Using a fast-flow-discharge technique, absolute rate coefficients for the gas-phase reactions of the NO₃ radical with a series of branched aldehydes (2-methylpropanal, 2,2-dimethylpropanal, 2-methylbutanal and 3-methylbutanal) have been determined. The experiments were carried out monitoring the NO₃ radical by laser induced fluorescence (LIF). The temperature dependence of the reaction was studied in the range between 298 and 433 K. The proposed Arrhenius expressions, are respectively:

k ₁ = (1.0 ± 0.5) × 10⁻¹⁰exp[−(2598 ± 384)/T]/cm³ molecule⁻¹ s⁻¹,

k ₂ = (2.7 ± 1.2) × 10⁻¹¹exp[−(2063 ± 356)/T]/cm³ molecule⁻¹ s⁻¹,

k ₃ = (5.5 ± 3.1) × 10⁻¹¹exp[−(2296 ± 555)/T]/cm³ molecule⁻¹ s⁻¹,

k ₄ = (3.7 ± 1.4) × 10⁻¹¹exp[−(2184 ± 230)/T]/cm³ molecule⁻¹ s⁻¹.

Tropospheric lifetimes for these aldehydes have been calculated at night and during the daytime for typical NO₃ and OH average concentrations.