HomeSearch by dateVacation packagesHotelsFlight dealsCar rentalTravel tips & news
Washington, D.C.

$69+ Cheap flights from Pittsburgh (PIT) to Washington, D.C. (WAS)

This is the cheapest one-way flight price found by a Cheapflights user in the last 72 hours by searching for a flight departing on 1/15. Fares are subject to change and may not be available on all flights or dates of travel.
PIT — WAS
Dec 23 — Dec 301
Mon 12/23
Mon 12/30
1 adult, Economy
We work with more than 300 partners to bring you better travel deals

Find cheap flights from Pittsburgh to Washington, D.C. with Cheapflights

1. Tell us where you want to go
Enter your travel information like dates, passengers, trip type (one-way or round trip), and preferred cabin class then click “Find deals”
2. Select your favorite providers
We find the providers serving your travel needs. Choose up to four travel providers to compare side-by-side for flights, hotels, or car rentals.
3. Compare prices and book
Review each provider’s pricing and select the best option for you! Book through your favorite provider’s website for a seamless experience.

The best prices from Pittsburgh to Washington, D.C. are usually found in August or February, booked 79 days in advance, depart on a Saturday or Tuesday and return on a Friday

Cheap flight deals from Pittsburgh to Washington, D.C.

Discover tips and strategies to find the most affordable flight options for your journey from Pittsburgh (PIT) to Washington, D.C. (WAS). Learn about various techniques such as flexible date searches, comparing prices across and setting up price alerts. Use these methods to find the cheapest flights available for your travel needs. Data last updated December 18, 2024.

Most accurate provider

FlightHub
3 stars

Most trusted provider

FlightHub
3 stars

Round-trip from

$179
(United Airlines)

One-way from

$69
(Southern / Mokulele)

Popular in

September

Cheapest in

August

Average price

$179
Provider with most accurate pricing for Pittsburgh-Washington, D.C. (WAS) flight deals.
Search Deals
Provider most trusted by Cheapflights users for Pittsburgh-Washington, D.C. (WAS) flights.
Search Deals
From Pittsburgh to Washington, D.C. (WAS)
Search Deals
One-way flight from Pittsburgh to Washington, D.C. (WAS)
Search Deals
High demand for flights, 3% potential price rise
Search Deals
Best time to find cheap flights, 2% potential price drop
Search Deals
Average for round-trip flights in December 2024
Search Deals

Find flight deals from Pittsburgh to Washington, D.C.

Cheapest flights from Pittsburgh to Washington, D.C.
Explore the most affordable flight options available from Pittsburgh to Washington, D.C.. Find the lowest fares from popular airlines and budget airlines, with prices last updated on December 18, 2024.

This Mytrip deal was found by Cheapflights users on 12/17. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Mytrip is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Fri 12/2011:59 amPIT - IAD
1 stop4h 11mSouthern / Mokulele
Sat 12/218:25 amIAD - PIT
1 stop6h 08mSouthern / Mokulele
Deal found 12/17$181
This United Airlines deal was found by Cheapflights users on 12/17. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure United Airlines is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 12/2510:35 amPIT - IAD
Nonstop1h 09mUnited Airlines
Sun 12/2910:10 pmIAD - PIT
Nonstop1h 04mUnited Airlines
Deal found 12/17$194
This American Airlines deal was found by Cheapflights users on 12/17. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure American Airlines is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 12/257:42 amPIT - DCA
Nonstop1h 18mAmerican Airlines
Fri 12/277:53 pmDCA - PIT
Nonstop1h 18mAmerican Airlines
Deal found 12/17$194
This Mytrip deal was found by Cheapflights users on 12/17. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Mytrip is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 12/187:33 pmPIT - BWI
2 stops15h 42mSpirit Airlines
Wed 12/257:38 pmBWI - PIT
2 stops23h 55mSpirit Airlines
Deal found 12/17$376
This Mytrip deal was found by Cheapflights users on 12/17. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Mytrip is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Thu 12/1911:59 amPIT - IAD
1 stop4h 11mMultiple Airlines
Sun 12/229:35 pmIAD - PIT
2 stops25h 24mMultiple Airlines
Deal found 12/17$431
This United Airlines deal was found by Cheapflights users on 12/17. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure United Airlines is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 12/257:10 amPIT - BWI
1 stop6h 26mUnited Airlines
Sun 12/296:20 amBWI - PIT
1 stop6h 55mUnited Airlines
Deal found 12/17$486
This Mytrip deal was found by Cheapflights users on 12/16. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Mytrip is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Tue 12/175:32 amPIT - BWI
2 stops17h 51mMultiple Airlines
Thu 12/196:55 amBWI - PIT
2 stops11h 59mMultiple Airlines
Deal found 12/16$494
This Southwest deal was found by Cheapflights users on 12/17. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Southwest is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Sat 12/215:10 pmPIT - BWI
Nonstop1h 05mSouthwest
Tue 12/3111:15 amBWI - PIT
Nonstop1h 05mSouthwest
Deal found 12/17$516
This American Airlines deal was found by Cheapflights users on 12/17. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure American Airlines is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 12/186:30 amPIT - BWI
1 stop6h 25mAmerican Airlines
Wed 12/258:05 amBWI - PIT
1 stop6h 56mAmerican Airlines
Deal found 12/17$533
This Delta deal was found by Cheapflights users on 12/17. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Delta is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Thu 12/196:30 amPIT - BWI
1 stop5h 14mDelta
Sun 1/56:05 amBWI - PIT
1 stop3h 33mDelta
Deal found 12/17$544
This Delta deal was found by Cheapflights users on 12/18. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Delta is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Sun 12/225:52 pmPIT - DCA
1 stop5h 05mDelta
Sat 12/283:00 pmDCA - PIT
2 stops7h 38mDelta
Deal found 12/18$573
This American Airlines deal was found by Cheapflights users on 12/17. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure American Airlines is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 12/256:00 amPIT - IAD
2 stops7h 25mAmerican Airlines
Fri 12/275:00 amIAD - PIT
1 stop4h 01mAmerican Airlines
Deal found 12/17$579

Find flights from Pittsburgh to Washington, D.C. within your budget

Customize your flight search to find flights from Pittsburgh to Washington, D.C. that fit within your specific budget. Explore options based on user searches and filter the results based on your desired price range. Find flights that match your budget for a cost-effective journey. Over the last 7 days, Cheapflights users made 2,558,603 searches. Data last updated December 18, 2024.

Fly from

Any airport

Fly to

Any airport

Route

Depart

Return

Price

PittsburghWashington, D.C.

PIT - IAD

PITIAD

Pittsburgh

Thu 1/16

6:15 am-7:32 am

Nonstop1h 17m

Washington, D.C. Dulles Intl

Sat 1/18

5:55 pm-7:04 pm

Nonstop1h 09m

$179

PittsburghWashington, D.C.

PIT - DCA

PITDCA

Pittsburgh

Thu 1/16

10:21 am-11:41 am

Nonstop1h 20m

Washington, D.C. Reagan-National

Sat 1/18

8:51 am-9:51 am

Nonstop1h 00m

$179

PittsburghBaltimore

PIT - BWI

PITBWI

Pittsburgh

Tue 1/14

11:21 am-3:14 pm

1 stop27h 53m

Baltimore/Washington

Tue 1/21

5:00 pm-10:16 am

1 stop17h 16m

$183

PittsburghWashington, D.C.

PIT - IAD

PITIAD

Pittsburgh

Thu 1/2

7:40 am-11:26 am

1 stop3h 46m

Washington, D.C. Dulles Intl

Mon 1/6

12:55 pm-5:13 pm

1 stop4h 18m

$184

PittsburghWashington, D.C.

PIT - DCA

PITDCA

Pittsburgh

Tue 1/21

7:30 am-12:15 pm

1 stop4h 45m

Washington, D.C. Reagan-National

Thu 1/23

10:45 am-3:04 pm

1 stop4h 19m

$188

PittsburghWashington, D.C.

PIT - DCA

PITDCA

Pittsburgh

Fri 1/17

7:00 am-12:22 pm

1 stop5h 22m

Washington, D.C. Reagan-National

Mon 1/20

4:05 pm-8:34 pm

1 stop4h 29m

$198

PittsburghWashington, D.C.

PIT - DCA

PITDCA

Pittsburgh

Thu 1/23

10:31 am-4:00 pm

2 stops5h 29m

Washington, D.C. Reagan-National

Sun 1/26

6:00 am-9:51 am

1 stop3h 51m

$203

PittsburghBaltimore

PIT - BWI

PITBWI

Pittsburgh

Fri 1/24

12:00 pm-1:05 pm

Nonstop1h 05m

Baltimore/Washington

Fri 1/24

3:35 pm-4:40 pm

Nonstop1h 05m

$259

PittsburghBaltimore

PIT - BWI

PITBWI

Pittsburgh

Fri 1/31

11:21 am-8:50 am

2 stops21h 29m

Baltimore/Washington

Fri 2/7

6:20 am-8:37 pm

2 stops14h 17m

$261

PittsburghBaltimore

PIT - BWI

PITBWI

Pittsburgh

Fri 1/31

8:55 am-1:51 pm

1 stop4h 56m

Baltimore/Washington

Fri 2/7

5:22 pm-11:42 pm

1 stop6h 20m

$282

Flights are sorted by cheapest round-trip flights first.

Deals found on 12/17

Showing 1-10 of 32 results
1
2
3
4

Compare providers for flights from Pittsburgh to Washington, D.C.

Provider information is updated monthly. Please note that these providers often have deals for this flight, but the availability may vary on a day-by-day basis on Cheapflights.
Use the table below to compare price accuracy, trust ratings, and cancellation policies for each provider offering flight deals from Pittsburgh to Washington, D.C. in December.
ProviderPrice AccuracyTrust Score*
ExpediaPrice Accuracy1 starTrust Score*3 stars
eDreamsPrice Accuracy3 starsTrust Score*3 stars
FlightHubPrice Accuracy3 starsTrust Score*3 stars
MytripPrice Accuracy3 starsTrust Score*3 stars
GotogatePrice Accuracy2 starsTrust Score*2 stars

*The Trust Score is based on feedback from users after their booking experience. It measures overall satisfaction, helping us identify issues like hidden fees, problems during the ticketing process, and the quality of customer service. This score is our best indicator of the provider's quality and reliability.

  • Most accurate provider: When it comes to deals on Pittsburgh-Washington, D.C. flights, users find the pricing of FlightHub to be most consistent on Cheapflights vs. FlightHub Users can find the same prices on Pittsburgh-Washington, D.C. flight deals on Cheapflights vs. FlightHub >95% of the time. Price accuracy is based on data collected from Pittsburgh-Washington, D.C. flight searches over the past month and is updated monthly.
  • Most trusted provider: When it comes to deals on Pittsburgh-Washington, D.C. flights, Cheapflights users trust FlightHub the most. FlightHub has received a user feedback score of 3 out of 3 stars (3 being the best), meaning they have been trusted the most by Cheapflights users looking for Pittsburgh-Washington, D.C. flight deals. Provider user feedback score is based on Cheapflights searches over the past month and is updated monthly.

Best time to book a flight from Pittsburgh to Washington, D.C.

Have a flexible travel schedule? Discover the best time to fly to Washington, D.C. from Pittsburgh with our price prediction graph.
Estimated round-trip price
Rates are based on past data. Find the cheapest month and day to book your flight based on your travel requirements, then search for cheap deals.

Travel insights for flights from Pittsburgh to Washington, D.C.

Get recent, data-driven insights about flights from Pittsburgh to Washington, D.C. including ideal travel times, pricing trends, and more.

How far ahead should I book a flight from Pittsburgh to Washington, D.C.?

Use this chart to determine the optimal time to book a round-trip flight from Pittsburgh to Washington, D.C.. Price data was last updated on December 13, 2024.

The best time to book flights from Pittsburgh to Washington, D.C. is 79 days before your desired departure date. The cost of your flight will likely increase significantly if you book two weeks in advance of your flight.

What is the cheapest month to book a flight from Pittsburgh to Washington, D.C.?

Currently, November is the cheapest month in which you can book a flight from Pittsburgh to Washington, D.C. (average of $299). Flying from Pittsburgh to Washington, D.C. in June is currently the most expensive (average of $377). There are several factors that can impact the price of a flight, so comparing airlines, departure airports and flight times can provide users with more options.

What is the cheapest time of day to fly from PIT to WAS?

Find hourly flight availability from Pittsburgh to Washington, D.C.. Discover flight options and departure times throughout the day, allowing you to choose a departure time that suits your schedule. Data last updated December 18, 2024.

Unlike in the afternoon, when flights are generally more expensive, you can save up to 25% on flights from Pittsburgh to Washington, D.C. by exploring options for tickets in the morning.

What is the cheapest day to fly from Pittsburgh to Washington, D.C.?

Use this chart to determine the cheapest time to fly round-trip from Pittsburgh to Washington, D.C.. Price data was last updated on December 16, 2024.

Travelers seeking maximum savings on their Pittsburgh to Washington, D.C. flight should consider departing on Saturday at noon when fares are most often at their lowest. Tuesday afternoons flights should be avoided if possible as fares are typically the most expensive at this time.

Rainfall in Washington, D.C. by month

Plan your trip to Washington, D.C. by taking into account the average rainfall totals by month.

In terms of precipitation, rainfall in Washington, D.C. ranges from 2.6 - 4.0 inches per month. May is typically the wettest month, when rainfall can reach 4.0 in. February is typically the driest time to visit Washington, D.C. when rainfall is around 2.6 in.

Temperature in Washington, D.C. by month

Plan your trip to Washington, D.C. by taking into account the average temperature totals by month.

If weather is an important factor for your trip to Washington, D.C., use this chart to help with planning. For those seeking warmer temperatures, July is the ideal time of year to visit, when temperatures reach an average of 80.6 F. Travelers looking to avoid the cold should look outside of January, when temperatures are typically at their lowest (around 35.6 F).

Reviews of airlines servicing Washington, D.C.

Get insights into the airlines that provide service to Washington, D.C.. Read reviews, discover amenities, and learn about the overall travel experience offered by airlines. Use this information to make informed decisions when choosing an airline for your flight to Washington, D.C.. Reviews last updated December 18, 2024.
Read reviews from past customers who have flown American Airlines, United Airlines and Southern / Mokulele from Pittsburgh to Washington, D.C.. Users can see the overall rating for each airline as well as how each is rated in terms of entertainment options, comfort, food, crew/service, and boarding process.
Southwest
8.1
Very good
4,848 reviews

Crew

8.7

Food

7.2

Entertainment

7.7

Overall

8.1

Boarding

8.2

Comfort

8.1

Reviews

1 / 10

We BARELY made the connection and when we got onboard we were treated like disobedient children who should have arrived earlier because we had to ask other passengers to move so we could sit with our kids. The flight attendants on the first flight were nice but the second one, they were snippy and fairly rude.

Southwest
8.1
Very good
4,848 reviews
Southwest
8.1
Very good
4,848 reviews

Crew

8.7

Food

7.2

Entertainment

7.7

Overall

8.1

Boarding

8.2

Comfort

8.1

Reviews

1 / 10

We BARELY made the connection and when we got onboard we were treated like disobedient children who should have arrived earlier because we had to ask other passengers to move so we could sit with our kids. The flight attendants on the first flight were nice but the second one, they were snippy and fairly rude.

Alaska Airlines
8.0
Very good
9,552 reviews
Southwest
8.1
Very good
4,848 reviews

Crew

8.7

Food

7.2

Entertainment

7.7

Overall

8.1

Boarding

8.2

Comfort

8.1

Reviews

1 / 10

We BARELY made the connection and when we got onboard we were treated like disobedient children who should have arrived earlier because we had to ask other passengers to move so we could sit with our kids. The flight attendants on the first flight were nice but the second one, they were snippy and fairly rude.

Delta
8.0
Very good
8,604 reviews
Southwest
8.1
Very good
4,848 reviews

Crew

8.7

Food

7.2

Entertainment

7.7

Overall

8.1

Boarding

8.2

Comfort

8.1

Reviews

1 / 10

We BARELY made the connection and when we got onboard we were treated like disobedient children who should have arrived earlier because we had to ask other passengers to move so we could sit with our kids. The flight attendants on the first flight were nice but the second one, they were snippy and fairly rude.

Qatar Airways
7.5
Good
3,798 reviews
Southwest
8.1
Very good
4,848 reviews

Crew

8.7

Food

7.2

Entertainment

7.7

Overall

8.1

Boarding

8.2

Comfort

8.1

Reviews

1 / 10

We BARELY made the connection and when we got onboard we were treated like disobedient children who should have arrived earlier because we had to ask other passengers to move so we could sit with our kids. The flight attendants on the first flight were nice but the second one, they were snippy and fairly rude.

JetBlue
7.4
Good
3,279 reviews
Southwest
8.1
Very good
4,848 reviews

Crew

8.7

Food

7.2

Entertainment

7.7

Overall

8.1

Boarding

8.2

Comfort

8.1

Reviews

1 / 10

We BARELY made the connection and when we got onboard we were treated like disobedient children who should have arrived earlier because we had to ask other passengers to move so we could sit with our kids. The flight attendants on the first flight were nice but the second one, they were snippy and fairly rude.

Related info for your journey

Find useful and relevant information for your journey from Pittsburgh to Washington, D.C.. Access travel guides, tips, and recommendations to enhance your travel experience. Get information about local attractions, weather, transportation options, and more.

  • What airport do you fly from for flights from Pittsburgh to Washington, D.C.?

    Pittsburgh (PIT), located 13.5 mi from the city center, is the airport you fly out of when you book flights from Pittsburgh to Washington, D.C.. 6 airlines have flights from Pittsburgh to Washington, D.C. on a regular basis. Booking flights from Pittsburgh to Washington, D.C. should not be difficult; the airport handles an average of 7 outbound flights to Washington, D.C. per day.

  • What are the cheapest airlines flying from Pittsburgh to Washington, D.C. round-trip?

    Cheapflights users have booked flights from Pittsburgh to Washington, D.C. round-trip from $179. Other airlines that can offer you cheap pricing are American Airlines, from $179, and Spirit Airlines, from $183. Users have found that United Airlines is 5% cheaper than the other options available to this destination.

  • What are the cheapest airlines to fly from Pittsburgh to Washington, D.C. one-way?

    $69 is the cheapest one-way deal found within the past few days, from Southern / Mokulele. You may also be able to find cheap deals on Spirit Airlines and JetBlue, with prices starting from $69 and $94, respectively.

  • What are the most popular routes from Pittsburgh to Washington, D.C.?

    The most popular flight routes from Pittsburgh to Washington, D.C. are Pittsburgh - Washington, D.C. Dulles Intl, Pittsburgh - Baltimore/Washington and Pittsburgh - Washington, D.C. Reagan-National.

  • What are the most reliable airlines from Pittsburgh to Washington, D.C.?

    Before booking your flight to Washington, D.C. from Pittsburgh, check out the most reliable airlines to get you to your destination on time: Copa Airlines (94%), Avianca (92%), CommutAir( 92%).

  • What are the cheapest flights from Pittsburgh to Washington, D.C.?

    Looking for the cheapest flight from Pittsburgh to Washington, D.C.? While on average our users pay $1,011, our data indicates the cheapest price to be $122. The most popular route (Pittsburgh - Washington, D.C. Dulles Intl), is priced around $102.

  • Can I find deals for flights from Pittsburgh to Washington, D.C. that include hotel bookings?

    Yes. In addition to deals on Pittsburgh to Washington, D.C. flights, Cheapflights offers vacation packages that include both flights and hotel.

  • How can I find direct flights from Pittsburgh to Washington, D.C.?

    After entering your origin and destination, apply the non-stop filter on the search result page to find direct flights from Pittsburgh to Washington, D.C..

  • Can I find deals for business class flights from Pittsburgh to Washington, D.C.?

    Yes. Cheapflights offers flight deals from Pittsburgh to Washington, D.C. by cabin class. In addition to browsing deals, you can also filter by cabin class on the search results page after making a search.

  • What is the cheapest month to book a flight from Pittsburgh to Washington, D.C.?

    Currently, November is the cheapest month in which you can book a flight from Pittsburgh to Washington, D.C. (average of $299). Flying from Pittsburgh to Washington, D.C. in June is currently the most expensive (average of $377). There are several factors that can impact the price of a flight, so comparing airlines, departure airports and flight times can provide users with more options.

See more FAQs

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.

Alternative routes for Pittsburgh to Washington, D.C.

See prices for flight routes from nearby airports that may be better suited for you.
Newark to Dulles Intl flights
Newark to Reagan-National flights
John F Kennedy Intl to Dulles Intl flights
LaGuardia to Dulles Intl flights
LaGuardia to Reagan-National flights
John F Kennedy Intl to Reagan-National flights
Pittsburgh to Dulles Intl flights
Pittsburgh to Reagan-National flights
Philadelphia to Dulles Intl flights
Philadelphia to Reagan-National flights
Scranton to Reagan-National flights
Scranton to Dulles Intl flights
State College to Dulles Intl flights
Harrisburg to Dulles Intl flights
Allentown to Reagan-National flights
State College to Reagan-National flights
Elmira to Reagan-National flights
Harrisburg to Reagan-National flights
Erie to Dulles Intl flights
Allentown to Dulles Intl flights
Erie to Reagan-National flights

Top 6 airlines flying from Pittsburgh to Washington, D.C.

Discover the top 6 airlines that operate flights from Pittsburgh to Washington, D.C.. Compare their services, reliability, and customer satisfaction ratings to choose the airline that best suits your travel preferences and needs. Over the last 7 days, Cheapflights users made 2,558,603 searches. Data last updated December 18, 2024.
AirlineCheapestAverageFlexibilityOn-time
Spirit AirlinesCheapest$95Average$182FlexibilityNo cancel feeOn-time65%
Southern / MokuleleCheapest$113Average$142FlexibilityNo cancel feeOn-timeN/A
DeltaCheapest$135Average$282FlexibilityNo cancel feeOn-timeN/A
American AirlinesCheapest$151Average$290FlexibilityNo cancel feeOn-time71%
United AirlinesCheapest$158Average$285FlexibilityNo cancel feeOn-time69%
SouthwestCheapest$265Average$380FlexibilityNo cancel feeOn-time63%
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.