Consider the following statements:

1. The World Health Organization's 2021 Air Quality Guidelines prescribe stricter PM2.5 limits than the earlier 2005 guidelines.

2. Ground-level ozone concentrations typically peak during cold, overcast weather.

3. PM10 particles are small enough to pass into the bloodstream through the lungs.

4. Prolonged exposure to ground-level ozone can trigger or worsen asthma.

How many of the statements given above are correct?