Rate coefficients for three daytime atmospheric reactions of UV photolysis (Z)-3-hexenal (3HA)-photolysis (J(1)), reaction with OH radicals (k(2)), and reaction with ozone (k(3))-were measured at 760 Torr and 298 K using a 6 m(3) photochemical reaction chamber. The UV absorption cross sections (sigma(3HA)(lambda)) were obtained in the wavelength range 240-350 nm. The photodissociation rate of 3HA relative to that of NO2 was measured by a solar simulator at 760 Torr and was determined to be J(1)/J(NO2) = (4.7 +/- 04) x 10(-3). Using the obtained sigma(3HA)(lambda) and J(1)/J(NO2) the effective photodissociation quantum yield was calculated to be Phi(3HA) = 0.25 +/- 0.06. The rate coefficient for the reaction with OH radicals Was measured by the relative rate method with three reference compounds and was determined to be k(2) = (6.9 +/- 0.9) x 10(-11) cm(3) molecule(-1) s(-1). The rate coefficient for the reaction with ozone was measured by an absolute method and was determined to be k(3) = (3.5 +/- 0.2) X 10(-17) cm(3) molecule(-1) s(-1). Using the obtained rate coefficients, the daytime atmospheric lifetime of 3HA was estimated.