The direct (albedo) effect is generally to cool the planet; the indirect effect (the particles act as cloud condensation nuclei and thereby change cloud properties) is less certain.
ðə dᵻɹˈɛkt ælbˈiːdoʊ ɪfˈɛkt ɪz dʒˈɛnɚɹəli tə kˈuːl ðə plˈænɪt; ðɪ ˌɪndɚɹˈɛkt ɪfˈɛkt ðə pˈɑːɹɾɪkəlz ˈækt æz klˈaʊd kɑːndɛnsˈeɪʃən nˈuːklɪi ænd ðɛɹbˈaɪ tʃˈeɪndʒ klˈaʊd pɹˈɑːpɚɾiz ɪz lˈɛs sˈɜːʔn̩.