Type 1 active galactic nuclei display broad emission lines, regarded as arising from photoionized gas moving in the gravitational potential of a supermassive black hole 1, 2 . The origin of this broad-line region gas is unresolved so far 1, 2, 3 , however. Another component is the dusty torus 4 beyond the broad-line region, likely an assembly of discrete clumps 5, 6, 7 that can hide the region from some viewing angles and make them observationally appear as Type 2 objects. Here we report that these clumps moving within the dust sublimation radius, like the molecular cloud G2 discovered in the Galactic center 8 , will be tidally disrupted by the hole, resulting in some gas becoming bound at smaller radii while other gas is ejected and returns to the torus. The clumps fulfill necessary conditions to be photoionized 9 . Specific dynamical components of tidally disrupted clumps include spiral-in gas as inflow, circularized gas, and ejecta as outflow. We calculate various profiles of emission lines from these clouds, and find they generally agree with Hβ profiles of Palomar-Green quasars 10 . We find that asymmetry, shape and shift of the profiles strongly depend on [O III] luminosity, which we interpret as a proxy of dusty torus angles. Tidally disrupted clumps from the torus may represent the source of the broad-line region gas. The mass of individual clumps can be estimated by the tidal disruption condition at the dust sublimation radius given by the inner edge of torus, D sub ≈ 0.4 L 1/2 45 T −2.6 1500 pc, where L 45 = L UV /10 45 erg s −1 and T 1500 = T sub /1500K is the dust sublimation temperature 11, 6, 12 . The tidal disruption happens at or inside the Roche limit of D tid = (M • /M C ) 1/3 R C , where M • is the black hole mass, M C is the clump mass, and R C = (M C /πN H m p ) 1/2 is the size, where N H is the column density and m p is the proton mass. Dust-free clouds are disrupted when D tid D sub , and therefore the largest dust-free clouds are given by M C /M ⊕ ≈ 2.4 ǫ 3 M 8 T −15.6 1500 N 3 24 , their size is R C = 5.1 × 10 13 ǫ 3/2 M 1/2 8 N 24 T −7.8 1500 cm and density n C = 1.5 × 10 10 ǫ −3/2 M −1/2 8 T 7.8 1500 cm −3 , where M ⊕ is the earth mass, ǫ = L 45 /M 8 , M 8 = M • /10 8 M ⊙ and N 24 = N H /10 24 cm −2 . For active galactic nuclei (AGNs) with M • /M ⊙ = 10 6 ∼ 10 9 and ǫ = 1, we have M C /M ⊕ ≈ 0.02 ∼ 24.0. This estimate shows that the typical properties of the captured clumps generally fulfill the photoionization condition for broad emission lines of AGNs and quasars 9 . Moreover, we realize that (M C , R C , n C ) are very sensitive to T sub , implying that properties of broad-line regions (BLR)generally depend on processes of dust production in galactic nuclei. Note that ǫ = 1 corresponds