Cheap flights from Cedar Rapids to San Diego (CID - SAN) from $60

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 4/20. Fares are subject to change and may not be available on all flights or dates of travel. Click the price to replicate the search for this deal.
CID — SAN
Feb 27 — Mar 51

The best prices from Cedar Rapids to San Diego are usually found in October or November, booked 20 days in advance, depart on a Saturday or Wednesday and return on a Friday

Cheap flight deals from Cedar Rapids to San Diego

Discover tips and strategies to find the most affordable flight options for your journey from Cedar Rapids (CID) to San Diego (SAN). 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 February 22, 2024.

Popular in

July

Cheapest in

October

Round-trip from

$288

One-way from

$259
High demand for flights, 22% potential price rise
Best time to find cheap flights, 19% potential price drop
From Cedar Rapids to San Diego
One-way flight from Cedar Rapids to San Diego

What is the cheapest day to fly round-trip from Cedar Rapids to San Diego?

Saturday flights are generally found to be more expensive for flights from Cedar Rapids to San Diego. This shouldn’t discourage you from searching, as you can still find great deals by being flexible with your options. Use our search form to find deals on tickets to San Diego.

How far in advance should I book a flight from Cedar Rapids to San Diego?

Travelers have found it’s best to book a flight 21 days in advance to save up to 296% compared to booking the same week of travel. As your travel date approaches, the cost of this flight route may potentially increase. While opting to book 21 days out may not be an option for all, there are still additional ways to secure a deal in the near future. You might find a flight from Cedar Rapids to San Diego 1-2 weeks in advance for as low as $591, or $647 for flights within the next 24 hours.

What is the cheapest month to fly from Cedar Rapids to San Diego?

Flights from Cedar Rapids to San Diego lean towards being more expensive in July. Prices are generally better when you fly from Cedar Rapids to San Diego in October, with the cheapest ticket starting at $128.

When is the cheapest time to fly from Cedar Rapids to San Diego (CID - SAN)?

A simple way to save on the total cost of your ticket is to fly from Cedar Rapids to San Diego in the evening. If you’re flexible enough to do this you can expect to save up to 14% on your trip compared to booking a flight in the afternoon.

Cheap Frontier flights from Cedar Rapids to San Diego

Explore cheap flight options specifically provided by Frontier for the route between Cedar Rapids and San Diego. Find affordable fares and compare prices with other airlines to secure the best deal for your journey. Over the last 7 days, Cheapflights users made 3,442,422 searches. Data last updated February 22, 2024.
Take a look at some of the lowest-priced Frontier flights heading from Cedar Rapids to San Diego. Be sure to come back soon if the deals available don't appeal to you at this time.
Sat 5/43:58 pmCID - SAN
1 stop6h 17mFrontier
Wed 5/86:15 pmSAN - CID
1 stop20h 20mFrontier
Deal found 2/21$202
Sat 5/43:58 pmCID - SAN
1 stop6h 17mFrontier
Wed 5/89:32 pmSAN - CID
2 stops17h 03mFrontier
Deal found 2/21$233
Sat 4/203:58 pmCID - SAN
1 stop6h 17mFrontier
Sat 4/279:33 amSAN - CID
1 stop29h 00mFrontier
Deal found 2/21$237
Wed 4/175:17 pmCID - SAN
1 stop16h 46mFrontier
Sat 4/204:57 pmSAN - CID
1 stop21h 36mFrontier
Deal found 2/21$246
Fri 5/35:42 pmCID - SAN
1 stop16h 50mFrontier
Wed 5/86:15 pmSAN - CID
1 stop20h 20mFrontier
Deal found 2/21$262
Wed 4/105:35 pmCID - SAN
1 stop19h 56mFrontier
Sun 4/144:30 pmSAN - CID
1 stop22h 22mFrontier
Deal found 2/21$268
Wed 5/85:12 pmCID - SAN
1 stop20h 25mFrontier
Sat 5/112:19 pmSAN - CID
1 stop24h 14mFrontier
Deal found 2/21$274
Mon 4/83:50 pmCID - SAN
1 stop19h 26mFrontier
Mon 4/159:23 amSAN - CID
1 stop5h 29mFrontier
Deal found 2/21$285
Fri 5/35:42 pmCID - SAN
1 stop16h 50mFrontier
Tue 5/710:05 pmSAN - CID
2 stops16h 12mFrontier
Deal found 2/21$294

Cheap Delta flights from Cedar Rapids to San Diego

Explore cheap flight options specifically provided by Delta for the route between Cedar Rapids and San Diego. Find affordable fares and compare prices with other airlines to secure the best deal for your journey. Over the last 7 days, Cheapflights users made 3,442,422 searches. Data last updated February 22, 2024.
Some of the best deals we've found on Delta flights traveling from Cedar Rapids to San Diego. Ensure the flight price, dates, time, and airline match your criteria before you book.
Sat 4/207:05 amCID - SAN
2 stops9h 19mDelta
Wed 4/242:16 pmSAN - CID
1 stop7h 37mDelta
Deal found 2/21$303
Sat 4/207:05 amCID - SAN
2 stops9h 19mDelta
Wed 4/2410:10 amSAN - CID
2 stops10h 25mDelta
Deal found 2/21$308
Thu 7/44:15 pmCID - SAN
1 stop6h 14mDelta
Fri 7/53:00 pmSAN - CID
1 stop5h 25mDelta
Deal found 2/21$328
Wed 5/227:05 amCID - SAN
1 stop8h 15mDelta
Wed 5/296:15 amSAN - CID
1 stop7h 14mDelta
Deal found 2/21$358
Wed 5/227:05 amCID - SAN
2 stops9h 19mDelta
Wed 5/296:15 amSAN - CID
1 stop7h 14mDelta
Deal found 2/21$363
Wed 5/17:05 amCID - SAN
1 stop7h 46mDelta
Wed 5/811:00 amSAN - CID
2 stops9h 28mDelta
Deal found 2/21$373
Mon 5/64:09 pmCID - SAN
1 stop6h 12mDelta
Sat 5/1111:10 amSAN - CID
2 stops9h 18mDelta
Deal found 2/21$374
Tue 4/304:09 pmCID - SAN
1 stop6h 12mDelta
Wed 5/86:15 amSAN - CID
2 stops14h 13mDelta
Deal found 2/21$376
Sat 5/47:05 amCID - SAN
2 stops11h 05mDelta
Wed 5/811:00 amSAN - CID
2 stops9h 28mDelta
Deal found 2/21$378

Cheap Cedar Rapids to San Diego flights in February & March 2024

Find cheap flight options from Cedar Rapids to San Diego specifically for the months of February and March 2024. Explore affordable fares based on user searches. Over the last 7 days, Cheapflights users made 3,442,422 searches. Prices were last updated on February 22, 2024.
The lowest fares we've come across on flights traveling from Cedar Rapids to San Diego in February and March 2024. More deals are always being added, so be sure to check back regularly.
Wed 3/68:32 pmCID - SAN
1 stop13h 45mFrontier
Tue 3/129:07 amSAN - CID
1 stop27h 53mFrontier
Deal found 2/21$297
Wed 3/68:32 pmCID - SAN
1 stop13h 45mFrontier
Tue 3/125:51 pmSAN - CID
1 stop19h 09mFrontier
Deal found 2/21$298
Fri 2/239:35 pmCID - SAN
1 stop21h 38mFrontier
Sun 2/256:25 amSAN - CID
1 stop26h 27mFrontier
Deal found 2/20$301
Wed 3/68:32 pmCID - SAN
1 stop13h 45mFrontier
Tue 3/127:27 pmSAN - CID
2 stops17h 33mFrontier
Deal found 2/21$319
Tue 3/52:14 pmCID - SAN
1 stop24h 31mMultiple Airlines
Tue 3/125:51 pmSAN - CID
1 stop19h 09mMultiple Airlines
Deal found 2/21$326
Mon 3/113:50 pmCID - SAN
1 stop18h 27mMultiple Airlines
Tue 3/1210:28 pmSAN - CID
2 stops14h 32mMultiple Airlines
Deal found 2/21$335
Wed 3/68:32 pmCID - SAN
1 stop13h 45mMultiple Airlines
Sun 3/1010:59 pmSAN - CID
1 stop11h 35mMultiple Airlines
Deal found 2/21$370
Mon 3/111:24 pmCID - SAN
1 stop8h 51mMultiple Airlines
Tue 3/125:51 pmSAN - CID
1 stop19h 09mMultiple Airlines
Deal found 2/21$378
Mon 3/111:24 pmCID - SAN
1 stop8h 51mMultiple Airlines
Tue 3/125:51 pmSAN - CID
1 stop19h 09mMultiple Airlines
Deal found 2/21$379

Cedar Rapids to San Diego 2024 flight deals

Discover exclusive flight deals for travel between Cedar Rapids and San Diego in 2024. Find excellent offers based on user searches. Over the last 7 days, Cheapflights users made 3,442,422 searches. Data last updated February 22, 2024.
The lowest fares we've come across on flights traveling from Cedar Rapids to San Diego in February and March 2024. More deals are always being added, so be sure to check back regularly.
Sat 5/43:58 pmCID - SAN
1 stop6h 17mFrontier
Wed 5/86:15 pmSAN - CID
1 stop20h 20mFrontier
Deal found 2/21$202
Sat 5/43:58 pmCID - SAN
1 stop6h 17mFrontier
Wed 5/89:32 pmSAN - CID
2 stops17h 03mFrontier
Deal found 2/21$233
Sat 4/203:58 pmCID - SAN
1 stop6h 17mFrontier
Sat 4/279:33 amSAN - CID
1 stop29h 00mFrontier
Deal found 2/21$237
Wed 4/175:17 pmCID - SAN
1 stop16h 46mFrontier
Sat 4/204:57 pmSAN - CID
1 stop21h 36mFrontier
Deal found 2/21$246
Fri 5/35:42 pmCID - SAN
1 stop16h 50mFrontier
Wed 5/86:15 pmSAN - CID
1 stop20h 20mFrontier
Deal found 2/21$262
Wed 4/105:35 pmCID - SAN
1 stop19h 56mFrontier
Sun 4/144:30 pmSAN - CID
1 stop22h 22mFrontier
Deal found 2/21$268
Wed 5/85:12 pmCID - SAN
1 stop20h 25mFrontier
Sat 5/112:19 pmSAN - CID
1 stop24h 14mFrontier
Deal found 2/21$274
Mon 4/83:50 pmCID - SAN
1 stop19h 26mFrontier
Mon 4/159:23 amSAN - CID
1 stop5h 29mFrontier
Deal found 2/21$285
Fri 5/35:42 pmCID - SAN
1 stop16h 50mFrontier
Tue 5/710:05 pmSAN - CID
2 stops16h 12mFrontier
Deal found 2/21$294

Cedar Rapids to San Diego flights leaving soon

Find last-minute flight options from Cedar Rapids to San Diego for spontaneous travel. Discover available flights and compare prices based on user searches. Secure great deals and offers for spontaneous trips with quick booking options. Over the last 7 days, Cheapflights users made 3,442,422 searches. Data last updated February 22, 2024.
Check out these flights departing soon from Cedar Rapids to San Diego. To prevent any unwanted surprises, users should verify their flight info before booking.
Wed 3/68:32 pmCID - SAN
1 stop13h 45mFrontier
Tue 3/129:07 amSAN - CID
1 stop27h 53mFrontier
Deal found 2/21$297
Wed 3/68:32 pmCID - SAN
1 stop13h 45mFrontier
Tue 3/125:51 pmSAN - CID
1 stop19h 09mFrontier
Deal found 2/21$298
Fri 2/239:35 pmCID - SAN
1 stop21h 38mFrontier
Sun 2/256:25 amSAN - CID
1 stop26h 27mFrontier
Deal found 2/20$301
Wed 3/68:32 pmCID - SAN
1 stop13h 45mFrontier
Tue 3/127:27 pmSAN - CID
2 stops17h 33mFrontier
Deal found 2/21$319
Tue 3/52:14 pmCID - SAN
1 stop24h 31mMultiple Airlines
Tue 3/125:51 pmSAN - CID
1 stop19h 09mMultiple Airlines
Deal found 2/21$326
Wed 3/68:32 pmCID - SAN
1 stop13h 45mMultiple Airlines
Sun 3/1010:59 pmSAN - CID
1 stop11h 35mMultiple Airlines
Deal found 2/21$370
Wed 3/68:32 pmCID - SAN
1 stop13h 45mMultiple Airlines
Wed 3/135:53 pmSAN - CID
1 stop15h 58mMultiple Airlines
Deal found 2/21$413
Wed 3/68:32 pmCID - SAN
1 stop13h 45mMultiple Airlines
Wed 3/1310:28 pmSAN - CID
1 stop11h 23mMultiple Airlines
Deal found 2/21$419
Tue 3/56:50 amCID - SAN
1 stop7h 43mDelta
Tue 3/122:25 pmSAN - CID
1 stop6h 08mDelta
Deal found 2/21$423

One-way flights to San Diego from Cedar Rapids

Search for one-way flight options from Cedar Rapids to San Diego. Find affordable one-way fares based on user searches. Compare prices and availability to plan your one-way journey according to your preferred dates and budget. Over the last 7 days, Cheapflights users made 3,442,422 searches. Data last updated February 22, 2024.
Some of the best available deals we've found on one-way flights from Cedar Rapids to San Diego. Those seeking round-trip flights from Cedar Rapids to San Diego should utilize the search form at the the top of the page.
Sat 4/203:58 pmCID - SAN
1 stop6h 17mFrontier
Deal found 2/21$60
Thu 4/185:30 pmCID - SAN
1 stop16h 38mFrontier
Deal found 2/21$166
Sat 4/203:58 pmCID - SAN
2 stops26h 37mMultiple Airlines
Deal found 2/21$171
Sat 4/203:58 pmCID - SAN
3 stops21h 47mMultiple Airlines
Deal found 2/21$187
Fri 5/312:21 pmCID - SAN
1 stop8h 19mFrontier
Deal found 2/21$189
Thu 4/185:30 pmCID - SAN
2 stops23h 51mFrontier
Deal found 2/21$192
Sat 6/13:52 pmCID - SAN
1 stop6h 12mFrontier
Deal found 2/21$194
Mon 6/32:21 pmCID - SAN
1 stop18h 03mFrontier
Deal found 2/21$211
Tue 4/166:00 amCID - SAN
1 stop8h 51mDelta
Deal found 2/21$214

Find flights from Cedar Rapids to San Diego within your budget

Customize your flight search to find flights from Cedar Rapids to San Diego 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 3,442,422 searches. Data last updated February 22, 2024.

Fly from

Any airport

Fly to

Any airport

Budget

$202 - $480

Route

Depart

Return

Price

Cedar RapidsSan Diego

CID - SAN

CIDSAN

Cedar Rapids

Sat 5/4

1 stop6h 17m

San Diego

Wed 5/8

1 stop20h 20m

$202

Cedar RapidsSan Diego

CID - SAN

CIDSAN

Cedar Rapids

Sat 5/4

1 stop6h 17m

San Diego

Wed 5/8

2 stops17h 03m

$233

Cedar RapidsSan Diego

CID - SAN

CIDSAN

Cedar Rapids

Sat 4/20

1 stop6h 17m

San Diego

Sat 4/27

1 stop29h 00m

$237

Cedar RapidsSan Diego

CID - SAN

CIDSAN

Cedar Rapids

Wed 4/17

1 stop16h 46m

San Diego

Sat 4/20

1 stop21h 36m

$246

Cedar RapidsSan Diego

CID - SAN

CIDSAN

Cedar Rapids

Sat 4/20

2 stops9h 19m

San Diego

Wed 4/24

1 stop7h 37m

$303

Cedar RapidsSan Diego

CID - SAN

CIDSAN

Cedar Rapids

Sat 4/20

2 stops9h 19m

San Diego

Wed 4/24

2 stops10h 25m

$308

Cedar RapidsSan Diego

CID - SAN

CIDSAN

Cedar Rapids

Tue 3/5

1 stop24h 31m

San Diego

Tue 3/12

1 stop19h 09m

$326

Cedar RapidsSan Diego

CID - SAN

CIDSAN

Cedar Rapids

Wed 5/1

2 stops20h 37m

San Diego

Sat 5/4

2 stops12h 36m

$446

Cedar RapidsSan Diego

CID - SAN

CIDSAN

Cedar Rapids

Wed 3/20

1 stop9h 52m

San Diego

Wed 3/27

1 stop16h 09m

$480

Flights are sorted by cheapest first

Deals found on 2/21

When is the best time to book a flight from Cedar Rapids to San Diego?

Use this chart to determine the optimal time to book a round-trip flight from Cedar Rapids to San Diego. Price data was last updated on January 28, 2024.
To ensure you get the cheapest price possible for a flight from Cedar Rapids to San Diego, you should look to book at least 20 days in advance of your intended travel date. The price of your flight may increase if you delay and leave booking until a week or so before departure.
Search Deals

When is the cheapest time to fly from Cedar Rapids to San Diego?

Use this chart to determine the cheapest time to fly round-trip from Cedar Rapids to San Diego. Price data was last updated on February 18, 2024.
Morning
Noon
Afternoon
Evening
All times are departure.
Travelers seeking maximum savings on their Cedar Rapids to San Diego flight should consider departing on Tuesday evenings when fares are most often at their lowest. Monday afternoons flights should be avoided if possible as fares are typically the most expensive at this time.
Search Deals

Average price of flights to San Diego by month

Plan your trip from Cedar Rapids to San Diego by taking into account the cheapest months to travel. The average price of a one-way flight from Cedar Rapids to San Diego is currently $176 while a round-trip flight costs $309. Price data was last updated on February 18, 2024.

Currently, October is the cheapest month in which you can book a flight from Cedar Rapids to San Diego (average of $288). Flying from Cedar Rapids to San Diego in June is currently the most expensive (average of $386). 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.

January

$292

February

$297

March

$336

April

$338

May

$338

June

$386

July

$372

August

$315

September

$302

October

$288

November

$331

December

$305

Temperature and rainfall in San Diego by month

Plan your trip to San Diego by taking into account the average temperature and rainfall totals by month.

SAN

Temperature

57.2 - 71.6 °F

Reviews of airlines servicing San Diego

Get insights into the airlines that provide service to San Diego. 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 San Diego. Reviews last updated February 22, 2024.
To help decide which airline to fly from Cedar Rapids to San Diego, see what other customers have to say about Frontier, Delta and United Airlines. You can also see how each airline stacks up in terms of entertainment options, comfort, food, crew/service, and boarding process.
8.1
Very good
11,921 reviews

Comfort

7.9

Overall

8.1

Crew

8.6

Entertainment

8.1

Food

7.5

Boarding

8.2

Reviews

1 / 10

Crew was nice and courteous. Boarding went smoothly. But we experienced a few minutes of extreme turbulence.

8.1
Very good
11,921 reviews
8.1
Very good
11,921 reviews

Comfort

7.9

Overall

8.1

Crew

8.6

Entertainment

8.1

Food

7.5

Boarding

8.2

Reviews

1 / 10

Crew was nice and courteous. Boarding went smoothly. But we experienced a few minutes of extreme turbulence.

7.4
Good
11,872 reviews
8.1
Very good
11,921 reviews

Comfort

7.9

Overall

8.1

Crew

8.6

Entertainment

8.1

Food

7.5

Boarding

8.2

Reviews

1 / 10

Crew was nice and courteous. Boarding went smoothly. But we experienced a few minutes of extreme turbulence.

7.3
Good
15,643 reviews
8.1
Very good
11,921 reviews

Comfort

7.9

Overall

8.1

Crew

8.6

Entertainment

8.1

Food

7.5

Boarding

8.2

Reviews

1 / 10

Crew was nice and courteous. Boarding went smoothly. But we experienced a few minutes of extreme turbulence.

6.4
Okay
4,512 reviews
8.1
Very good
11,921 reviews

Comfort

7.9

Overall

8.1

Crew

8.6

Entertainment

8.1

Food

7.5

Boarding

8.2

Reviews

1 / 10

Crew was nice and courteous. Boarding went smoothly. But we experienced a few minutes of extreme turbulence.

Related info for your journey

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

Can I find flights from Cedar Rapids to San Diego for under $300 on Cheapflights?

Yes, there are multiple flights from Cedar Rapids to San Diego for under $300. The cheapest flight booked recently is on Frontier for just $202, but on average you can expect to pay $287.

Are there last-minute flights available from Cedar Rapids to San Diego for under $300?

There are currently 20+ open flights from Cedar Rapids to San Diego within the next 7 days for less than $300.

What are the cheapest airlines flying from Cedar Rapids to San Diego round-trip?

Our cheapest airline available from Cedar Rapids to San Diego is Frontier. Our recent data shows that you can find tickets from as low as $202 on this airline. An additional option worth looking into is Delta, starting at $303. Frontier is priced at 61% lower than the current average price of a flight leaving 3 months from now.

What are the cheapest airlines to fly from Cedar Rapids to San Diego one-way?

For one-way options, check prices for Frontier. According to our data, you can fly for as low as $60. Users have also found prices from $214 and $458 on Delta and United Airlines, respectively.

What are the most popular airlines that fly from Cedar Rapids to San Diego?

What does CID to SAN mean?

Cedar Rapids Airport is CID and San Diego Airport is SAN. These codes are created by the International Air Transport Association (IATA) and airlines use them to identify the departing and arrival airports in the flight routes they service.

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.

Top 4 airlines flying from Cedar Rapids to San Diego

Discover the top 4 airlines that operate flights from Cedar Rapids to San Diego. 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 3,442,422 searches. Data last updated February 22, 2024.
AirlineCheapestAverageFlexibilityOn-time
FrontierCheapest$118Average$212FlexibilityNo cancel feeOn-time62%
Search Frontier flights
American AirlinesCheapest$282Average$468FlexibilityNo cancel feeOn-time71%
Search American Airlines flights
DeltaCheapest$296Average$486FlexibilityNo cancel feeOn-timeN/A
Search Delta flights
United AirlinesCheapest$324Average$519FlexibilityNo cancel feeOn-time69%
Search United Airlines flights

Search flights from Cedar Rapids to San Diego by cabin class

Find flights from Cedar Rapids to San Diego, based on your preferred cabin class, be it economy, premium economy, business, or first class.

Book a flight to one of these trending destinations

User searches for flights to these destinations increased 20% or more in the past 90 days compared to other destinations

Fly with Cheapflights

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

How does Cheapflights help users find flights from Cedar Rapids to San Diego?

Cheapflights makes it easy to find Cedar Rapids to San Diego flights 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 Cedar Rapids to San Diego?

Cheapflights simply makes it quick and affordable to book flights from Cedar Rapids to San Diego by bringing together all flight options from hundreds of airlines and agencies online — and put it in one place for you to choose from. Plus, Cheapflights is 100% free to use for all.

Can Cheapflights find flights from Cedar Rapids to San Diego with no change fees?

Need flexible booking options for your flight to San Diego from Cedar Rapids? 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 Cedar Rapids to San Diego become cheaper?

Of course! You can now track prices for flights from Cedar Rapids to San Diego and get an alert from Cheapflights when they change. Have a valid email address ready and click the bell icon next to the flight deals above to set up your price alerts.

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.