As mentioned all air must pass through your filter and to do this with an open window you'd need to create negative pressure. If your intake is too big then you can't achieve this and you will have a leak...may not necessarily be your filter although I'd definitely consider it to be the culprit. You can shake the filter to fill any voids created in the carbon over time and if that doesn't work..drill the filter so you can refill it or replace it altogether. You can also double up on a filter if you really want to
Just closed opposite window. We are building cabin pressure, negative pressure. Just learned about it in this thread too. Ya know kids, I'm a farmer. (Wait, that's from woodstock) Yes, I'm a farmer. And pre-internet, for 20 years outside (in a different town ) I got the seediest crop each year (always one tiny male would impregnate the entire garden. I'd find him too late, smoking a cigar.) When the fall came, I would try to ADD light. Didn't make sense that 12 and 12 (less sunlight) produced the preferred feminine product.
If I knew then what I do now, I would have had a lot of seedless dewbage, enough to not have streetlamps in the house all winter and summer long.