The less improvement of ambient visibility suspects the government’s efforts on alleviating PM_2.5 pollution. The COVID-19 lockdown reduced PM_2.5 and increased visibility in Wuhan. Compared to pre-lockdown period, the PM_2.5 concentration decreased by 39.0 μg m⁻³, dominated by NH₄NO₃ mass reduction (24.8 μg m⁻³) during lockdown period. The PM_2.5 threshold corresponding to visibility of 10 km (PTV₁₀) varied in 54–175 μg m⁻³ and an hourly PM_2.5 of 54 μg m⁻³ was recommended to prevent haze occurrence. The lockdown measures elevated PTV₁₀ by 9–58 μg m⁻³ as the decreases in PM_2.5 mass scattering efficiency and optical hygroscopicity. The visibility increased by 107%, resulted from NH₄NO₃ extinction reduction. The NH₄NO₃ mass reduction weakened its mutual promotion with aerosol water and increased PM_2.5 deliquescence humidity. Controlling TNO₃ (HNO₃ + NO₃⁻) was more effective to reduce PM_2.5 and improve visibility than NH_x (NH₃ + NH₄⁺) unless the NH_x reduction exceeded 11.7–17.5 μg m⁻³.

环境能见度的改善较少怀疑政府在减轻 PM _2.5污染方面的努力。COVID-19 封锁降低了 PM _2.5并提高了武汉的能见度。与封锁前相比，PM _2.5浓度降低了 39.0 μg m ^-3，主要是在封锁期间NH ₄ NO ₃质量减少（24.8 μg m ^-3）。对应于 10 公里能见度 (PTV ₁₀ )的 PM _2.5阈值在 54–175 μg m ^{-3 之间}变化，每小时 PM _2.5为 54 μg m ^-3建议防止雾霾发生。随着 PM _2.5质量散射效率和光学吸湿性的降低，锁定措施使 PTV ₁₀升高了 9–58 μg m ^-3。由于NH ₄ NO ₃消光减少，能见度增加了107% 。NH ₄ NO ₃质量减少减弱了其与气溶胶水的相互促进作用，增加了PM _2.5潮解湿度。控制TNO ₃（HNO ₃  + NO ₃ ^- ）为更有效地降低PM _2.5，提高能见度比NH _X（NH ₃ + NH ₄ ⁺ ) 除非 NH _x减少超过 11.7–17.5 μg m ^-3。