[Observation Analysis on the Characteristics of Meteorological Elements and Pollutants During a Continuous Fog and Haze Episode in Spring in Jiaxing City]

A continuous fog and haze episode occurred on 17-20 May, 2015 in Jiaxing. Trace gases (O₃, CO, SO₂ and NO₂), PM₁₀, PM_2.5, aerosol number concentration in the range of 10 nm-10 μm, meteorological elements, and radiosonde data from the 17st to the 22st of May were used to analyze the formation mechanism and pollutant characteristics during this episode. The results showed that subtropical high pressure lifted northward, a field pressure was dominant over Jiaxing leading to a weak ground wind speed, and a strong inversion layer occurred, this supplied moisture, power and thermal conditions for the occurrence and maintenance of the event. The episode included one precipitation process and two fog processes (rainy fog and radiation-advection fog). During the fog and haze process, the concentrations of NO₂, CO, PM₁₀ and PM_2.5 were high and the levels of SO₂ and O₃ were low. Strong precipitation had greater scavenge effects on PM₁₀, PM_2.5 and SO₂, while weak precipitation aggravated the pollution degree. The PM concentrations increased continuously during the rainy fog process, while it decreased firstly and then increased during the radiation-advection fog process. The spectral distributions of aerosol number concentration were unimodal and differed significantly under different types of weather conditions. The peaks of number concentration were located at 20-30 nm, 100 nm, 30-60 nm, 120 nm, 90 nm under clean, precipitation, fog and haze, rainy fog, radiation-advection fog conditions, respectively. The spectra of surface area concentration were trimodal under clean, precipitation, fog and haze, rainy fog conditions, and had four peaks under radiation-advection fog condition.