Cryptic crossword

ACROSS

1. Do much better than pupils in the open air? (8) 5. She gives help to a thousand (4) 9. I object to article which is low (4) 10. Potentially explosive journal? (8) 11. The French doctor with no head for fruit (5) 12. Hanging around, monarch finds bird sound lacking in colour (7) 13. What Adam’s ale might make an alcoholic? (2,4,2,5) 18. What the ark may have been for tourists? (8) 19. Helps, because I would be in it (4) 20. This flower could be a big one (7) 21. 11’s other fruit (5) 22. The last big things in the car? (4) 23. Sound one’s aitches like a buccaneer? (8)

DOWN

2. It’s no good to reduce one’s intake! (7) 3. Offer comfort at the organ? (7) 4. Letters from the lesser chief cities (5,8) 6. Nature worshipper provides its main problem (7) 7. Doctor on the brink of taking redhead on digger (7) 8. One vegetable may spoil a whole line (6) 13. Pleasant, like a loud story? (7) 14. Red gown badly treated (7) 15. Intense study in painting (6) 16. A graduate, true, is different - he’s not professional! (7) 17. Extreme finish to the greater part (7)