摘要
基于搭设于中国气象科学研究院的多轴差分吸收光谱(MAXDOAS)站点,获得北京市2020年6月1日至2022年5月31日的二氧化氮(NO_(2))垂直廓线,底层体积分数与中国环境监测总站(CNEMC)官园站点的NO_(2)质量浓度的相关性较高(R=0.7723)。研究结果表明,北京市近地面NO_(2)最高体积分数出现在1月(17.40×10^(-9)),最低体积分数出现在4月(5.51×10^(-9))。季节特征表现为冬季(15.71×10^(-9))>秋季(15.39×10^(-9))>春季(8.52×10^(-9))>夏季(8.06×10^(-9))。不同季节NO_(2)体积分数廓线均呈e指数型,春夏季NO_(2)体积分数平均日变化呈现单峰模式,峰值出现在10:00之前,秋冬季NO_(2)体积分数平均日变化呈现双峰模式,峰值分别出现在10:00之前和15:00以后。从体积分数变化的角度并未发现北京市NO_(2)存在明显的周末效应,然而在日变化模式上却展现出显著的周末效应,主要表现为周六上午的NO_(2)峰值(16.16×10^(-9))相较于工作日和周日更大,且在时间上相较于工作日和周日存在延后,而周日下午的NO_(2)峰值显著高于工作日和周六,这可能与北京市周六集中跨城出行且在周日集中返回有关。此外,重大事件期间NO_(2)降低幅度明显大于节假日期间。重大事件期间和节假日期间底层NO_(2)平均体积分数相较于整个观测期间分别下降了29.0%和18.5%。本研究通过长期MAXDOAS观测揭示了北京市NO_(2)的垂直分布季节特征和日变化模式,发现了独特的周末效应,评估了政策性减排和节假日对NO_(2)的影响,对深入理解和有效控制NO_(2)污染具有重要意义。
Objective Nitrogen dioxide(NO_(2))not only directly affects air quality and participates in secondary chemical reactions but also influences human health.It primarily originates from industrial and vehicular emissions,as well as regional transport at higher altitudes.Therefore,surface in situ measurements alone cannot fully comprehend the highaltitude transport,vertical evolution,and atmospheric chemical processes of NO_(2).In this study,we aim to investigate the vertical distribution characteristics and temporal variations of NO_(2) in Beijing,given its status as a primary atmospheric pollutant originating from industrial activities and vehicular emissions.With Beijing’s dense population and high vehicle density,vehicular emissions constitute a major source of NO_(2).Despite improvements in air quality due to environmental policies,regional transport,especially along the southwest‒northeast corridor,remains a significant contributor to NO_(2) levels in Beijing.Traditional monitoring methods have limitations in capturing NO_(2) transport dynamics,necessitating advanced techniques such as multiaxis differential optical absorption spectroscopy(MAXDOAS).This research,based on two years of MAXDOAS observations,is designed to understand NO_(2)’s vertical distribution and its response to policy interventions and holiday effects.By providing detailed insights into NO_(2) behavior under various conditions,we support effective air quality management and policy formulation in Beijing.Methods Our study examines the spatiotemporal distribution of NO_(2) in Beijing using a MAXDOAS observation station located at the Chinese Academy of Meteorological Sciences from June 1,2020,to May 31,2022.Positioned at an elevation of 130 m,the instrument is situated 40 m above ground level with a viewing azimuth of 130°.The station is strategically placed near major NO_(2) emission sources from busy traffic areas within a 5 km radius,despite the absence of industrial emissions.The MAXDOAS instrument comprises modules for collecting sunlight scattered light and signal processing.Sunlight scattered by a rightangle prism is directed onto a single lens fiber,which transmits the light to ultraviolet and visible spectrometers covering wavelengths of 296‒408 nm and 420‒565 nm,respectively.Observations are automatically taken when the solar zenith angle(SZA)is below 92°across elevation angles ranging from 1°to 90°,with exposure times dynamically adjusted to maintain optimal signal quality.Data processed using QDOAS software undergoes leastsquares inversion to derive tropospheric slant column densities(SCDs)of NO_(2) within the 338‒370 nm wavelength range.This process includes specific parameter settings and aerosol prior profiles,alongside VLIDORT radiative transfer modeling for accurate vertical profile retrievals.Rigorous quality control criteria are applied to ensure a comprehensive analysis of NO_(2)’s spatiotemporal variations in Beijing,providing critical data support for enhancing air quality management strategies and informing policy development.Results and Discussions The bottom NO_(2) volume fraction extracted from NO_(2) vertical profiles is well correlated with the NO_(2) mass concentration measured at a CNEMC station,Guanyuan(R=0.7723,Fig.2).The study shows that the highest NO_(2) volume fraction near the ground in Beijing occurs in January(17.40×10^(-9))and the lowest in April(5.51×10^(-9),Fig.3).We find that NO_(2) volume fraction in Beijing varies in the order of winter(15.71×10^(-9))>autumn(15.39×10^(-9))>spring(8.52×10^(-9))>summer(8.06×10^(-9))for seasonal variation(Fig.4).NO_(2) profiles all show an exponential shape in different seasons.The averaged diurnal variation of NO_(2) in spring and summer exhibits a single peak pattern appearing before 10:00,and it shows a bipeak pattern in autumn and winter with peaks appearing before 10:00 and after 15:00(Fig.5).Moreover,there is not an obvious weekend effect for NO_(2) in Beijing from the perspective of concentration variations.However,it shows an obvious weekend effect from the perspective of NO_(2) diurnal variations,which mainly manifests in deferred NO_(2) peaking(16.16×10^(-9))on Saturday morning being larger than that on weekdays and Sunday and the afternoon peak on Sunday being larger than that on weekdays and Saturday.This may be related to the travel crosscities on Saturday and return on Sunday(Fig.7).In addition,we also reveal that the reduction of NO_(2) in Beijing during major events is significantly greater than that during holidays.The average volume fraction of surface NO_(2) during major events and holidays decreases by 29.0%and 18.5%,respectively,compared with the whole observation period(Fig.8).Conclusions During the period from June 1,2020,to May 31,2022,we conduct continuous MAXDOAS NO_(2) remote sensing observations in Beijing.Using a leastsquares algorithm,we derive NO_(2) slant column densities(SCDs)from various elevation angles,enabling us to construct NO_(2) vertical profiles for the entire observation period using an optimal estimation method.The correlation coefficient between the derived nearsurface NO_(2) volume fractions and mass concentrations from CNEMC stations reaches 0.7723,which indicates strong agreement.Key findings include monthly variations in nearsurface NO_(2) volume fractions,with peak levels observed during winter(17.40×10^(-9))and lowest levels in April(5.51×10^(-9)).NO_(2) vertical distribution exhibits a seasonal pattern,with higher volume fractions observed in winter and autumn compared to spring and summer.Daily variations in NO_(2) volume fraction show distinct patterns depending on the season:single peaks before 10:00 in spring and summer,and double peaks before 10:00 and after 15:00 in autumn and winter.Notably,NO_(2) volume fractions decline more rapidly after 10:00 in spring and summer due to increased boundary layer heights and solar radiation intensity.Weekend effects are also observed,with NO_(2) volume fractions decreasing by 1.5%on Saturdays and 7.0%on Sundays compared to weekdays.Weekday,Saturday,and Sunday variations show doublepeak patterns,with peaks occurring before 08:00 and after 16:00.Saturdays exhibit the highest peak volume fraction and a delayed peak compared to weekdays and Sundays.Analysis during holidays and major events reveals decreased NO_(2) volume fractions of 29.0%and 18.5%,respectively,compared to the overall period.Both periods show doublepeak patterns,with peaks before 09:00 and after 16:00,although volume fractions are lower during major events compared to holidays.These findings emphasize the importance of longterm MAXDOAS NO_(2) vertical observations in understanding its influence on the atmospheric environment and supporting NO_(2) prevention and control efforts in Beijing.
作者
陈健
邢成志
林继楠
刘诚
Chen Jian;Xing Chengzhi;Lin Jinan;Liu Cheng(Department of Precision Machinery and Precision Instrumentation,University of Science and Technology of China,Hefei 230026,Anhui,China;Key Laboratory of Environmental Optics&Technology,Chinese Academy of Sciences,Anhui Institute of Optics and Fine Mechanics,Hefei Institutes of Physical Science,Chinese Academy of Sciences,Hefei 230031,Anhui,China)
出处
《光学学报》
CSCD
北大核心
2024年第24期60-71,共12页
Acta Optica Sinica
基金
国家自然科学基金(U21A2027)
国家重点研发计划(2019YFC0214702)
安徽省自然科学基金(2108085QD180)。
关键词
光谱学
二氧化氮
垂直分布
季节变化
周末效应
冬奥会
spectroscopy
nitrogen dioxide
vertical distribution
seasonal variation
weekend effect
Winter Olympics
