HomeSearch by dateVacation packagesHotelsFlight dealsCar rentalTravel tips & news
Seattle

$89+ Cheap flights from San Diego to Seattle (SAN - SEA)

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 4/22. Fares are subject to change and may not be available on all flights or dates of travel.
SAN — SEA
mar 26 — abr 21
qua 3/26
qua 4/2
1 adult, Economy
We work with more than 300 partners to bring you better travel deals

Find cheap flights from San Diego to Seattle 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.

Cheapflights Tip: The best prices from San Diego to Seattle/Tacoma Intl are usually found in January or October, booked 34 days in advance, depart on a Friday or Thursday and return on a Wednesday

Cheap flight deals from San Diego to Seattle

Discover tips and strategies to find the most affordable flight options for your journey from San Diego (SAN) to Seattle (SEA). 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 março 21, 2025.

Most accurate provider

FlightHub
3 stars

Most trusted provider

FlightHub
3 stars

Round-trip from

$140
(Cheapflightsfares)

One-way from

$89
(Delta)

Popular in

July

Cheapest in

January

Average price

$287

Good round-trip deal

$255 or less

Good one-way deal

$131 or less
Provider with most accurate pricing for San Diego-Seattle/Tacoma Intl flight deals.
Search Deals
Provider most trusted by Cheapflights users for San Diego-Seattle/Tacoma Intl flights.
Search Deals
From San Diego to Seattle/Tacoma Intl
Search Deals
One-way flight from San Diego to Seattle/Tacoma Intl
Search Deals
Highest demand for flights based on searches. 15% potential increase in price ($42 potential increase over avg. RT price).
Search Deals
Cheapest flight prices on average. 2% potential price decrease ($6 potential savings vs. average RT price).
Search Deals
Average for round-trip flights in March 2025
Search Deals
Price to beat on a round-trip flight from San Diego to Seattle/Tacoma Intl.
Search Deals
Price to beat on a one-way flight from San Diego to Seattle/Tacoma Intl.
Search Deals

Find flight deals from San Diego to Seattle

Cheapest flights from San Diego to Seattle
Explore the most affordable flight options available from San Diego to Seattle. Find the lowest fares from popular airlines and budget airlines, with prices last updated on março 21, 2025.

This Cheapflightsfares deal was found by Cheapflights users on 3/19. 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 Cheapflightsfares is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
sáb 5/106:15 amSAN - SEA
1 stop8h 10mSpirit Airlines
seg 5/193:20 pmSEA - SAN
1 stop8h 33mSpirit Airlines
Deal found 3/19$140
This Expedia deal was found by Cheapflights users on 3/20. 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 Expedia is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
qui 5/17:55 pmSAN - SEA
Nonstop3h 04mMultiple Airlines
dom 5/48:56 pmSEA - SAN
1 stop10h 38mMultiple Airlines
Deal found 3/20$152
This Delta deal was found by Cheapflights users on 3/20. 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.
qua 4/167:20 amSAN - SEA
Nonstop3h 12mDelta
qua 4/237:35 pmSEA - SAN
Nonstop2h 45mDelta
Deal found 3/20$177
This Alaska Airlines deal was found by Cheapflights users on 3/20. 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 Alaska Airlines is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
qua 4/96:15 amSAN - SEA
1 stop5h 19mAlaska Airlines
seg 4/149:15 pmSEA - SAN
Nonstop2h 44mAlaska Airlines
Deal found 3/20$190
This Hawaiian Airlines deal was found by Cheapflights users on 3/21. 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 Hawaiian Airlines is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
sáb 5/1712:45 pmSAN - SEA
1 stop6h 25mHawaiian Airlines
dom 5/254:16 pmSEA - SAN
Nonstop2h 45mHawaiian Airlines
Deal found 3/21$213
This United Airlines deal was found by Cheapflights users on 3/20. 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.
sáb 4/1910:16 amSAN - SEA
2 stops8h 15mUnited Airlines
sáb 4/267:33 pmSEA - SAN
1 stop4h 45mUnited Airlines
Deal found 3/20$228
This American Airlines deal was found by Cheapflights users on 3/20. 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.
ter 6/310:00 amSAN - SEA
1 stop7h 05mAmerican Airlines
ter 7/16:30 amSEA - SAN
1 stop5h 25mAmerican Airlines
Deal found 3/20$229
This Frontier deal was found by Cheapflights users on 3/20. 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 Frontier is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
sáb 3/299:46 pmSAN - SEA
1 stop11h 44mFrontier
seg 4/711:36 amSEA - SAN
1 stop8h 53mFrontier
Deal found 3/20$278

Cheapflights Fare Finder

Customize your flight search to find flights from San Diego to Seattle 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 março 21, 2025.
Use the filters below to find and compare flights from San Diego to Seattle that are best for you.

Fly from

San Diego

Fly to

Seattle

Route

Depart

Return

Price

San DiegoSeattle

SAN - SEA

SANSEA

San Diego

sáb 5/10

6:15 am-2:25 pm

1 stop8h 10m

Seattle/Tacoma Intl

seg 5/19

3:20 pm-11:53 pm

1 stop8h 33m

$140

San DiegoSeattle

SAN - SEA

SANSEA

San Diego

qui 5/1

7:55 pm-10:59 pm

Nonstop3h 04m

Seattle/Tacoma Intl

dom 5/4

8:56 pm-7:34 am

1 stop10h 38m

$152

San DiegoSeattle

SAN - SEA

SANSEA

San Diego

qua 4/16

7:20 am-10:32 am

Nonstop3h 12m

Seattle/Tacoma Intl

qua 4/23

7:35 pm-10:20 pm

Nonstop2h 45m

$177

San DiegoSeattle

SAN - SEA

SANSEA

San Diego

qua 4/9

6:15 am-11:34 am

1 stop5h 19m

Seattle/Tacoma Intl

seg 4/14

9:15 pm-11:59 pm

Nonstop2h 44m

$190

San DiegoSeattle

SAN - SEA

SANSEA

San Diego

sáb 5/17

12:45 pm-7:10 pm

1 stop6h 25m

Seattle/Tacoma Intl

dom 5/25

4:16 pm-7:01 pm

Nonstop2h 45m

$213

San DiegoSeattle

SAN - SEA

SANSEA

San Diego

sáb 4/19

10:16 am-6:31 pm

2 stops8h 15m

Seattle/Tacoma Intl

sáb 4/26

7:33 pm-12:18 am

1 stop4h 45m

$228

San DiegoSeattle

SAN - SEA

SANSEA

San Diego

ter 6/3

10:00 am-5:05 pm

1 stop7h 05m

Seattle/Tacoma Intl

ter 7/1

6:30 am-11:55 am

1 stop5h 25m

$229

San DiegoSeattle

SAN - SEA

SANSEA

San Diego

seg 3/31

9:19 pm-9:35 am

1 stop12h 16m

Seattle/Tacoma Intl

sáb 4/5

7:51 pm-7:39 am

1 stop11h 48m

$278

San DiegoSeattle

SAN - SEA

SANSEA

San Diego

sex 6/13

7:55 pm-1:25 am

1 stop5h 30m

Seattle/Tacoma Intl

sáb 6/14

5:30 am-1:00 pm

2 stops7h 30m

$313

San DiegoSeattle

SAN - SEA

SANSEA

San Diego

ter 4/22

10:25 am-1:30 pm

Nonstop3h 05m

$89

Flights are sorted by cheapest round-trip flights first.

Deals found on 3/20

Showing 1-10 of 17 results
1
2

Compare providers for flights from San Diego to Seattle

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 San Diego to Seattle in March.
ProviderPrice AccuracyTrust Score*
ExpediaPrice Accuracy1 starTrust Score*3 stars
FlightHubPrice Accuracy3 starsTrust Score*3 stars
eDreamsPrice Accuracy3 starsTrust Score*3 stars
PricelinePrice Accuracy1 starTrust Score*3 stars
CheapflightsfaresPrice Accuracy3 starsTrust Score*2 stars
CheapTicketsDealPrice Accuracy3 starsTrust Score*3 stars
Kiwi.comPrice Accuracy3 starsTrust Score*2 stars
CheapfaremartPrice Accuracy-Trust Score*3 stars
Trip.comPrice Accuracy1 starTrust Score*3 stars
Justfly.comPrice Accuracy3 starsTrust Score*3 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 San Diego-Seattle flights, users find the pricing of FlightHub to be most consistent on Cheapflights vs. FlightHub Users can find the same prices on San Diego-Seattle flight deals on Cheapflights vs. FlightHub >95% of the time. Price accuracy is based on data collected from San Diego-Seattle flight searches over the past month and is updated monthly.
  • Most trusted provider: When it comes to deals on San Diego-Seattle 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 San Diego-Seattle flight deals. Provider user feedback score is based on Cheapflights searches over the past month and is updated monthly.

The best insider tips for San Diego to Seattle flights

Snippets provided in this section are AI-generated based on a summarization of Cheapflights-commissioned articles. The articles are presented as-is, for general informational purposes only, and may not be up-to-date. The opinions contained in the articles are original to the author and reflect their authentic experience, which may vary significantly from the experience of others.
Cheapflights partnered with top experts to bring you the best recommendations for your San Diego to Seattle trip
Airports
SAN

Plan to arrive at least two hours before your flight due to potential traffic congestion near SAN.

Read more about SANby Blane Bachelor
SEA

Use the Link light rail from SEA to downtown Seattle for a cost-effective, 40-minute journey.

Read more about SEAby Brandon Schultz
Our travel experts
Blane Bachelor

Blane Bachelor

Expert on SAN

Blane Bachelor

Blane Bachelor

Blane Bachelor is a journalist and editor specializing in travel and aviation who writes regularly for top global outlets. Born and raised in Florida, Blane has worked and lived in four countries, including the Netherlands, where she’s currently based with her family. Her favorite way to get to know a new destination is by running or riding a bike around town – or hearing a spooky ghost story about local history. She will always choose the window seat.

Read more
Brandon Schultz

Brandon Schultz

Expert on SEA

Brandon Schultz

Brandon Schultz

Brandon Schultz is an award-winning food and travel writer based in New York City. His work has appeared in Forbes, AAA, Thrillist, Travel + Leisure, and The Daily Meal, among many others, and he is the author of 6 books, including 3 cookbooks.

Read more

Best time to book a flight from San Diego to Seattle

Have a flexible travel schedule? Discover the best time to fly to Seattle from San Diego 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.

Cheapflights Insights

Everything you need to know about your flight from San Diego to Seattle

How far ahead should I book a flight from San Diego to Seattle?

Use this chart to determine the optimal time to book a round-trip flight from San Diego to Seattle. Price data was last updated on March 14, 2025.

The price you pay for your flight from San Diego to Seattle may vary depending on when you book. For the best chance of a lower fare, look to book 34 days in advance of your trip. Fares are likely to increase a fortnight or so before your departure date.

What is the cheapest month to book a flight from San Diego to Seattle?

Currently, January is the cheapest month in which you can book a flight from San Diego to Seattle (average of $238). Flying from San Diego to Seattle in July is currently the most expensive (average of $411). 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 SAN to SEA?

Find hourly flight availability from San Diego to Seattle. Discover flight options and departure times throughout the day, allowing you to choose a departure time that suits your schedule. Data last updated março 21, 2025.

It’s typically best to fly out from San Diego to Seattle in the evening. Doing so could potentially save you 29% on the flight price compared to flying in the morning, which is usually more expensive.

What is the cheapest day to fly from San Diego to Seattle?

Use this chart to determine the cheapest time to fly round-trip from San Diego to Seattle. Price data was last updated on March 16, 2025.

Travelers seeking maximum savings on their San Diego to Seattle flight should consider departing on Thursday afternoons when fares are most often at their lowest. Sunday at noon flights should be avoided if possible as fares are typically the most expensive at this time.

Weekly flight availability from San Diego to Seattle

Explore weekly flight availability from San Diego to Seattle. Discover flights operating on different days of the week, giving you the flexibility to choose a travel day that best fits your plans. Compare info to find the most convenient option for your journey. Data last updated março 21, 2025.

The most flights from SAN to SEA are scheduled on a Friday (61 on average). You will have fewer flight options on Saturday, which is when the least amount of flights are scheduled (25 on average).

Rainfall in Seattle by month

Plan your trip to Seattle by taking into account the average rainfall totals by month.

In terms of precipitation, rainfall in Seattle ranges from 0.7 - 6.6 inches per month. November is typically the wettest month, when rainfall can reach 6.6 in. July is typically the driest time to visit Seattle when rainfall is around 0.7 in.

Temperature in Seattle by month

Plan your trip to Seattle by taking into account the average temperature totals by month.

If weather is an important factor for your trip to Seattle, 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 66.2 F. Travelers looking to avoid the cold should look outside of December, when temperatures are typically at their lowest (around 41.0 F).

Reviews of airlines servicing Seattle

Get insights into the airlines that provide service to Seattle. 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 Seattle. Reviews last updated março 21, 2025.
Read through reviews of airlines operating flights from San Diego to Seattle, such as Southwest, Alaska Airlines and Delta. Reviews also offer insight into each airline's entertainment options, comfort, food, crew/service, and boarding process.
Southwest
8.1
Very good
4,278 reviews

Overall

8.1

Entertainment

7.6

Comfort

8.1

Crew

8.7

Boarding

8.2

Food

7.1

Reviews

1 / 20
10.0
Excellent

Merlyn,Feb 2025

LAX - SMF

New Terminal is neat, lost of stores and places to catch a bite.
Southwest
8.1
Very good
4,278 reviews
Southwest
8.1
Very good
4,278 reviews

Overall

8.1

Entertainment

7.6

Comfort

8.1

Crew

8.7

Boarding

8.2

Food

7.1

Reviews

1 / 20
10.0
Excellent

Merlyn,Feb 2025

LAX - SMF

New Terminal is neat, lost of stores and places to catch a bite.
Alaska Airlines
8.0
Very good
9,759 reviews
Southwest
8.1
Very good
4,278 reviews

Overall

8.1

Entertainment

7.6

Comfort

8.1

Crew

8.7

Boarding

8.2

Food

7.1

Reviews

1 / 20
10.0
Excellent

Merlyn,Feb 2025

LAX - SMF

New Terminal is neat, lost of stores and places to catch a bite.
Delta
8.0
Very good
7,895 reviews
Southwest
8.1
Very good
4,278 reviews

Overall

8.1

Entertainment

7.6

Comfort

8.1

Crew

8.7

Boarding

8.2

Food

7.1

Reviews

1 / 20
10.0
Excellent

Merlyn,Feb 2025

LAX - SMF

New Terminal is neat, lost of stores and places to catch a bite.
Hawaiian Airlines
7.9
Good
2,325 reviews
Southwest
8.1
Very good
4,278 reviews

Overall

8.1

Entertainment

7.6

Comfort

8.1

Crew

8.7

Boarding

8.2

Food

7.1

Reviews

1 / 20
10.0
Excellent

Merlyn,Feb 2025

LAX - SMF

New Terminal is neat, lost of stores and places to catch a bite.
United Airlines
7.4
Good
8,605 reviews
Southwest
8.1
Very good
4,278 reviews

Overall

8.1

Entertainment

7.6

Comfort

8.1

Crew

8.7

Boarding

8.2

Food

7.1

Reviews

1 / 20
10.0
Excellent

Merlyn,Feb 2025

LAX - SMF

New Terminal is neat, lost of stores and places to catch a bite.

Related info for your journey

Find useful and relevant information for your journey from San Diego to Seattle. Access travel guides, tips, and recommendations to enhance your travel experience. Get information about local attractions, weather, transportation options, and more.

  • What airports do I use to fly from San Diego to Seattle?

    If you book a flight from San Diego to Seattle, you will be flying from San Diego to Seattle/Tacoma Intl. Flights to Seattle/Tacoma Intl (SEA) from San Diego (SAN) take 2h 56m for a nonstop flight. There are 41 flights from San Diego to Seattle per day from 8 airlines.

  • How popular is this San Diego to Seattle flight route?

    Within the past month, 113 users have taken a look at flights from San Diego to Seattle/Tacoma Intl.

  • What are the cheapest airlines flying from San Diego to Seattle round-trip?

    Flying on Spirit Airlines is currently your cheapest option to Seattle, with prices starting at $140. Additional round-trip tickets that might be worth considering are offered by Delta and Alaska Airlines, with the lowest prices starting at $177 and $190, respectively. Spirit Airlines is priced at 40% lower than the current average price of a flight leaving 3 months from now.

  • What are the cheapest airlines to fly from San Diego to Seattle one-way?

    For one-way options, check prices for Delta. According to our data, you can fly for as low as $89. Users have also found prices from $90 and $91 on Spirit Airlines and Alaska Airlines, respectively.

  • What are the most reliable airlines from San Diego to Seattle?

    Consider SkyWest Airlines (100%), Aeromexico (100%) or ITA Airways (100%) when booking your flight. These represent the most reliable airlines when flying from San Diego to Seattle.

  • What are the cheapest flights from San Diego to Seattle?

    While on average a flight from San Diego to Seattle is generally $1,180, our data shows the cheapest flight currently is $88. When looking at the most popular route, (San Diego - Seattle/Tacoma Intl), you can expect to pay $100 for that flight.

  • Can I find deals for flights from San Diego to Seattle that include hotel bookings?

    Yes. In addition to deals on San Diego to Seattle flights, Cheapflights offers vacation packages that include both flights and hotel.

  • How can I find direct flights from San Diego to Seattle?

    After entering your origin and destination, apply the non-stop filter on the search result page to find direct flights from San Diego to Seattle.

  • Can I find deals for business class flights from San Diego to Seattle?

    Yes. Cheapflights offers flight deals from San Diego to Seattle 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 San Diego to Seattle?

    Currently, January is the cheapest month in which you can book a flight from San Diego to Seattle (average of $238). Flying from San Diego to Seattle in July is currently the most expensive (average of $411). 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

Traveling to a place near San Diego?

Book flights to San Diego if you plan to visit one of these locations
SeaTac
Tukwila
Tacoma
Lakewood
Renton
Lacey
Ocean Shores
Leavenworth
Federal Way
Olympia
Cle Elum
Centralia
Mukilteo
Issaquah
Aberdeen
Shoreline
Lynnwood
Shelton
Silverdale
Redmond

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 San Diego to Seattle

See prices for flight routes from nearby airports that may be better suited for you.
Los Angeles to Seattle flights
Ontario to Seattle flights
San Francisco to Seattle flights
Los Angeles to Portland flights
Santa Ana to Seattle flights
San Jose to Seattle flights
Burbank to Seattle flights
Sacramento to Seattle flights
Oakland to Seattle flights
Los Angeles to Everett flights
Ontario to Portland flights
Burbank to Portland flights
Las Vegas to Seattle flights
Santa Ana to Portland flights
San Francisco to Portland flights
San Francisco to Everett flights
San Diego to Everett flights
San Jose to Portland flights
San Diego to Portland flights
Fresno to Seattle flights
Oakland to Portland flights
Santa Ana to Everett flights
Santa Rosa to Seattle flights
Sacramento to Portland flights
Los Angeles to Spokane flights
Palm Springs to Seattle flights
Las Vegas to Everett flights
Reno to Seattle flights
Santa Barbara to Seattle flights
Ontario to Spokane flights
Las Vegas to Portland flights
Long Beach to Seattle flights
San Francisco to Spokane flights
Santa Rosa to Portland flights
Fresno to Portland flights
San Diego to Spokane flights
San Luis Obispo to Portland flights
Palm Springs to Portland flights
Medford to Seattle flights
Monterey to Seattle flights
San Jose to Everett flights
San Luis Obispo to Seattle flights
Long Beach to Portland flights
San Francisco to Pasco flights
Santa Barbara to Portland flights
Reno to Portland flights
Las Vegas to Spokane flights
Fresno to Spokane flights
San Jose to Spokane flights

Top 7 airlines flying from San Diego to Seattle

Discover the top 7 airlines that operate flights from San Diego to Seattle. 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 março 21, 2025.
AirlineCheapestAverageFlexibilityOn-time
Spirit AirlinesCheapest$79Average$167FlexibilityNo cancel feeOn-time65%
FrontierCheapest$94Average$164FlexibilityNo cancel feeOn-time62%
Hawaiian AirlinesCheapest$104Average$353FlexibilityNo cancel feeOn-time85%
American AirlinesCheapest$113Average$382FlexibilityNo cancel feeOn-time71%
DeltaCheapest$117Average$243FlexibilityNo cancel feeOn-timeN/A
Alaska AirlinesCheapest$135Average$274FlexibilityNo cancel feeOn-time75%
United AirlinesCheapest$251Average$481FlexibilityNo cancel feeOn-time69%
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.