import cdsapi
c = cdsapi.Client()
c.retrieve(
    'cams-global-atmospheric-composition-forecasts',
    {
        'date': '2021-03-24',
        'time': [
            '00:00', '06:00', '12:00',
            '18:00',
        ],
        'leadtime_hour': '0',
        'area': [           #North, West, South, East
            70, -18, 69,
            -17,
        ],
        'type':'analysis',
        'variable': 'total_aerosol_optical_depth_670nm',
        'format': 'netcdf_zip',
    },
    'download.netcdf_zip')