Painting over a popcorn ceiling is a way to "encapsulate" asbestos, which will contain it. Spray paint is best so that you don't disturb the popcorn ceiling and make it crumble. Make sure to vacuum the ceiling first to remove any loose particles, then use an oil-based primer before you apply any paint. An acrylic latex paint is ideal. If you use a sprayer with a tip size that's 517 of 617, you'll be more quick and efficient with your project.