Relative optical mass functions for air, water vapour, ozone and nitrogen dioxide in atmospheric models presenting different latitudinal and seasonal conditions

Summary A study of the dependence features of the relative optical mass functions for air, water vapour, ozone and nitrogen dioxide on the apparent solar zenith angle was performed by calculating these optical parameters by means of the well-known computer code LOWTRAN 7 at several values of and for nine atmospheric models characterized by different latitudes and seasons. Moreover, other investigations were performed on the dependence features of (i) the relative optical air mass on the thermal characteristics of the low troposphere, (ii) the relative optical water vapour mass on the vertical distribution characteristics of absolute humidity in the troposphere, and (iii) the relative optical mass function for ozone and nitrogen dioxide on the shape characteristics of the vertical profiles of the two gaseous concentrations and the concentration peak altitudes. The results are compared with the values given by the two simple formulas proposed by Kasten (1966) for air and water vapour and the formulas defined by Young (1969) and Staehelin et al. (1995) for ozone and nitrogen dioxide. From this comparison, a wide set of correction factors were obtained which can be conveniently used in the analysis of multispectral sun-radiometric measurements for calculating, with a very high precision, the values of the four optical mass functions at all the angles in the 0° to 87° range, corresponding to the various latitudinal and seasonal conditions described by the nine atmospheric models.With 9 Figures     

Tropospheric ozone and oxides of nitrogen over the north-western Pacific in summer

In summer, atmospheric ozone was measured from an aircraft platform simultaneously with nitric oxide (NO), oxides of nitrogen (NO _y ), and water vapor over the Pacific Ocean in east Asia from 34° N to 19° N along the longitude of 138±3°E. NO _y was measured with the aid of a ferrous sulfate converter. The altitude covered was from 0.5 to 5 km. A good correlation in the smoothed meridional distributions between ozone and NO _y was seen. In particular, north of 25° N, ozone and NO _y mixing ratios were considerably higher than those observed in tropical marine air south of 25° N. NO _y and O₃ reached a minimum of 50 pptv and 4 ppbv respectively in the boundary layer at a latitude of 20° N. The NO concentration between 2 and 5 km at the same latitude was 30 pptv. The profiles of ozone and water vapor mixing ratios were highly anti-correlated between 25° N and 20° N. In contrast, it was much poorer at the latitude of 33° N, suggesting a net photochemical production of ozone there.     

Vertical distribution of dimethylsulfide,sulfur dioxide,aerosol ions,and radon over the Northeast Pacific Ocean

Dimethylsulfide (DMS), sulfur dioxide (SO₂), methanesulfonate (MSA), nonsea-salt sulfate (nss-SO₄ ^2–), sodium (Na⁺), ammonium (NH₄ ⁺), and nitrate (NO₃ ^–) were determined in samples collected by aircraft over the open ocean in postfrontal maritime air masses off the northwest coast of the United States (3–12 May 1985). Measurements of radon daughter concentrations and isentropic trajectory calculations suggested that these air masses had been over the Pacific for 4–8 days since leaving the Asian continent. The DMS and MSA profiles showed very similar structures, with typical concentrations of 0.3–1.2 and 0.25–0.31 nmol m^–3 (STP) respectively in the mixed layer, decreasing to 0.01–0.12 and 0.03–0.13 nmol m^–3 (STP) at 3.6 km. These low atmospheric DMS concentrations are consistent with low levels of DMS measured in the surface waters of the northeastern Pacific during the study period.The atmospheric SO₂ concentrations always increased with altitude from <0.16–0.25 to 0.44–1.31 nmol m^–3 (STP). The nonsea-salt sulfate (ns-SO₄ ^2–) concentrations decreased with altitude in the boundary layer and increased again in the free troposphere. These data suggest that, at least under the conditions prevailing during our flights, the production of SO₂ and nss-SO₄ ^2– from DMS oxidation was significant only within the boundary layer and that transport from Asia dominated the sulfur cycle in the free troposphere. The existence of a sea-salt inversion layer was reflected in the profiles of those aerosol components, e.g., Na⁺ and NO₃ ^–, which were predominantly present as coarse particles. Our results show that long-range transport at mid-tropospheric levels plays an important role in determining the chemical composition of the atmosphere even in apparently remote northern hemispheric regions.     

Airborne measurements of dimethylsulfide,sulfur dioxide,and aerosol ions over the Southern Ocean South of Australia

Vertical distributions of dimethylsulfide (DMS), sulfur dioxide (SO₂), aerosol methane-sulfonate (MSA), non-sea-salt sulfate (nss-SO₄ ^2-), and other aerosol ions were measured in maritime air west of Tasmania (Australia) during December 1986. A few cloudwater and rainwater samples were also collected and analyzed for major anions and cations. DMS concentrations in the mixed layer (ML) were typically between 15–60 ppt (parts per trillion, 10^–12; 24 ppt=1 nmol m^–3 (20°C, 1013 hPa)) and decreased in the free troposphere (FT) to about <1–2.4 ppt at 3 km. One profile study showed elevated DMS concentrations at cloud level consistent with turbulent transport (cloud pumping) of air below convective cloud cells. In another case, a diel variation of DMS was observed in the ML. Our data suggest that meteorological rather than photochemical processes were responsible for this behavior. Based on model calculations we estimate a DMS lifetime in the ML of 0.9 days and a DMS sea-to-air flux of 2–3 mol m^–2 d^–1. These estimates pertain to early austral summer conditions and southern mid-ocean latitudes. Typical MSA concentrations were 11 ppt in the ML and 4.7–6.8 ppt in the FT. Sulfur-dioxide values were almost constant in the ML and the lower FT within a range of 4–22 ppt between individual flight days. A strong increase of the SO₂ concentration in the middle FT (5.3 km) was observed. We estimate the residence time of SO₂ in the ML to be about 1 day. Aqueous-phase oxidation in clouds is probably the major removal process for SO₂. The corresponding removal rate is estimated to be a factor of 3 larger than the rate of homogeneous oxidation of SO₂ by OH. Model calculations suggest that roughly two-thirds of DMS in the ML are converted to SO₂ and one-third to MSA. On the other hand, MSA/nss-SO₄ ^2- mole ratios were significantly higher compared to values previously reported for other ocean areas suggesting a relatively higher production of MSA from DMS oxidation over the Southern Ocean. Nss-SO₄ ^2- profiles were mostly parallel to those of MSA, except when air was advected partially from continental areas (Africa, Australia). In contrast to SO₂, nss-SO₄ ^2- values decreased significantly in the middle FT. NH₄ ⁺/nss-SO₄ ^2- mole ratios indicate that most non-sea-salt sulfate particles in the ML were neutralized by ammonium.     

Measurements of ozone and its precursor nitrogen dioxide and crop yield losses due to cumulative ozone exposures over 40 ppb (AOT40) in rural coastal southern India

Measurements of ground level ozone (O₃), nitrogen dioxide (NO₂) and meteorological parameters (air temperature, relative humidity and wind speed and direction) has been made for 3 years from March 2007 to February 2010 at Nagercoil (8.2°N, 77.5°E, 23 m above sea level), an equatorial rural coastal site of southern India. The monthly average of daytime maximum of O₃ concentrations ranged from 28 to 50 parts per billion (ppb) with an annual average of 19.8 ppb. Similarly, monthly average of NO₂ concentration ranged from 3.4 ppb to 7.7 ppb with an annual average of 5.3 ppb. The monthly variation of meteorological parameters shows the little changes being a coastal site. The estimated summer crops yield losses by 1.1–15.6 % from present O₃ concentration level associated with AOT40 index 3.1–5 ppm h.     

Spatiotemporal analysis of particulate matter, sulfur dioxide and carbon monoxide concentrations over the city of Rio de Janeiro, Brazil

Time series of pollutants and weather variables measured at four sites in the city of Rio de Janeiro, Brazil, between 2002 and 2004, were used to characterize temporal and spatial relationships of air pollution. Concentrations of particulate matter (PM₁₀), sulfur dioxide (SO₂) and carbon monoxide (CO) were compared to national and international standards. The annual median concentration of PM₁₀ was higher than the standard set by the World Health Organization (WHO) on all sites and the 24?h means exceeded the standards on several occasions on two sites. SO₂ and CO did not exceed the limits, but the daily maximum of CO in one of the stations was 27% higher on weekends compared to weekdays, due to increased activity in a nearby Convention Center. Air temperature and vapor pressure deficit have both presented the highest correlations with pollutant??s concentrations. The concentrations of SO₂ and CO were not correlated between sites, suggesting that local sources are more important to those pollutants compared to PM₁₀. The time series of pollutants and air temperature were decomposed in time and frequency by wavelet analysis. The results revealed that the common variability of air temperature and PM₁₀ is dominated by temporal scales of 1?C8?days, time scales that are associated with the passage of weather events, such as cold fronts.     

A microscale model for air pollutant dispersion simulation in urban areas: Presentation of the model and performance over a single building

A microscale air pollutant dispersion model system is developed for emergency response purposes. The model includes a diagnostic wind field model to simulate the wind field and a random-walk air pollutant dispersion model to simulate the pollutant concentration through consideration of the influence of urban buildings. Numerical experiments are designed to evaluate the model's performance, using CEDVAL(Compilation of Experimental Data for Validation of Microscale Dispersion Models) wind tunnel experiment data, including wind fields and air pollutant dispersion around a single building. The results show that the wind model can reproduce the vortexes triggered by urban buildings and the dispersion model simulates the pollutant concentration around buildings well. Typically, the simulation errors come from the determination of the key zones around a building or building cluster. This model has the potential for multiple applications; for example, the prediction of air pollutant dispersion and the evaluation of environmental impacts in emergency situations; urban planning scenarios;and the assessment of microscale air quality in urban areas.     

空气质量监测、分析、预报国际研究计划及前沿问题

为了研究空气污染影响人类健康和经济社会可持续发展这一重要环境问题,世界气象组织全球大气观测计划(WMO-GAW)和国际全球大气化学计划(IGAC)共同发起了空气质量监测、分析、预报国际研究计划(Monitoring,Analysis,and Prediction of Air Quality;即MAP-AQ),并于2019年5月27—29日在WMO总部日内瓦组织召开了MAP-AQ专家指导委员会会议。     

Long-term simulations of the sulfur concentrations over the China, Japan and Korea: A model comparison study

Three comprehensive acid deposition models were used to simulate the sulfur concentrations over northeast Asia over the period covering entire year of 2002, and discussed the aggregated uncertainties and discrepancies of the three models. The participating models are from the countries participating in the project of Longrange Transboundary Air Pollutants in Northeast Asia (LTP): China, Japan and Korea. The Eulerian Model-3/CMAQ (by China), Regional Air Quality Model (RAQM, by Japan), and Comprehensive Acid Deposition Model (CADM, by Korea) were employed by each country with common emissions data established by the administrative agencies of China, Japan and Korea. The episodic simulation results between 1 to 15, March 2002 are also presented, during which aircraft measurements were carried out over the Yellow sea. The episodic results show both a wide short-term variability in simulations against measurements, and maximum concentration differences of 3～5 times among the three models, requiring that further attention before confidence among the three models can be claimed for short-term simulations. However, the year-long cumulative simulations showed almost the same general features, with lower aggregated uncertainties between the three models, produced by the long term integration over northeast Asia.     

Turbulent flux observations and modelling over a shallow lake and a wet grassland in the Nam Co basin,Tibetan Plateau

The Tibetan Plateau plays an important role in the global water cycle and is strongly influenced by climate change. While energy and matter fluxes have been more intensely studied over land surfaces, a large proportion of lakes have either been neglected or parameterised with simple bulk approaches. Therefore, turbulent fluxes were measured over wet grassland and a shallow lake with a single eddy-covariance complex at the shoreline in the Nam Co basin in summer 2009. Footprint analysis was used to split observations according to the underlying surface, and two sophisticated surface models were utilised to derive gap-free time series. Results were then compared with observations and simulations from a nearby eddy-covariance station over dry grassland, yielding pronounced differences. Observations and footprint integrated simulations compared well, even for situations with flux contributions including grassland and lake. The accessibility problem for EC measurements on lakes can be overcome by combining standard meteorological measurements at the shoreline with model simulations, only requiring representative estimates of lake surface temperature.     

The impacts of urbanization on air quality over the Pearl River Delta in winter: roles of urban land use and emission distribution

In this study, ideal but realistic numerical experiments are performed to explore the relative effects of changes in land use and emission distribution on air quality in the Pearl River Delta (PRD) region in winter. The experiments are accomplished using the Lagrangian particle transport and dispersion model FLEXPART coupled with the Weather Research and Forecasting model under different scenarios. Experiment results show that the maximum changes in daily mean air pollution concentration (as represented by SO₂ concentration) caused by land use change alone reaches up to 2?×?10^?6 g m^?3, whereas changes in concentrations due to the anthropogenic emission distribution are characterized by a maximum value of 6?×?10^?6 g m^?3. Such results reflect that, although the impacts of land use change on air quality are non-negligible, the emission distribution exerts a more significant influence on air quality than land use change. This provides clear implications for policy makers to control urban air pollution over the PRD region, especially for the urban planning in spatial arrangements for reasonable emissions.     

Modelling of the nighttime nitrogen and sulfur chemistry in size resolved droplets of an orographic cloud

A chemistry module has been incorporated into a Lagrangian type model that computes the dynamics and microphysics of an orographical cloud formed in moist air flowing over the summit of Great Dun Fell (GDF) in England. The cloud droplets grow on a maritime aerosol which is assumed to be an external mixture of sea-salt particles and ammonium-sulfate particles. The dry particle radii are in the range 10 nm<r<1 µm. The gas-phase chemical reaction scheme considers reactions of nitrogen compounds that are important at night. The treatment of scavenging of gases into the aqueous phase in the model takes into account the different solubilities and accommodation coefficients. The chemistry in the aqueous phase focusses on the oxidation of S(IV) via different pathways.Sensitivity analyses have been performed to investigate deviations from gas-liquid equilibria according to Henry's law and also to study the influence of iron and of nitrogen compounds on the aqueous-phase oxidation of dissolved SO₂. When addressing these questions, special attention has been given to the dependence on the droplet size distribution and on the chemical composition of the cloud condensation nuclei on which the droplets have formed. It was found that the oxidation of S(IV) via a chain reaction of sulfur radicals can be important under conditions where H₂O₂ is low. However, major uncertainties remain with respect to the interaction of iron with the radical chain. It was shown that mixing of individual cloud droplets, which are not in equilibrium according to Henry's law, can result in a bulk sample in equilibrium with the ambient air. The dependence of the aqueous-phase concentrations on the size of the cloud droplets is discussed for iron, chloride and NO₃.     

Grab sampling for the determination of sulfur dioxide and dimethyl sulfide in air by isotope dilution gas chromatography/mass spectrometry

Developments allowing the direct determination of sulfur dioxide and dimethyl sulfide in grab samples by gas chromatography/mass spectrometry with isotopically labeled standards (GC/MS/ILS) are reported. Isotopomers of DMS and SO₂ are used as internal standards. Spiked air samples are dried to a dew point of <–60 °C and trapped cryogenically in loops of Teflon tubing. Sealed samples are transported to the laboratory under liquid nitrogen and later subjected to GC/MS analysis. Holding times of up to one month do not result in significant sample loss. For samples collected in a clean marine environment, concentrations of SO₂ and DMS greater than 5 and 8 pptv, respectively, are significantly different from blanks at the 95% confidence level. Average measurement precision derived from a propagation of errors are 9% for SO₂ and 42% for DMS at concentrations from 5–15 pptv.Improvements are outlined which should provide sensitivity and precision comparable to that of on-site GC/MS. The technique will allow increased flexibility for the determination of trace sulfur species in the field under conditions where deployment of a mass spectrometer is not possible.     

Evaluation of global climate model on performances of precipitation simulation and prediction in the Huaihe River basin

Using climate models with high performance to predict the future climate changes can increase the reliability of results. In this paper, six kinds of global climate models that selected from the Coupled Model Intercomparison Project Phase 5 (CMIP5) under Representative Concentration Path (RCP) 4.5 scenarios were compared to the measured data during baseline period (1960–2000) and evaluate the simulation performance on precipitation. Since the results of single climate models are often biased and highly uncertain, we examine the back propagation (BP) neural network and arithmetic mean method in assembling the precipitation of multi models. The delta method was used to calibrate the result of single model and multimodel ensembles by arithmetic mean method (MME-AM) during the validation period (2001–2010) and the predicting period (2011–2100). We then use the single models and multimodel ensembles to predict the future precipitation process and spatial distribution. The result shows that BNU-ESM model has the highest simulation effect among all the single models. The multimodel assembled by BP neural network (MME-BP) has a good simulation performance on the annual average precipitation process and the deterministic coefficient during the validation period is 0.814. The simulation capability on spatial distribution of precipitation is: calibrated MME-AM > MME-BP > calibrated BNU-ESM. The future precipitation predicted by all models tends to increase as the time period increases. The order of average increase amplitude of each season is: winter > spring > summer > autumn. These findings can provide useful information for decision makers to make climate-related disaster mitigation plans.     

Regional climate modelling over complex terrain: an evaluation study of COSMO-CLM hindcast model runs for the Greater Alpine Region

In this study the results of the regional climate model COSMO-CLM (CCLM) covering the Greater Alpine Region (GAR, 4°–19°W and 43°–49°N) were evaluated against observational data. The simulation was carried out as a hindcast run driven by ERA-40 reanalysis data for the period 1961–2000. The spatial resolution of the model data presented is approx. 10 km per grid point. For the evaluation purposes a variety of observational datasets were used: CRU TS 2.1, E-OBS, GPCC4 and HISTALP. Simple statistics such as mean biases, correlations, trends and annual cycles of temperature and precipitation for different sub-regions were applied to verify the model performance. Furthermore, the altitude dependence of these statistical measures has been taken into account. Compared to the CRU and E-OBS datasets CCLM shows an annual mean cold bias of ?0.6 and ?0.7 °C, respectively. Seasonal precipitation sums are generally overestimated by +8 to +23 % depending on the observational dataset with large variations in space and season. Bias and correlation show a dependency on altitude especially in the winter and summer seasons. Temperature trends in CCLM contradict the signals from observations, showing negative trends in summer and autumn which are in contrast to CRU and E-OBS.