It's actually more mixed than you would think since it forms HCl in the atmosphere and falls down with rain.

For reference 1 inch of rain over 1 sq. mile is approximately 18 million gallons.

So even if we concentrated the full 250k gallons (remember that HCl is just one byproduct too, so we are being very generous with 250k gallons, most of the byproducts are carbon monoxide/dioxide), but 250k gallons into 1 sq mile of rain fall....138ppm

In reality this will fall over thousands of square miles too.