[Fixed]-APIView stopping another view from working

Anything that matches (?P<poll>\w+d+) will be matched first by (?P<url>\w+), so the site_daily_means view will run.

You could fix this by changing the url pattern for pollutant_daily_means, e.g. to:

url(r'^api/daily-means/poll/(?P<poll>\w+d+)/', views.pollutant_daily_means.as_view()),

Note that \w+\d+ is probably unnecessary in this case. You could simplify it to \w+ since you already filter DailyMean on the poll field.