Ozone pollution characteristics and sensitivity analysis using an observation-based model in Nanjing,Yangtze River Delta Region of China

Ground-level ozone(O3)has become a critical pollutant impeding air quality improvement in Yangtze River Delta region of China.In this study,we present O3 pollution characteristics based on one-year online measurements during 2016 at an urban site in Nanjing,Jiangsu Province.Then,the sensitivity of O3 to its precursors during 2 O3 pollution episodes in August was analyzed using a box model based on observation(OBM).The relative incremental reactivity(RIR)of hydrocarbons was larger than other precursors,suggesting that hydrocarbons played the dominant role in O3 formation.The RIR values for NOX ranged from–0.41%/%to 0.19%/%.The O3 sensitivity was also analyzed based on relationship of simulated O3 production rates with reductions of VOC and NOX derived from scenario analyses.Simulation results illustrate that O3 formation was between VOCs-limited and transition regime.Xylenes and light alkenes were found to be key species in O3 formation according to RIR values,and their sources were determined using the Positive Matrix Factorization(PMF)model.Paints and solvent use was the largest contributor to xylenes(54%),while petrochemical industry was the most important source to propene(82%).Discussions on VOCs and NOX reduction schemes suggest that the 5%O3 control goal can be achieved by reducing VOCs by 20%.To obtain 10%O3 control goal,VOCs need to be reduced by 30%with VOCs/NOX larger than 3:1.

Photooxidation of arsenic(Ⅲ) to arsenic(Ⅴ) on the surface of kaolinite clay

As one of the most toxic heavy metals, the oxidation of inorganic arsenic has drawn great attention among environmental scientists. However, little has been reported on the solar photochemical behavior of arsenic species on top-soil. In the present work, the influencing factors（p H, relative humidity（RH）, humic acid（HA）, trisodium citrate, and additional iron ions） and the contributions of reactive oxygen species（ROS, mainly HO^- and HO2^-/O2^-） to photooxidation of As（Ⅲ） to As（Ⅴ） on kaolinite surfaces under UV irradiation（λ = 365 nm）were investigated. Results showed that lower p H facilitated photooxidation, and the photooxidation efficiency increased with the increase of RH and trisodium citrate.Promotion or inhibition of As（Ⅲ） photooxidation by HA was observed at low or high dosages, respectively. Additional iron ions greatly promoted the photooxidation, but excessive amounts of Fe^2＋competed with As（Ⅲ） for oxidation by ROS. Experiments on scavengers indicated that the HOUradical was the predominant oxidant in this system.Experiments on actual soil surfaces proved the occurrence of As（Ⅲ） photooxidation in real topsoil. This work demonstrates that the photooxidation process of As（Ⅲ） on the soil surface should be taken into account when studying the fate of arsenic in natural soil newly polluted with acidic wastewater containing As（Ⅲ）.