ACROSS
 8. <encryption> CIPHER = IP inside CHER
 9. <covered up> OBSCURED = OD outside BS CURE
10. <piece of machinery> GEAR = G EAR
11. <chemically disinfect> CHLORINATE = REACTION* outside HL
12. (.t)ARTINES S(i.) = ARTINESS <cultural sophistication>
14. ←CID _RON_← = NORDIC <from Scandinavia>
16. <focused on people> ANTHROPOCENTRIC = HR inside CONTRACEPTION*
19. C ODD L _E = CODDLE <baby>
21. <recording> CASSETTE = C AS SET + THE - H
23. "E-CIG" + NATURE = E-SIGNATURE <ID>
25. <queen's clothes> DRAG <are boring>
27. D_ EMERITUS - U = DEMERITS <negative marks>
28. DR inside TUNA = TUNDRA <icy region>

DOWN
 1. + G, I'VE = GIVE <yield>
 2. <bad-tempered> CHURLISH = C HURL IS H
 3. <daycare> CRECHE = C + REC _HE_
 4. <way ...> COLLISION COURSE {route where we'll definitely collide}
 5. SERGEANT* = ESTRANGE <to cause resentment>
 6. _D _U_N_N_ _E _R = DUNNER <bailiff, perhaps>
 7. "SCENT" = CENT <penny>
13. <nobody in particular> RANDO = RAN DO
15. <fool> IDIOT = ←(.c)TOID I(n.)←
17. <theatrical> OPERATIC = O + EPIC* outside RAT
18. <viral> TRENDING = ←RT← ENDING
20. <stubborn> DOGGED = ←D_ EG GOD←
22. <sleek> SVELTE = LT inside S VEE
24. ←CEPS← = SPEC <detailed instructions>
26. <atmosphere> AURA = AURA[-l]