Interpretation of NO<sub>3</sub>–N<sub>2</sub>O<sub>5</sub> observation via steady state in high-aerosol air mass: the impact of equilibrium coefficient in ambient conditions

Abstract. Steady-state approximation for interpreting NO3 and N2O5 has large uncertainty under complicated ambient conditions could even produce incorrect results unconsciously. To provide an assessment solution to the dilemma, we formulate datasets based on in situ observations reassess applicability of method. In most steady-state cases, find a prominent discrepancy between Keq (equilibrium coefficient reversible reactions N2O5) correspondingly simulated [N2O5]/[NO2]×[NO3], especially high-aerosol winter. This gap reveals that accuracy critical impact analysis polluted regions. addition, γ (N2O5) derived by fit depends closely reactivity (kNO3) N2O5(kN2O5). Based complete set simulations, air mass kNO3 less than 0.01 s−1 with high aerosol temperature higher 10 ∘C is suggested be best suited NO3–N2O5 chemistry. Instead confirming validity steady state numerical modeling every case, this work directly provides appropriate concentration ranges accurate approximation, implications choosing methods interpret nighttime chemistry mass.