Looking for chart of UV absorption in water

[TriangleMan]

This weekend was sunny and hot in Bermuda so I was at the beach with a number of friends (for those of you in colder climates :P ). There was a discussion about using sunblock when you plan to go swimming - one of my friends figured the water would absorb the UV light so he didn't need to use sunblock. I told him that my understanding was that water didn't do a good job absorbing UV so he could still get sunburned while swimming (despite other factors such as sunlight reflecting off the water and so forth).

I started Googling information on this today and while I can find information on water absorbing UV light what I really wanted was a table that showed the absortivity of water at various wavelengths. Ten minutes later I haven't found one, there's too many links to sunscreens and water purification products. Can anyone provide a link to a chart?

[Demigrog]

I'd find a copy of the CRC Handbook of Chemistry and Physics. Any good library should have it. I don't think it is available online, at least not for free.

IIRC, swimming and boating usually increases your chances for sunburn (over, say, standing in an open field) because the surface reflects additional light. I wouldn't swear that wasn't an urban legend, but snopes doesn't list it.

[Bozola]

Absorption Spectra of Water

That it absorbs UV rather well is not very helpful.

Did you friend expect to stay completely underwater indefinitely?

[Evan]

The increase of UV from reflecting material is no urban legend. Sand, water, snow and clouds as well as altitude can all greatly increase UV exposure. The worst case here is a brilliant sunny winter day on a mountain with large scattered clouds and snow on the ground. There is a good reason the Inuit people developed snow goggles.

See Snow goggles.

[John Jones]

I'll second that recommendation of the CRC Handbook of Chemistry and Physics. Don't let the title fool you -- it may be the fattest book you ever saw.

It is available on-line, but by subscription.


http://www.hbcpnetbase.com/home.asp

Again, any decent llibrary should have it.

Hang around the chemistry/physics department of a local university, and you may find it for sale at a good price. We used to sell them as a fund-raising activity.

[TriangleMan]

Absorption Spectra of Water
That it absorbs UV rather well is not very helpful.

Thanks for the link, it was what I was looking for! I read the charts though and it looks to me that water didn't absorb UV very well - the middle chart in your link shows penetration of 1m-10m through water (with the lowest point being in the visible spectrum (blue). Am I reading this incorrectly?

Did you friend expect to stay completely underwater indefinitely?

My friend just had the logic of "if only my head is above water then there will be at least a few inches of water protecting my shoulders, which should be as effective a UV protectant as a layer of sunscreen". He was wearing a shirt while on the beach but took it off to go swimming and figured being in water would protect his torso and shoulders from UV.

[TriangleMan]

I'd find a copy of the CRC Handbook of Chemistry and Physics. Any good library should have it.

Given my location the local library probably won't have it but I'm sure the Biological Research Station or the local college should have one. I'll check there.

IIRC, swimming and boating usually increases your chances for sunburn (over, say, standing in an open field) because the surface reflects additional light.

That's not the issue though, its whether the parts of your body under the water are protected from UV. Granted, the reflection of the sunlight off the water (which is dependent on the angle of the Sun) would play a factor, as would other things such as absorption by other substances in the ocean (algae, salt, small particles of sand), but I just wanted to see how well the water itself would protect from UV.

[TriangleMan]

Hang around the chemistry/physics department of a local university, and you may find it for sale at a good price. We used to sell them as a fund-raising activity.

I'm not even sure if the local college even has a chemistry/physics department. It's a two-year college and any sciences would be geared to biology so it would offer chemistry courses but I don't think it would have its own department. I've never seen a CRC Handbook for sale on this island either. They definately should have one though.

[frogesque]

My own thoughts so I have no data for back up.

Water, especially salt water will readily leech natural oils from the skin so without a waterproof sun block you loose what natural protection you have.

Most people swim or doggy paddle at a very shallow depth, head and shoulders mostly exposed so UV absorbtion by the water would be irrelevent.

Emerging from the water you also get water droplets focusing the sun's rays directly onto the skin (I'm assuming the effect would be simmilar to watering plants on a sunny day and then getting leaf burn) Coupled with reflection off the water surface it's my guess that you would be getting a 40-50% extra radiation dose and those point water droplet burns would pentrate the epidermis and cause deep burning.

Dry salt and sand are very abrasive and would tend to scarify the dead outer protective skin layer after toweling down leaving the new skin exposed and vulnerable.

For the record I got sunburnt one sunny day in January on a Scottish beach near me. I was sitting sheltered from the wind facing the sun watching seals. I have the kind of skin type that's very sensitive to sunburn.

Like smoking, it's your friend's body and he can do what he likes with it. Me? I would wear a block and keep a shirt on.