accurately calculate the effective dose

received by a passenger during a given flight, actual flight

parameters are needed when using PCAIRE to calculate

effective doses received during flights. These parameters

are departure date, departing airport, arrival airport, ascent

time, descent time, flight altitude, and flight time. For aFig. 1 Monthly variation of the number of departing and arriving

flights for domestic, transborder, and international flights in 2011

Table 1 Departure information obtained from 211 airports in Canada in year 2011

Province Airports in

operation

Domestic departures US departures International departures

Flights Passenger

capacity

Flights Passenger

capacity

Flights Passenger

capacity

Alberta 10 392 28,880 65 6,692 14 2,863

British Columbia 29 401 26,118 71 8,014 24 5,865

Manitoba 14 152 7,362 17 1,038 2 378

New Brunswick 4 41 1,674 2 81 0 0

Newfoundland &

Labrador

20 125 4,806 5 583 2 222

Nova Scotia 3 79 5,321 21 1,055 3 569

Ontario 40 695 42,701 314 23,211 94 18,517

PEI 1 8 291 0 0 0 0

Quebec 43 355 18,431 104 8,083 37 8,317

Saskatchewan 2 57 4,786 9 534 2 272

Three Territories 45 191 7,877 0 0 0 0

Canada (daily, Feb) 211 2,496 14,8247 608 49,291 178 37,003

Canada (any day) 2,815 167,223 613 49,735 150 31,194

Canada (year 2011) 1,027,475 61,036,395 223,745 18,153,275 54,750 11,385,810

Radiat Environ Biophys (2013) 52:59–64 61

123

given flight, the actual flight profile could vary to some

extent day by day. Since statistical results are averaged

over thousands of flights, daily variation of flight profiles

was ignored. Efforts were then focused on accurate esti-

mation of flight altitude, distance, and time.

Two Web sites were used to find all the flight infor-

mation needed to calculate the dose. The first site, Flight-

stats.com, provided all the flights departing each Canadian

airport on a given date. The total of 3,282 departure flights

from 211 Canadian airports was recorded on the Web site

for a given day in February 2011.

The data provided by Flightstats.com were not sufficient

for PCAIRE effective dose calculations. The second site,

Flightaware.com, provides real-time flight tracking. The

site provides flight information going back 7 days. After

7 days, users have to create an account, which provides

data as far back as 3 months. Each flight was searched on

this site, and data such as duration, equipment, speed,

altitude, and distance were recorded.

It is important to distinguish between direct and flown

distance. Direct distance is the distance between airports

while the distance flown is how many kilometers the air-

plane is in the air. If the flown distance is given, it was the

value recorded; otherwise, the direct distance was taken. In

most cases, the flown distances were recorded for calcu-

lating actual flight time.

Most flights on Flightaware.com include a track log

which includes the altitude and speed of the flight, updated

every minute. Using the track log, the ascent and descent

time of the flight can be determined. However, due to the

large number of flights being investigated in this study,

their ascent and descent times were not recorded individ-

ually. Instead, average ascent and descent times were cal-

culated for 10 flights in each of the 4 altitude ranges. The

averages used in the calculations are given in Table 3. A

constant flight altitude is then assumed after ascent and

before descent.

With actual flight profiles, radiation doses received by

passengers were calculated for all 3,282 flights departing

from Canadian airports in a day of February 2011.

Results and discussion

Among a total of 3,282 flights departing from Canadian

airports in a day of February 2011, flight profiles cannot be

found for some flights (\1 %) especially for very short

flights departing from airports in small communities. The

PCAIRE contains many airports in its database, but not all

of the 211 airports. Occasionally, the program cannot cal-

culate the effective dose between certain airports even

though the airport is in the database. In all those cases,

average effective doses obtained from similar flights

departing from nearby larger airports were assigned to the

flights with missing information.

Assuming the ratio of Canadian passengers to the total

passenger capacity applies to all flights in a given category

of air transportation, that is, 37.2 % for domestic, 38.4 %

for transborder, and 76.4 % for international flights (see

Table 2). Canadian annual collective dose is estimated to

be 1,076,748,198 lSv. Applying the Canadian population

of 34,126,200 in year 2010, the annual per capita effective

dose from air transportation is estimated to be 32 lSv. The

estimated annual per capita effective dose from air travel is

about 10 % of the average cosmic ray effective dose

received at ground level, which is 6 % higher than the

previous estimate made by the NCRP in 1984 (NCRP

1987). This increase is likely due to significantly increased

air travel in the past decades.

Detailed results for different categories are given in

Table 4 together with air travel statistics and estimates for

the year 2010. One can see clearly in Table 4 that more

than half of the estimated population dose due to air

transportation results from international flights.

The per capita annual effective dose is averaged over

entire populations, including non-exposed individuals.

Everyone is exposed to some level of background radiation

at ground level depending on where they live. Therefore,

for background exposure, the per capita annual effective

dose is the dose received more or less by all individuals. In

the case of air transportation, the per capita annual effec-

tive dose provides a broad indication of population expo-

sure to cosmic rays when traveling by air. However,

significant variations exist in the patterns of exposure

received by individuals. Some individuals might have

Table 2 Statistics of air travel (enplaned or deplaned) in Canada

Domestic Transborder International

Total annual capacity by

all carriers

61,036,395 18,153,275 11,385,810

All Canadian passengers

in 2010

22,709,807a 6,971,307 8,701,172

Ratio of Canadian

passengers to the

capacity

0.372 0.384 0.764

a Private communication from Don Kirkpatrick, Aviation Statistics

Centre, Statistics Canada, July 26, 2011

Table 3 Average ascent and descent time for flights at various alti-

tude ranges

Altitude (ft) Ascent time

(min)

Descent time

(min)

C35000 25 25

25,000–34,999 20 20

15,000–24,999 15 16

\ 15,000 9 10

62 Radiat Environ Biophys (2013) 52:59–64

123

multiple trips, while others might have none in a year or

none at all in their lifetime. For the purpose of radiation

protection to individuals, dose rates in the units of lSv/h

were derived for different flight durations averaged over

more than a thousand flights departing from the three

largest Canadian airports (Toronto, Vancouver, and Mon-

treal). Resulting information is summarized in Table 5.

It is well known that cosmic ray dose rates to which aircraft

passengers are exposed increase significantly with the alti-

tude. The doses to passengers depend on flight altitude and

flight time at the altitude. Short flights with durations less than

30 min normally have scheduled altitudes less than 10,000

feet, and actually only have a few minutes cruising at the

scheduled altitude. On average, the dose rate in these very

short flights is 0.4 lSv/h. Flights with longer flight time are

normally scheduled to fly between 18,000 and 38,000 feet,

and they also have longer time cruising at the scheduled

altitude. For most international flights ([3 h), the average

dose rate is 5.5 lSv/h. Based on the information given in

Table 5, individuals can estimate cosmic ray doses received

during a given flight. For example, for a traveler taking a flight

from Ottawa to Vancouver for 318 min (5.3 h), the cosmic

ray dose can be estimated as 5.5 lSv/h 9 5.3 h = 29 lSv.

This is only 1.2 % of the worldwide average annual exposure

from natural sources (2.4 mSv) (UNSCEAR 2000). How-

ever, if an individual made 10 round trips between Toronto

and Frankfurt in a year, the annual effective dose due to air

travel could be 0.8 mSv (10 9 2 9 5.5 lSv/h 9 7.2 h =

0.8 mSv), comparable to the public annual dose limit of

1 mSv recommended by the ICRP. For someone who had 40

round trips between Toronto and Hong Kong in a year, such as

the air crew, the annual effective dose could be as high as

6.6 mSv (40 9 2 9 5.5 lSv/h 9 15 h = 6.6 mSv).

It should be mentioned that the result of Canadian popu-

lation exposure to cosmic rays from air travel is an estimate

using air travel statistics in year 2010 and flight information in

2011. Based on the US National Aeronautics and Space

Administration (NASA 2012), solar activity in 2011 was

medium between the solar minimum and maximum. The

estimated population exposure to cosmic rays from air travel

is the value roughly averaged over solar activity. At aircraft

altitude, it is well known that the effective doses can differ up

to tens of percent between solar minimum and solar maxi-

mum,especially fora regionwith lowergeomagnetic rigidity,

such as Canada. The influence of solar activity can be much

more significant for individual flights when assessing indi-

vidual’s effective dose received from a given flight at a given

time. In case of solar particle events, although these events are

rare, the solar events can cause a significant increase in the

effective dose obtained during air traveling.

Conclusions

Based on currently available air travel statistics, the annual

per capita effective dose from air transportation is esti-

mated to be 32 lSv for Canadians, about 10 % of the

average cosmic ray dose received at ground level (310 lSv

per year). While the dose received during air travel will

depend on the number and length of flights, for an average

traveler, the health impact from cosmic radiation exposure

is trivial. For someone who takes many long-haul flights

per year, such as air crew, the annual radiation dose could

approach a few times the dose received from natural

background radiation at ground.

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\30 min 9,300 ± 3700 0.4 ± 0.3

0.5–1 h 24,400 ± 8400 1.4 ± 0.8

1–3 h 31,100 ± 6700 3.5 ± 1.8

[3 h 35,400 ± 2400 5.5 ± 1.2

Table 4 Results of Canadian population dose (effective dose) received from traveling by air together with some travel statistics

Domestic Transborder International Total

Estimated annual departure flights 1,027,475 223,745 54,750 1,305,970

Estimated annual passenger capacity 61,036,395 18,153,275 11,385,810 90,575,480

Canadian air travelers in 2010 22,709,807 6,971,307 8,701,172 38,382,286

Ratio of Canadian passengers to the total passenger capacity 0.372 0.384 0.764

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Annual effective dose per capitaa (lSv) 9.3 4.8 17.5 31.5

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