Sources have stated that high frequency EM waves are absorbed by particles in the atmosphere (such as water) more easily than low frequency EM waves. Why does this occur? Does it have anything to do with attenuation?
The absorption of radiation in the atmosphere IS attenuation. When radiation is absorbed, we've attenuated the wave.
The atmosphere is made up of different molecules that happends to absorb certain frequencies. The atmosphere on earth for example has what's called the "radio window", which means that radiawaves are passed through more or less unaffected, whereas other frequencies are not. This is partly why we have radiotelescopes on earth, but xray telescopes in orbit for example.
I hope this answers your question.