If you are interested in making a career out of this as opposed to going on an adventure, that is a whole different kettle of fish. First piece of advice - don't apply for a masters program, apply for a PhD program. As the PI on these sorts of programs, masters students are of little use to me as Research Assistants as it takes a year or two to get a student up to speed - at which point a masters student is leaving. A PhD student still has 3-4 years left, which is when they provide the most value to the research project, and when the students gets the most out of it. If you decide the field is not for you, you can still leave with a masters after the completion of your comprehensive exams 2-3 years in.
Second, this is only the a road I would go down if you are truly and primarily interested in the science, not the field work. For every month in the field, there is a year or more in the lab and in front of a computer calibrating instruments, writing code, analyzing data, and writing the papers - which is after all the ultimate goal of the work. If you are really interested in just the field work part, a technician or support staff path maybe a more appropriate position. NEON is often hiring for this sort of position to support their network of ecological/hydrological/meteorological field sites.
I would still recommend one of these adventure/educational tourism options as a first step to try out this sort of thing before committing many years of your life to getting a PhD. A couple thousand dollars and few weeks is a small price to pay to test out the career.
I don't mean to sound discouraging, but we get many folks who think this is the career for them, but once they actually face the reality of turning the data they collected into a meaningful scientific result they become less excited.
If you are interested in air quality and geoinformatics, openaq.org would be a good place to spend some time.