Find flights
Deals
When to book
Airlines

Cheap flights from Montreal Pierre Elliott Trudeau Intl Airport to anywhere

Fly from Montreal Pierre Elliott Trudeau Intl Airport to anywhere in the world.

YUL — LHR
16 May — 23 May1
1 adult
Thu 16/5
Thu 23/5

What to know about flights from Pierre Elliott Trudeau Intl

Discover essential information about flights departing from Pierre Elliott Trudeau Intl, including flight schedules, destinations, airlines operating at the Pierre Elliott Trudeau Intl airport, and any specific guidelines or requirements for travellers. Please note that the information is based on the most recent updates available. Data last updated 11 May 2024.

Cheapest airline

American Airlines
On average, American Airlines currently has the cheapest one-way flight from Montreal Pierre Elliott Trudeau Intl.

Cheapest flights from Pierre Elliott Trudeau Intl

Explore the most affordable flight options available from Pierre Elliott Trudeau Intl. Find the lowest fares based on data from user searches, with prices last updated on 11 May 2024. In the last 7 days, Cheapflights users made a total of 868,510 searches.
Fri 31/509:05YUL - YYT
1 stop3h 40mPorter Airlines
Mon 3/618:55YYT - YUL
1 stop4h 08mPorter Airlines
Deal found 9/5£283
Sun 16/617:20YUL - YYT
1 stop5h 55mPorter Airlines
Thu 4/718:35YYT - YUL
1 stop3h 55mPorter Airlines
Deal found 10/5£301
Sun 16/617:20YUL - YYT
1 stop5h 55mPorter Airlines
Thu 4/706:00YYT - YUL
2 stops7h 45mPorter Airlines
Deal found 10/5£304
Fri 31/510:55YUL - YYT
2 stops11h 10mPorter Airlines
Sun 2/607:00YYT - YUL
1 stop4h 28mPorter Airlines
Deal found 10/5£309
Sun 23/610:40YUL - YYT
2 stops12h 35mPorter Airlines
Sun 7/706:00YYT - YUL
2 stops9h 30mPorter Airlines
Deal found 10/5£321
Sat 27/712:30YUL - YYT
2 stops9h 35mPorter Airlines
Sat 7/907:30YYT - YUL
1 stop4h 10mPorter Airlines
Deal found 10/5£327
Wed 10/716:40YUL - YYT
1 stop8h 15mAir Transat
Mon 29/706:55YYT - YUL
1 stop15h 20mAir Transat
Deal found 9/5£331
Fri 5/718:10YUL - YYT
1 stop3h 50mPorter Airlines
Mon 8/714:55YYT - YUL
2 stops9h 25mPorter Airlines
Deal found 10/5£336
Wed 10/716:40YUL - YYT
1 stop8h 15mAir Transat
Tue 30/706:55YYT - YUL
1 stop12h 35mAir Transat
Deal found 9/5£343

Last-minute flight deals from Pierre Elliott Trudeau Intl

Discover last-minute flight deals departing from Pierre Elliott Trudeau Intl. Take advantage of attractive deals offered by airlines for spontaneous travel. These deals are subject to availability and can provide significant savings for flexible travellers. Please note that the availability of last-minute deals can vary and may change quickly. Data last updated 11 May 2024 and based on user searches. In the last 7 days, Cheapflights users made a total of 868,510 searches.
Mon 20/522:05YUL - LGW
Nonstop6h 45mAir Transat
Wed 29/511:35LGW - YUL
Nonstop7h 40mAir Transat
Deal found 10/5£410
Mon 20/510:55YUL - LGW
1 stop18h 50mAir Transat
Wed 29/511:35LGW - YUL
Nonstop7h 40mAir Transat
Deal found 10/5£419
Mon 20/522:05YUL - LGW
Nonstop6h 45mAir Transat
Tue 4/609:40LGW - YUL
1 stop13h 20mAir Transat
Deal found 10/5£429
Mon 20/510:55YUL - LGW
1 stop18h 50mAir Transat
Tue 4/609:40LGW - YUL
1 stop16h 15mAir Transat
Deal found 10/5£435
Sun 19/522:20YUL - LHR
1 stop17h 40mAir Canada
Thu 30/508:40LHR - YUL
1 stop11h 20mAir Canada
Deal found 9/5£450
Mon 20/518:50YUL - LHR
Nonstop6h 40mAir Canada
Tue 4/608:40LHR - YUL
1 stop11h 20mAir Canada
Deal found 10/5£451
Sat 18/522:20YUL - LHR
1 stop17h 40mAir Canada
Tue 28/506:00LHR - YUL
1 stop12h 50mAir Canada
Deal found 10/5£452
Mon 20/522:20YUL - LHR
1 stop17h 40mAir Canada
Wed 29/509:30LHR - YUL
Nonstop7h 05mAir Canada
Deal found 10/5£461
Sat 18/518:50YUL - LHR
Nonstop6h 40mAir Canada
Tue 28/509:30LHR - YUL
Nonstop7h 05mAir Canada
Deal found 10/5£463

Domestic airfare to nearby cities with cheap hotels

Discover domestic flight options from Pierre Elliott Trudeau Intl to cities with affordable hotel accommodations. Plan your travel to both enjoy budget-friendly flights and find affordable lodging in your chosen destination. Please note that the flight options are sourced from user searches. In the last 7 days, Cheapflights users made a total of 868,510 searches and data was last updated 11 May 2024.
Mon 27/513:05YUL - MIA
Nonstop3h 55mAir Transat
Mon 3/618:10MIA - YUL
Nonstop3h 40mAir Transat
Deal found 9/5£143
Mon 27/506:50YUL - FLL
Nonstop3h 35mAir Transat
Mon 3/611:35FLL - YUL
Nonstop3h 25mAir Transat
Deal found 9/5£164
Sat 1/606:50YUL - FLL
Nonstop3h 35mAir Transat
Mon 3/611:35FLL - YUL
Nonstop3h 25mAir Transat
Deal found 10/5£165
Sat 1/606:50YUL - FLL
Nonstop3h 35mAir Transat
Mon 3/611:35FLL - YUL
Nonstop3h 25mAir Transat
Deal found 10/5£166
Mon 20/506:00YUL - MIA
1 stop8h 34mMultiple Airlines
Wed 29/508:00MIA - YUL
Nonstop3h 36mMultiple Airlines
Deal found 10/5£172
Mon 13/511:00YUL - FLL
1 stop8h 34mUnited Airlines
Wed 15/506:00FLL - YUL
1 stop6h 19mUnited Airlines
Deal found 10/5£172
Mon 27/513:05YUL - MIA
Nonstop3h 55mAir Transat
Thu 30/518:10MIA - YUL
Nonstop3h 40mAir Transat
Deal found 9/5£178
Mon 27/513:05YUL - MIA
Nonstop3h 55mAir Transat
Thu 30/518:10MIA - YUL
Nonstop3h 40mAir Transat
Deal found 10/5£179
Thu 13/613:05YUL - FLL
Nonstop3h 35mAir Transat
Mon 17/611:35FLL - YUL
Nonstop3h 25mAir Transat
Deal found 10/5£179

International flights from Pierre Elliott Trudeau Intl

Explore international flight options available from Pierre Elliott Trudeau Intl. Discover the destinations served by airlines operating from Pierre Elliott Trudeau Intl, compare fares, and find the ideal international flight for your travel plans. Please note that the flight options are sourced from user searches, with fares last updated on 11 May 2024. In the last 7 days, Cheapflights users made a total of 868,510 searches.
Fri 24/518:45YUL - ALC
1 stop15h 40mKLM
Sat 1/610:50ALC - YUL
1 stop12h 00mKLM
Deal found 10/5£532
Fri 24/518:45YUL - ALC
1 stop15h 40mKLM
Sat 1/610:50ALC - YUL
2 stops18h 01mKLM
Deal found 10/5£554
Wed 21/818:45YUL - ALC
1 stop15h 40mKLM
Tue 3/911:00ALC - YUL
1 stop11h 50mKLM
Deal found 10/5£607
Wed 21/823:00YUL - ALC
2 stops15h 35mKLM
Tue 3/911:00ALC - YUL
1 stop11h 50mKLM
Deal found 10/5£620
Wed 14/818:45YUL - ALC
1 stop15h 40mKLM
Sat 7/920:50ALC - YUL
2 stops21h 15mKLM
Deal found 10/5£630
Wed 14/818:45YUL - ALC
1 stop19h 50mKLM
Sat 7/922:50ALC - YUL
1 stop24h 00mKLM
Deal found 10/5£649
Fri 24/519:00YUL - ALC
2 stops15h 25mKLM
Sat 1/610:50ALC - YUL
2 stops18h 01mKLM
Deal found 10/5£652
Wed 21/823:00YUL - ALC
2 stops15h 35mKLM
Tue 3/921:35ALC - YUL
2 stops23h 25mKLM
Deal found 10/5£683
Thu 22/823:45YUL - ALC
1 stop28h 20mMultiple Airlines
Mon 2/920:40ALC - YUL
1 stop26h 45mMultiple Airlines
Deal found 10/5£702

Direct flights from Pierre Elliott Trudeau Intl

Discover airlines that offer direct flights from Pierre Elliott Trudeau Intl to various destinations. Avoid layovers and travel efficiently with direct flight options, saving you time and providing a more convenient travel experience. Please note that the direct flight options are based on data from 11 May 2024 and based on user searches. In the last 7 days, Cheapflights users made a total of 868,510 searches.
Mon 20/522:05YUL - LGW
Nonstop6h 45mAir Transat
Wed 29/511:35LGW - YUL
Nonstop7h 40mAir Transat
Deal found 10/5£410
Tue 21/522:05YUL - LGW
Nonstop6h 45mAir Transat
Tue 28/511:35LGW - YUL
Nonstop7h 40mAir Transat
Deal found 9/5£412
Sat 25/522:05YUL - LGW
Nonstop6h 45mAir Transat
Wed 29/511:35LGW - YUL
Nonstop7h 40mAir Transat
Deal found 10/5£414
Tue 17/922:05YUL - LGW
Nonstop6h 45mAir Transat
Fri 4/1011:35LGW - YUL
Nonstop7h 40mAir Transat
Deal found 10/5£414
Tue 21/522:05YUL - LGW
Nonstop6h 45mAir Transat
Mon 3/611:40LGW - YUL
Nonstop7h 35mAir Transat
Deal found 10/5£416
Tue 21/522:05YUL - LGW
Nonstop6h 45mAir Transat
Tue 28/511:35LGW - YUL
Nonstop7h 40mAir Transat
Deal found 9/5£417
Sun 9/622:05YUL - LGW
Nonstop6h 45mAir Transat
Tue 10/911:35LGW - YUL
Nonstop7h 40mAir Transat
Deal found 9/5£420
Tue 21/522:05YUL - LGW
Nonstop6h 45mAir Transat
Tue 28/511:35LGW - YUL
Nonstop7h 40mAir Transat
Deal found 9/5£423
Sat 28/922:05YUL - LGW
Nonstop6h 45mAir Transat
Wed 16/1011:35LGW - YUL
Nonstop7h 40mAir Transat
Deal found 10/5£425

Find flights from Pierre Elliott Trudeau Intl within your budget

MISSING STRING [DIRECT_FLIGHTS_ORIGIN_BUDGET_RANGE_FINDER_SUBTITLE_UPDATED]

Fly to

Any airport

Budget

£283 - £343

Route

Depart

Return

Price

Montreal Pierre Elliott Trudeau IntlSt John's

YUL - YYT

YULYYT

Montreal Pierre Elliott Trudeau Intl

Fri 31/5

1 stop3h 40m

St John's

Mon 3/6

1 stop4h 08m

£283

Montreal Pierre Elliott Trudeau IntlSt John's

YUL - YYT

YULYYT

Montreal Pierre Elliott Trudeau Intl

Sun 16/6

1 stop5h 55m

St John's

Thu 4/7

1 stop3h 55m

£301

Montreal Pierre Elliott Trudeau IntlSt John's

YUL - YYT

YULYYT

Montreal Pierre Elliott Trudeau Intl

Sun 16/6

1 stop5h 55m

St John's

Thu 4/7

2 stops7h 45m

£304

Montreal Pierre Elliott Trudeau IntlSt John's

YUL - YYT

YULYYT

Montreal Pierre Elliott Trudeau Intl

Fri 31/5

2 stops11h 10m

St John's

Sun 2/6

1 stop4h 28m

£309

Montreal Pierre Elliott Trudeau IntlSt John's

YUL - YYT

YULYYT

Montreal Pierre Elliott Trudeau Intl

Sun 23/6

2 stops12h 35m

St John's

Sun 7/7

2 stops9h 30m

£321

Montreal Pierre Elliott Trudeau IntlSt John's

YUL - YYT

YULYYT

Montreal Pierre Elliott Trudeau Intl

Sat 27/7

2 stops9h 35m

St John's

Sat 7/9

1 stop4h 10m

£327

Montreal Pierre Elliott Trudeau IntlSt John's

YUL - YYT

YULYYT

Montreal Pierre Elliott Trudeau Intl

Wed 10/7

1 stop8h 15m

St John's

Mon 29/7

1 stop15h 20m

£331

Montreal Pierre Elliott Trudeau IntlSt John's

YUL - YYT

YULYYT

Montreal Pierre Elliott Trudeau Intl

Fri 5/7

1 stop3h 50m

St John's

Mon 8/7

2 stops9h 25m

£336

Montreal Pierre Elliott Trudeau IntlSt John's

YUL - YYT

YULYYT

Montreal Pierre Elliott Trudeau Intl

Wed 10/7

1 stop8h 15m

St John's

Tue 30/7

1 stop12h 35m

£343

Flights are sorted by cheapest first

Deals found on 9/5

When is the best time to book a flight from Montreal Pierre Elliott Trudeau Intl Airport?

Use this chart to determine the optimal time to book a return flight from Pierre Elliott Trudeau Intl. Price data was last updated on 3 May 2024.
Booking 8 days in advance of your planned departure date is, on average, the best time to get cheap flights from Montreal Pierre Elliott Trudeau Intl Airport. The general trend is that the closer you book to the departure date, the more expensive your flight will be.
Search Deals

When is the cheapest time to fly from Montreal Pierre Elliott Trudeau Intl Airport?

Use this chart to determine the cheapest time to fly return from Pierre Elliott Trudeau Intl. Price data was last updated on 5 May 2024.
Morning
Midday
Afternoon
Evening
All times are departure.
Those who are seeking the cheapest fare on flights departing from Montreal Pierre Elliott Trudeau Intl Airport would be wise to consider leaving during Monday evenings when prices are typically at their lowest. When considering other options, price-conscious travelers should avoid Thursday evenings when fares are usually the most expensive.
Search Deals

Average price of flights from Pierre Elliott Trudeau Intl by month

Plan your trip from Pierre Elliott Trudeau Intl by taking into account the cheapest months to travel. The average price of a one-way flight from Pierre Elliott Trudeau Intl is currently £197 while a return flight costs £317. Price data was last updated on 5 May 2024.

Currently, February is the cheapest month in which you can book a flight from Montreal Pierre Elliott Trudeau Intl Airport (average of £464). Flying from Montreal Pierre Elliott Trudeau Intl Airport in July will prove the most costly (average of £726). There are multiple factors that influence the price of a flight so comparing airlines, departure airports and times can help keep costs down.

January

£89

February

£99

March

£95

April

£105

May

£105

June

£132

July

£136

August

£117

September

£111

October

£127

November

£92

December

£97

Airline reviews for flights from Pierre Elliott Trudeau Intl

Get insights into the airlines that provide service from Pierre Elliott Trudeau Intl. Read reviews, discover amenities, and learn about the overall travel experience offered by airlines. Use this information to make informed decisions when choosing airline for your flight from Pierre Elliott Trudeau Intl. In the last 7 days, Cheapflights users made a total of 868,510 searches.
8.1
Very Good
10,751 reviews

Comfort

7.9

Food

7.4

Entertainment

8.0

Crew

8.6

Overall

8.1

Boarding

8.2

Reviews

1 / 10

Four hour delay (missing two screws). Seats in need of repair.

8.1
Very Good
10,751 reviews
8.1
Very Good
10,751 reviews

Comfort

7.9

Food

7.4

Entertainment

8.0

Crew

8.6

Overall

8.1

Boarding

8.2

Reviews

1 / 10

Four hour delay (missing two screws). Seats in need of repair.

7.9
Good
1,589 reviews
8.1
Very Good
10,751 reviews

Comfort

7.9

Food

7.4

Entertainment

8.0

Crew

8.6

Overall

8.1

Boarding

8.2

Reviews

1 / 10

Four hour delay (missing two screws). Seats in need of repair.

7.8
Good
2,003 reviews
8.1
Very Good
10,751 reviews

Comfort

7.9

Food

7.4

Entertainment

8.0

Crew

8.6

Overall

8.1

Boarding

8.2

Reviews

1 / 10

Four hour delay (missing two screws). Seats in need of repair.

7.8
Good
1,377 reviews
8.1
Very Good
10,751 reviews

Comfort

7.9

Food

7.4

Entertainment

8.0

Crew

8.6

Overall

8.1

Boarding

8.2

Reviews

1 / 10

Four hour delay (missing two screws). Seats in need of repair.

7.7
Good
1,060 reviews
8.1
Very Good
10,751 reviews

Comfort

7.9

Food

7.4

Entertainment

8.0

Crew

8.6

Overall

8.1

Boarding

8.2

Reviews

1 / 10

Four hour delay (missing two screws). Seats in need of repair.

Browse thousands of different options on Cheapflights for your next trip

Toggle through the tabs below to find thousands of options on Cheapflights for your next trip.

Fly from other Canada cities
Consider departing from one of these cities also located in Canada. Flight origins are based on user searches made on Cheapflights and were last updated on 11 May 2024.

Related info for your journey

Access useful and relevant information related to your journey from Pierre Elliott Trudeau Intl. This can include details such as airport transportation, visa requirements, travel insurance, luggage regulations, and any other information that can ensure a smooth and hassle-free travel experience. Please note that the information is based on general guidance and may need to be verified with official sources. Data last updated 11 May 2024.
  • What are the most popular destinations to fly to from Montreal Pierre Elliott Trudeau Intl Airport?

    This month, the top selected destinations from Montreal Pierre Elliott Trudeau Intl Airport are Paris Charles de Gaulle Airport, Athens, Algiers. Throughout the year, Paris Charles de Gaulle Airport, Algiers, Athens are some of the top choices made by users flying from Montreal Pierre Elliott Trudeau Intl Airport.

  • What is the cheapest flight from Montreal Pierre Elliott Trudeau Intl Airport to anywhere?

    Users have flown out of Montreal Pierre Elliott Trudeau Intl Airport for as low as £96 to Halifax (prices may vary depending on the airline and departure time). On average, users have booked flights for £516 to fly from Montreal Pierre Elliott Trudeau Intl Airport.

  • What are the cheapest airlines flying from Montreal Pierre Elliott Trudeau Intl Airport to anywhere?

    Over the past few days, we've found that Lynx Air, WestJet, and Air Canada have the cheapest prices from Montreal Pierre Elliott Trudeau Intl Airport. Lynx Air flights from Montreal Pierre Elliott Trudeau Intl Airport to Las Vegas Harry Reid Intl (£50), WestJet flights from Montreal Pierre Elliott Trudeau Intl Airport to Calgary (£71), and Air Canada flights from Montreal Pierre Elliott Trudeau Intl Airport to Beirut (£106).

  • What is the farthest nonstop flight from Montreal Pierre Elliott Trudeau Intl Airport?

    Travelers looking to get as far as possible can consider Seoul, New Delhi, and Tokyo as potential destinations for their travel.

  • What are popular destinations to fly to from Montreal Pierre Elliott Trudeau Intl Airport?

    If you’re flying from Montreal Pierre Elliott Trudeau Intl Airport, these routes are more frequently taken by airlines Toronto (886 flights per day), New York (717 flights per day) and Paris (312 flights per day).

  • Where are the cheapest places to fly to from Montreal Pierre Elliott Trudeau Intl Airport?

    Check out the cheapest flights from Montreal Pierre Elliott Trudeau Intl Airport to embark to:
    Travel from Montreal to London from £346 round trip

  • Which airlines fly from Montreal Pierre Elliott Trudeau Intl Airport?

    Many airlines operate round-trip flights from Montreal Pierre Elliott Trudeau Intl Airport: Lynx Air, Flair Airlines, Air Canada, Porter Airlines, WestJet. These airlines fly to the following popular destinations: Calgary, Vancouver, Beirut, Washington, D.C., Las Vegas.

  • What is the cheapest premium economy flight from Montreal Pierre Elliott Trudeau Intl Airport?

    Here are some of the cheapest offers we have found for the cheapest premium economy flights from Montreal Pierre Elliott Trudeau Intl Airport.
    Montreal Pierre Elliott Trudeau Intl to Toronto Pearson Intl Airport from £467
    Montreal Pierre Elliott Trudeau Intl to London Gatwick Airport from £1,106
    Montreal Pierre Elliott Trudeau Intl to Paris Charles de Gaulle Airport from £1,240
    Montreal Pierre Elliott Trudeau Intl to Philadelphia from £1,301

  • What is the cheapest month to fly from Montreal Pierre Elliott Trudeau Intl Airport?

    At the present moment the cheapest month to fly from Montreal Pierre Elliott Trudeau Intl Airport is currently February; with July being the most expensive. Prices will vary depending on multiple factors such as booking in advance, airline and departure airports and times.

  • When is the cheapest time to fly from Montreal Pierre Elliott Trudeau Intl Airport?

    Those who are seeking the cheapest fare on flights departing from Montreal Pierre Elliott Trudeau Intl Airport would be wise to consider leaving during Monday evenings when prices are typically at their lowest. When considering other options, price-conscious travelers should avoid Thursday evenings when fares are usually the most expensive.

  • When is the best time to book a flight from Montreal Pierre Elliott Trudeau Intl Airport?

    Booking 8 days in advance of your planned departure date is, on average, the best time to get cheap flights from Montreal Pierre Elliott Trudeau Intl Airport. The general trend is that the closer you book to the departure date, the more expensive your flight will be.

  • How does Cheapflights help users find flights from Pierre Elliott Trudeau Intl?

    Cheapflights makes it easy to find flights from Pierre Elliott Trudeau Intl by helping our users search from 900+ travel sites for deals. We also provide you with filters for cabin, price, airline, airports, number of stops, and many more to narrow down that perfect flight.

  • Why should you use Cheapflights to find cheap flight tickets from Pierre Elliott Trudeau Intl?

    Cheapflights simply makes it quick and affordable to book flights from Pierre Elliott Trudeau Intl by bringing together all flight options from hundreds of airlines and agencies online — and we put them in one place for you to choose from. Plus, Cheapflights is 100% free to use for all.

  • Can Cheapflights find flights from Pierre Elliott Trudeau Intl with no change fees?

    Need flexible booking options for your flight from Pierre Elliott Trudeau Intl ? Don’t worry, Cheapflights have you covered. Use our search filter to only show flights with no change fees.

  • Can Cheapflights notify me if prices for flights from Pierre Elliott Trudeau Intl become cheaper?

    Yes, Cheapflights has a feature called Price Alerts, which offers users the ability to be notified when flight prices change. Track prices for your flight from Pierre Elliott Trudeau Intl today and book when you’re ready!

See more FAQs

Fly with Cheapflights

Find the best flight deals on Cheapflights, where travellers can enjoy low prices and a wide availability of flights to their desired destinations.

How does Cheapflights help users find flights from Pierre Elliott Trudeau Intl?

Cheapflights makes it easy to find flights from Pierre Elliott Trudeau Intl by helping our users search from 900+ travel sites for deals. We also provide you with filters for cabin, price, airline, airports, number of stops, and many more to narrow down that perfect flight.

Why should you use Cheapflights to find cheap flight tickets from Pierre Elliott Trudeau Intl?

Cheapflights simply makes it quick and affordable to book flights from Pierre Elliott Trudeau Intl by bringing together all flight options from hundreds of airlines and agencies online — and we put them in one place for you to choose from. Plus, Cheapflights is 100% free to use for all.

Can Cheapflights find flights from Pierre Elliott Trudeau Intl with no change fees?

Need flexible booking options for your flight from Pierre Elliott Trudeau Intl ? Don’t worry, Cheapflights have you covered. Use our search filter to only show flights with no change fees.

Can Cheapflights notify me if prices for flights from Pierre Elliott Trudeau Intl become cheaper?

Yes, Cheapflights has a feature called Price Alerts, which offers users the ability to be notified when flight prices change. Track prices for your flight from Pierre Elliott Trudeau Intl today and book when you’re ready!

100% Free
Cheapflights is completely free to use, so you can start saving the moment you arrive.
Book with Flexibility
Our users can plan ahead with confidence and find flights with no change fees
Travel Smart
Millions of people come to us for their flight needs every year. We help make travel planning easy by providing useful insights and data-driven graphs that can inform your decisions.