Outdoors will be much better, as anything aerosolized will disperse much quicker and over a larger area. Compare it to a fart or someone wearing a ton of bad perfume: outdoors you may barely notice it, while inside it hits you for an hour. Even if you're wearing a mask! This website, NE Journal of Medicine, has a study on viral viability. Here's the quick points:
We evaluated the stability of SARS-CoV-2 and SARS-CoV-1 in aerosols and on various surfaces and estimated their decay rates using a Bayesian regression model
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The inoculum resulted in cycle-threshold values between 20 and 22, similar to those observed in samples obtained from the upper and lower respiratory tract in humans.
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SARS-CoV-2 remained viable in aerosols throughout the duration of our experiment (3 hours), with a reduction in infectious titer from 10^3.5 to 10^2.7 TCID50 per liter of air.
So I'm reading this as they started with a dosage of aerosols similar to what a person would breathe out, I have no idea on how many breaths worth of sample they did. TCID50 is "50% tissue-culture infectious dose", which sounds like it's a sufficient quantity of viri to cause an infection to start in their culture sample 50% of the time. Their aerosol test only ran for three hours (?), and it went from 3000x the infectious dose, down to 500x the infectious dose. This is PER LITER OF AIR, and for reference, a 10'x10' room with 8' ceilings has 22,000 liters of air. So, those numbers are a lot more dispersed, but also real life will have a lot more breathing (and possibly more people) to add continuing aerosol amounts. I believe they mention it's a logarithmic decrease, so as your number gets smaller, it gets smaller slower (could be days+ to get below the 1x TCID50), but you also have less chance of walking into it. And, I assume this study looked at a closed-air system, so your house/grocery with running HVAC/windows/open doors will likely cause those to get filtered/pushed out somewhat quicker.
We actually just had a REME HALO® air purifier installed (~$750), and there's definitely noticeably cleaner air downstairs. No, this had nothing to do with the ChinaVirus, it was for the wife's excessive allergies. Of which she did not mention before marriage...
If we look at mask efficiency, this study: https://pubmed.ncbi.nlm.nih.gov/32329337/ gives us some decent charts. But, before we glance at that, I'll give you THIS and THIS, which tell us that a good 80-90% of droplets you breathe out, are one micrometer or smaller. (Which is the 10^3nm line in the chart.) (Coughing/Sneezing will have a larger amount of bigger droplets, mostly 2-24μm.) Masks. Here's a chart from the big link;
If we look at the bottom chart, you'll notice that those mask efficiencies drop from ~98% down to 30-40% simply from a lack of seal. Which, NO ONE has, that I've seen. Maybe 2-3 people wearing a full face respirator, but I doubt they had fresh canisters, if they even had it properly sealed.
I'm not sure why they didn't test the N95 gap/no-gap, since that's the main mask CDC recommends (though most people wear surgical-style masks, which can't seal). Unless, the N95 on top is the same as the surgical mask on the bottom, as their graph lines are similar.
So, long story short, there are plenty of infectious doses around, masks will barely help you outside of coughs/sneezes, and the surrounding environment will spread it out much better (good or bad point here). From other stuff I've seen, the most effective removal medium is high humidity, which makes sense.