Effects Of Sea-land Exchange On Ozone And Fine Particulate Matter At Mount Lao In Coastal Area Of North China

The distinctive local environment of China’s coastal regions is shaped by active sea-land exchange at various scales.It may change air pollutants’ physical transportation and chemical transformation processes,impacting the spatiotemporal patterns of ozone(O3)and fine particulate matter(PM2.5).Given the occurrence of atmospheric compound pollution,it is crucial to combine field observations and model simulations to comprehensively explore characteristics of O3,PM2.5,and related air pollutants at a designated site in coastal China,enabling an in-depth investigation of the impact of multiscale sea-land exchange.From April to May 2021,we conducted an atmospheric observation campaign at Mt.Lao of coastal Qingdao.During this campaign,the average concentration of O3 was 47.8± 1 2.9 ppbv with a small diurnal variation.We identified four O3 pollution episodes as the daily maximum 8-hour average concentration(MDA8)exceeding the Ambient air quality standards.The.average concentration of PM2.5 was 22.5±21.2 μg m-3,with two high-concentration processes attributed to dust.The average total volatile organic compounds(VOCs)concentration among collected samples was 23.97 ppbv,with the highest concentration occurring during O3 pollution.The concentration of water-soluble inorganic ions(WSIIs)of the PM2.5 was 14.10 μg m-3.Specifically,the average concentrations of NO3-,SO42-,and NH4+ were 4.78±5.21 μg m-3,3.14± 1.93 μg m-3 and 2.58±2.18μg m-3,respectively.Organic carbon(OC)and elemental carbon(EC)accounted for 25.18%and 6.34%of the average PM2.5 concentration during the sampling period,respectively.Utilizing the Hybrid Single Particle Lagrangian Integrated Trajectory(HYSPLIT)model,we quantitatively categorized the air masses of the observation campaign into three types:Continental,Marine,and Mixed.The probabilities of these air masses were 44.5%,35.6%,and 19.9%,respectively.The Continental type,which had higher daytime air temperature,lower relative humidity(RH),and larger diurnal variation,primarily originated from the North China Plain and inland Shandong province.Coming from the Yellow Sea and the East China Sea,the Marine air masses exhibited meteorological characteristics almost opposite to those of the Continental type.The Mixed type originated from the Shandong Peninsula and its offshore areas,and its features fell between the other two types.The zero-dimensional Observation-Based Model for investigating Atmospheric Oxidative Capacity and Photochemistry(OBM-AOCP)model was employed to assess the contribution of local photochemical reactions and regional transportation to O3 concentrations for different air masses.This analysis was also supported by the ECMWF Reanalysis V5(ERA5)reanalysis data.We found active daytime photochemical ozone production up to 9.12 ppbv h-1 under Continental air masses.The elevated nighttime O3 concentrations under Continental and Mixed air masses were attributed to sea-land breezes and O3 input from ocean regions,respectively.These findings highlighted the combination of multiscale sea-land exchange processes and local photochemical reactions exacerbating the complexity of surface O3 pollution in coastal areas.To effectively control ozone pollution,it is crucial to implement scientific reductions in precursors emissions and adopt joint prevention and control operations in larger regions.We found that NO3-was the dominant WSII,and the nitrogen oxidation ratio(NOR)was highest in PM2.5 of Continental air masses.It was primarily attributed to the promoted NO3formation by the highest NH4+ concentration.In contrast,owing to the promoted SO42formation by the highest RH,the dominant WSII of Marine air masses was SO42-,exhibiting the highest sulfur oxidation ratio(SOR).In addition,the different emission sources associated with various air masses were also responsible.The average ratio of non-sea-salt sulfate to nitrate in both Continental and Mixed air masses was lower than 1.indicating a significant contribution from mobile sources.However,the Marine air masses exhibited an average ratio of 1.98.Further analysis using potential source contribution function(PSCF)and concentration weighted trajectory(CWT)identified the high-value samples associated with air masses from shipping regions of the northwest Pacific Ocean,reflecting the contribution of sulfur compounds from marine sources.This study provided compelling evidence for the notable variations in the characteristics of O3,PM2.5,and other relevant air pollutants in coastal regions under different air masses.It underscored the importance of implementing targeted management measures in response to the local environment with multi-scale active sea-land exchange,thus scientifically controlling the compound atmospheric pollution of O3 and PM2.5 that may arise in coastal China.