Spectral dependence on the correction factor of erythemal UV for cloud,aerosol, total ozone,and surface properties: A modeling study

Radiative transfer model simulations were used to investigate the erythemal ultraviolet(EUV) correction factors by separating the UV-A and UV-B spectral ranges. The correction factor was defined as the ratio of EUV caused by changing the amounts and characteristics of the extinction and scattering materials. The EUV correction factors(CFEUV) for UV-A[CFEUV(A)] and UV-B [CFEUV(B)] were affected by changes in the total ozone, optical depths of aerosol and cloud, and the solar zenith angle. The differences between CFEUV(A) and CFEUV(B) were also estimated as a function of solar zenith angle, the optical depths of aerosol and cloud, and total ozone. The differences between CFEUV(A) and CFEUV(B) ranged from-5.0% to 25.0% for aerosols, and from-9.5% to 2.0% for clouds in all simulations for different solar zenith angles and optical depths of aerosol and cloud. The rate of decline of CFEUV per unit optical depth between UV-A and UV-B differed by up to 20% for the same aerosol and cloud conditions. For total ozone, the variation in CFEUV(A) was negligible compared with that in CFEUV(B) because of the effective spectral range of the ozone absorption band. In addition, the sensitivity of the CFEUVs due to changes in surface conditions(i.e., surface albedo and surface altitude) was also estimated by using the model in this study. For changes in surface albedo, the sensitivity of the CFEUVs was 2.9%–4.1% per 0.1 albedo change,depending on the amount of aerosols or clouds. For changes in surface altitude, the sensitivity of CFEUV(B) was twice that of CFEUV(A), because the Rayleigh optical depth increased significantly at shorter wavelengths.     

我国对流层大气臭氧的数值模拟

本文建立了一个用于对流层大气臭氧模拟的三维欧拉模式,针对影响臭氧光化学转化的各种因素及我国城市光化学污染的特点,模式中简化了光化学项的计算。根据实际观测资料,提出了模拟云雾对臭氧影响的参数化方法,并确定了云雾作用系数,通过模式的数值模拟,得出了我国对流层大气臭氧,特别是近地面层大气臭氧的分布状况、我国城市光化学污染的分布特征以及它们的季节变化规律.     

Kinetic limitations on cloud droplet formation and impact on cloud albedo

Under certain conditions mass transfer limitations on the growth of cloud condensation nuclei (CCN) may have a significant impact on the number of droplets that can form in a cloud. The assumption that particles remain in equilibrium until activated may therefore not always be appropriate for aerosol populations existing in the atmosphere. This work identifies three mechanisms that lead to kinetic limitations, the effect of which on activated cloud droplet number and cloud albedo is assessed using a one‐dimensional cloud parcel model with detailed microphysics for a variety of aerosol size distributions and updraft velocities. In assessing the effect of kinetic limitations, we have assumed as cloud droplets not only those that are strictly activated (as dictated by classical Köhler theory), but also unactivated drops large enough to have an impact on cloud optical properties. Aerosol number concentration is found to be the key parameter that controls the significance of kinetic effects. Simulations indicate that the equilibrium assumption leads to an overprediction of droplet number by less than 10% for marine aerosol; this overprediction can exceed 40% for urban type aerosol. Overall, the effect of kinetic limitations on cloud albedo can be considered important when equilibrium activation theory consistently overpredicts droplet number by more than 10%. The maximum change in cloud albedo as a result of kinetic limitations is less than 0.005 for cases such as marine aerosol; however albedo differences can exceed 0.1 under more polluted conditions. Kinetic limitations are thus not expected to be climatically significant on a global scale, but can regionally have a large impact on cloud albedo.     

Surface albedo at a tower site in Lake Ontario

Measurements of incoming global, diffuse and reflected radiation at a tower site in Lake Ontario are used to evaluate components of surface albedo. Albedo for diffuse radiation lies between 0.074 and 0.082 and a coefficient for backscatter from sub-surface water layers shows little deviation from a mean of 0.017. Direct beam albedo for a calm surface follows the Fresnel law. Waves increase direct-beam albedo particularly at higher solar zenith angles. A pronounced dependence of albedo upon zenith angle for clear skies decreases with increasing cloud amount and becomes undetectable in overcast conditions. On a daily basis, albedo ranged between 0.07 in early July to 0.11 in mid-November. Day-to-day scatter is within ±1% of the mean seasonal trend.     

Urban Surface Modification as a Potential Ozone Air-quality Improvement Strategy in California: A Mesoscale Modelling Study

Two of several surface modification (heat-island reduction) strategies, increased surface albedo and urban reforestation, are evaluated via mesoscale meteorological and photochemical modelling of regulatory episodes in central and southern California. The simulations suggest that these strategies can have beneficial impacts on air quality, with increased albedo being relatively more effective than urban reforestation. The simulations also show that air quality indices, such as regional 1-h peaks, area peaks, 8-h relative reduction factors, 24-h averages, etc., improve for both central and southern California and that for the range of strategies evaluated here, the improvements in air quality can be significant. The simulations of southern California suggest that there may be a threshold beyond which further surface modifications tend to produce smaller net improvements in ozone air quality.     

地面臭氧的变化规律和计算方法的初步研究Ⅱ.可见光波段

通过对广州鼎湖山近地面O3、NOx、太阳辐射,气象参数等项目的观测和理论分析,研究了地面O3与NOx等微量气体及太阳可见光辐射的变化规律,详细讨论了可见光波段、不同天气条件地面O3与NOx、光化学反应、气溶胶、可见光辐射等之间复杂的关系.提出以光能量传输与守恒的观点来考虑大气中与可见光辐射有关的主要过程,并以此来研究大气光化学过程中所遵循的能量规律,建立了一个简单、实用、省时的统计模式,用于计算地面O3浓度.结果表明:不同情况下,计算值与观测值吻合得均比较一致.     

地面臭氧的变化规律和计算方法的初步研究Ⅰ.紫外波段

通过对广州鼎湖山近地面O3、NOx、太阳辐射、气象参数等项目的观测和理论分析,研究了地面O3与NOx等微量气体及太阳辐射的变化规律,详细讨论了紫外波段、不同天气条件地面O3与NOx,光化学反应、气溶胶、光化辐射等之间复杂的关系.用光能量传输与守恒的观点来考虑大气中与紫外辐射有关的主要过程,并以此来研究大气光化学过程中所遵循的能量规律,建立了一个简单、实用、省时的统计模式,用于计算地面O3浓度.结果表明,不同情况下计算值与观测值均吻合较好.     

The effect of ozone photochemistry on atmospheric and surface temperature changes due to increased CO2, N2O,CH4 and volcanic aerosols in the atmosphere

Abstract

A coupled 1‐D radiative‐convective and photochemical diffusion model is used to study the influence of ozone photochemistry on changes in the vertical temperature structure and surface climate resulting from the doubling of atmospheric CO₂, N₂O, CH₄ and increased stratospheric aerosols owing to the El Chichón volcanic eruption. It is found when CO₂ alone is doubled, that the total ozone column increases by nearly 6% and the resulting increase in the solar heating contributes a smaller temperature decrease in the stratosphere (up to 4 K near the stratopause level). When the concentration of CO₂, N₂O and CH₄ are simultaneously doubled, the total ozone column amount increases by only 2.5% resulting in a reduced temperature recovery in the stratosphere. Additional results concerning the effect of the interaction of ozone photochemistry with the stratospheric aerosol cloud produced by the El Chichón eruption show that it leads to a reduction in stratospheric ozone, which in turn has the effect of increasing the cooling at the surface and above the cloud centre while causing a slight warming below in the lower stratosphere.     

夏季硫酸盐和黑碳气溶胶对中国云特性的影响

利用WRF-Chem（Weather Research and Forecasting model coupled with Chemistry）模式研究2006年8月1日—9月1日中国区域硫酸盐和黑碳气溶胶对云特性的影响。模式验证利用了卫星和地面观测的气象要素、化学物质浓度、气溶胶光学特性和云微物理特性。模式性能评估表明该模式能较好地抓住气象要素（温度、降水、相对湿度和风速）的量级和空间分布特征。通过与地面观测和MODIS卫星数据对比发现,尽管模式模拟还存在偏差,但还是能较好模拟出气溶胶物种的地表浓度、气溶胶光学厚度（AOD）、云光学厚度（COD）、云量（CLDF）、云顶云滴有效半径（CER）和云水路径（LWP）。通过两个敏感性试验（分别增加二氧化硫和黑碳排放量至控制试验排放的3倍）与控制试验的对比发现硫酸盐比黑碳更易成为云凝结核,在中国东部云顶云滴数浓度和其它云特性参数对二氧化硫排放增加的响应均从北向南呈递增,这与地面湿度分布有关。云滴有效半径对硫酸盐气溶胶的响应符合气溶胶第一间接效应的定义,即硫酸盐气溶胶增多,云滴数浓度增加,云滴有效半径减少,但是对黑碳气溶胶的响应在各区域不尽相同。还发现黑碳对云量的影响远大于硫酸盐,主要原因是由于黑碳气溶胶直接辐射效应（对太阳光的吸收）导致的云的“燃烧”作用。      

Turbulence Effects on Precipitation and Cloud Radiative Properties in Shallow Cumulus: an Investigation Using the WRF-LES Model Coupled with Bin Microphysics

Using the large-eddy simulation version of the Weather Research and Forecasting (WRF) model coupled with a detailed bin microphysics scheme, the effects of turbulence-induced collision enhancement (TICE) on precipitation and cloud radiative properties in shallow cumulus are investigated. Similar to previous studies, the enhanced droplet collision results in an increase in rainwater content and surface precipitation amount. However, under low aerosol number concentration, the relative frequency of large surface precipitation amount is decreased mainly due to the decreased condensation amount. Due to TICE, the mean drop size increases and the drop number concentration decreases, which results in a decrease in evaporation and hence increasing cloud fraction. However, these changes induce a decrease in cloud optical thickness which largely offsets the increased cloud fraction when the domain-averaged albedo is calculated. Similarly, a decrease in cloud top height caused by the decreased in-cloud vertical velocity largely offsets the increased cloud fraction when the domain-averaged outgoing longwave radiation is calculated. Therefore, the effects of TICE on cloud radiative properties in shallow cumulus do not appear prominently. In addition, TICE results in a decrease in the shear production of turbulent kinetic energy, which indicates that TICE acts to produce a negative feedback.     

A comparison of photolysis rate parameters estimated from measured and simulated actinic flux for wintertime conditions at Storm Peak Laboratory,Colorado

Photolysis rate parameters depend upon solar actinic flux and chemical species dependent quantum yields and cross sections. Spectrally resolved measurements of actinic flux should be preferred over flux derived from models for the analysis of field observations. Actinic flux can be difficult to derive from the irradiance measurements of flat-plate radiometers. It is also difficult to estimate from models due to uncertainties in the ozone column, aerosol concentrations and distributions, cloud cover, optical depth and surface albedo. A series of actinic flux measurements were performed at Storm Peak Laboratory (3,210 m above sea level), Colorado, United States with spectroradiometers during the wintertime (January 07–10, 2004). The site is relatively remote with a clean atmosphere and during the wintertime the ground is generally covered by fresh snow with a high albedo. The actinic flux measurements were used to estimate the photolysis rate parameters of ozone, nitrogen dioxide and formaldehyde. The measured actinic flux and the photolysis rate parameters derived from the flux were compared to calculations using the Tropospheric Ultraviolet-Visible Model (TUV), version 4.2 (Madronich and Flocke, 1998). The TUV modeled actinic flux, the measured flux and the photolysis rate parameters derived from them had similar temporal patterns. However there were significant differences in their magnitude due to uncertainties in the data available to initialize the TUV model and the calibration of the spectroradiometer.     

The ozone,aerosol depletion and condensation nuclei events in the stratosphere

Recently, the depletion in ozone and aerosol extinctions inside Antarctic Spring westerly vortex and condensa-tion nuclei enhancement events in the mid latitudes stratosphere were related to downward transport of aerosols by subsidence and sedimentation. However, the problems associated with such hypothesis would keep a constraint on photochemical theories on ozone hole and stratospheric condensation nuclei (CN) events. Alternately, the gross fea-tures of aerosol hole are better explicable assuming a reversed residual circulation. This opens a path for combined operation on ozone by both photochemistry and dynamics in the same space domain.Independently, we relate the CN events to the growth and transport of negative ion complexes above the Peak of Junge Layer (PJL) without invoking photochemistry in order to be consistant with the observed interhemispheric dif-ferences in the planetary wave activity and CN concentration.     

Reconstruction of erythemal UV irradiance and dose at Hohenpeissenberg (1968–2001) considering trends of total ozone, cloudiness and turbidity

Summary Erythemal ultraviolet (UV) doses reaching the earths surface depend in a complex manner on the amount of total ozone, cloud cover, cloud type and the structure of the cloud field. A statistical model was developed allowing the reconstruction of UV from measured total ozone and a cloud modification factor (CMF) for the GAW site Hohenpeissenberg, Germany (48°N, 11°E). CMF is derived from solar global radiation G, normalized against a Rayleigh scattering atmosphere. By this way the complex influence of the cloud field is accounted for by introduction of a measured parameter, exposed also to this complex field. The statistical relations are derived from the period 1990–1998 where UV measurements and relevant meteorological parameters are available. With these relations daily UV doses could be reconstructed back to 1968. Tests show that the model works remarkably well even for time scales of a minute except for situations with high albedo. The comparison of measured and calculated UV irradiances shows that the model explains 97% of the variance for solar elevations above 18° on average over the period 1968–2001. The reconstruction back to 1968 indicates that maximum UV irradiances (clear days) have increased due to long-term ozone decline. Clouds show seasonally depending long-term changes, especially an increase of cirrus. Consequently the UV doses have increased less or even decreased in some months in comparison to the changes expected from the ozone decline alone. In May to August total cloud frequency and cloud cover have decreased. Therefore, the average UV doses have increased much more than can be explained by the ozone decline alone. It is also shown that the optical thickness of cirrus clouds has increased since 1953. The higher frequency of cirrus is caused in part by more frequent contrails. Besides that an observed long-term rise and cooling of the tropopause favors an easier cirrus formation. However, whether climate change and an intensification of the water cycle is responsible for the cirrus trends has not been investigated in detail.     

A meteorological analysis of ozone episodes using HYSPLIT model and surface data

Ozone episodes (> 100 ppbv) were observed frequently in Jinan, an urban site located between the highly polluted Yangtze Delta and Beijing–Tianjin region in East China. In this study, the ozone episodes observed in 2004 were analysed using the Hybrid Single-particle Lagrangian Integrated Trajectory (HYSPLIT) model and surface meteorological data, as well as Air Pollution Index (API). The meteorological conditions of episode days and non-episode days were compared and examined, and categorization of 6 groups of backward trajectories was performed. The results show that, most episodes were caused by local photochemical production (e.g., induced by sufficient sunshine duration and high temperature) and pollutant accumulation (e.g., induced by little rainfall and low wind speed), and transport of pollutants from the highly polluted regions could significantly influence the air quality at the site, especially from Yangtze Delta region. In addition, three typical ozone episodes were analysed using HYSPLIT model to infer any long-distance transport and surface meteorological data to infer the local ozone production potential. At last, the functions and inadequacies about the usage of HYSPLIT model combined with surface meteorological data for the analysis of photochemical pollution were discussed.     

大城市气溶胶对光化辐射通量及臭氧的影响研究(Ⅱ)——数值试验分析

城市化已引起大量痕量气态污染物、气溶胶以及臭氧前体物的人为排放,从而引起区域大气化学循环的扰动变化。在分析国内外研究现状与观测实例的基础上,进一步用辐射模式与化学模式研究了气溶胶对到达地面的光化辐射通量以及臭氧形成的影响,表明气溶胶可显著减小到达地面的光化学辐射通量,减缓光化学反应进程,并进一步抑制臭氧的形成;在目前广州等大城市的污染过程中,高浓度的气溶胶可造成光化学辐射通量衰减高达70%~80%,紫外线的衰减比可见光更明显,在可见光波段随波长增大衰减幅度减小,气溶胶层的存在对短波长激发的光化学过程的影响更加显著。分析说明城市污染大气中光化学反应的生成物与反应物之间存在自抑制过程,在目前的城市群复合污染情况下,气溶胶与臭氧之间的非线性相互作用值得关注。     

惠州市臭氧污染特征及其与气象条件关系研究

利用广东省惠州市区2013—2016年逐日、逐时的环境和气象资料, 研究了珠江三角洲(简称“珠三角”)东侧惠州市臭氧污染特征及其与气象条件关系。结果表明:惠州市臭氧污染具有明显的月和季节变化特征, 10月臭氧平均浓度最高, 臭氧超标日和污染日主要出现在7—10月。惠州市臭氧浓度日变化呈单峰变化, 06—08时最低, 最大值出现在午后14—15时。臭氧浓度变化和气象条件关系密切, 低浓度臭氧大多出现在气温较低、相对湿度和风速较大、云量较多伴有降水、日照时数较小的天气, 臭氧浓度超标多出现在气温较高、相对湿度和风速较小、云量较少一般无降水、日照充足的天气。惠州市臭氧超标主要出现在地面和低空偏西风下, 这可能与惠州市处于珠三角城市群下风向的区域污染输送有关。      

沙尘气溶胶对云和降水影响的模拟研究

采用二维分档云模式,对比背景大气气溶胶分布,讨论了扬沙和沙尘暴天气条件下矿物气溶胶对云微物理结构、光学特性以及降水形成的影响.结果表明:扬沙和沙尘暴天气增加大气中大核和巨核的浓度,促进云中水汽的活化,使降水提前出现,暖云和冷云降水量均大幅增加,但可忽略巨核增加对云光学厚度和反照率的作用;当矿物沙尘粒子同时作为有效的云凝结核和冰核参与云的发展时,冰核浓度增加使水成物有效半径减小,抑制了暖云和冷云降水,云内存留的大量冰晶增强云的光学厚度和反照率.     

基于TUV模式的银川光化辐射通量特征及其影响因子

利用TUV模式计算分析了银川光化辐射通量变化特征,探讨了云、气溶胶、臭氧柱浓度、NO_(2)柱浓度等因子对银川光化辐射通量的影响。结果表明:2019年7—9月银川月平均光化辐射通量分别为6.5E+16光子数·cm^(-2)·s^(-1)、5.6E+16光子数·cm^(-2)·s^(-1)和4.7E+16光子数·cm^(-2)·s^(-1),日最大值出现在13:00;波长小于325 nm时,光化辐射通量随波长增加缓慢上升,波长在325—480 nm之间时,光化辐射通量迅速升高,波长大于480 nm时,光化辐射通量随波长增加变化较小,此特征在中午前后较早晚表现更明显;云光学厚度和气溶胶光学厚度对光化辐射通量的衰减作用具有明显的“U”型日变化特征,比较而言,气溶胶光学厚度对光化辐射通量衰减作用的“U”型波形更为宽广;光化辐射通量衰减率对较低的云光学厚度的变化更敏感;光化辐射通量随气溶胶光学厚度增加而减小的变率要比随云光学厚度增加而减小的变率小;光化辐射通量对单次散射反照比大于0.6的强散射性气溶胶的变化更敏感,且气溶胶光学厚度越大,此特性整体表现越明显;波长指数对光化辐射通量的影响相对较小。     

天津地区近40年日照时数变化特征及其影响因素

对天津市区、西青、蓟县、塘沽4个站1961~2003年日照时数以及对日照有影响的云量、水汽压和地面能见度等资料的进行了统计分析。结果表明:天津地区日照时数呈明显的下降趋势,1961~2003年4站气候变化率分别是为每10年-177.3-、165.2-、174.1-、145.6 h。与60年代相比,90年代4站的年日照时数分别减少了425.1、403.4、486.03、77.5 h,相当于市区每日的日照时数减少了1.2 h、西青1.1 h、蓟县1.3 h、塘沽1.0 h。40年来云量和水汽压的变化不大,而地面能见度呈下降趋势。能见度下降可能主要是对流层大气气溶胶含量上升的结果,这是造成天津地区日照时数减少的主要原因。     

Albedo enhancement over land to counteract global warming: impacts on hydrological cycle

A recent modelling study has shown that precipitation and runoff over land would increase when the reflectivity of marine clouds is increased to counter global warming. This implies that large scale albedo enhancement over land could lead to a decrease in runoff over land. In this study, we perform simulations using NCAR CAM3.1 that have implications for Solar Radiation Management geoengineering schemes that increase the albedo over land. We find that an increase in reflectivity over land that mitigates the global mean warming from a doubling of CO₂ leads to a large residual warming in the southern hemisphere and cooling in the northern hemisphere since most of the land is located in northern hemisphere. Precipitation and runoff over land decrease by 13.4 and 22.3%, respectively, because of a large residual sinking motion over land triggered by albedo enhancement over land. Soil water content also declines when albedo over land is enhanced. The simulated magnitude of hydrological changes over land are much larger when compared to changes over oceans in the recent marine cloud albedo enhancement study since the radiative forcing over land needed (?8.2?W?m^?2) to counter global mean radiative forcing from a doubling of CO₂ (3.3?W?m^?2) is approximately twice the forcing needed over the oceans (?4.2?W?m^?2). Our results imply that albedo enhancement over oceans produce climates closer to the unperturbed climate state than do albedo changes on land when the consequences on land hydrology are considered. Our study also has important implications for any intentional or unintentional large scale changes in land surface albedo such as deforestation/afforestation/reforestation, air pollution, and desert and urban albedo modification.