Conference Agenda

In this project we study air quality over China using satellite observations, especially their spatial and temporal variability. The latest years of satellite observations of NO2 and SO2 concentrations have been used to infer NOx and SO2 emissions to augment our earlier trend analysis.
In addition, a new SO2 inversion algorithm for use with TROPOMI SO2 observations is under development. Since February 2018 NO2 observations became routinely available from the TROPOMI instrument on S5p. For this a snow-cloud differentiation method has been developed to drastically increase the number of observations over snow surfaces, like Norther China in winter and regions in the Himalaya mountains.
Both the SO2 and NOx emissions are used in the regional chemical-transport model CHIMERE. This model participates in an ensemble forecast of 9 operational models for East China. The ensemble forecast is compared to in-situ observations and performs better than each individual model.

Solar Global Radiation And Its Variation Mechanism At A Subtropical Site In China

Jianhui Bai¹ Gerrit De Leeuw² Larisa Sogacheva² Ronald Van Der A³ Yimei Wu¹ Xiaowei Wan¹

1. LAGEO, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China

2. Finnish Meteorological Institute, Climate Research Unit, Helsinki, Finland

3. Royal Netherlands Meteorological Institute, De Bilt, The Netherlands

Abstract Measurements Of Solar Radiation And Meteorological Parameters Were Carried Out At A Subtropical Pinus Forest Site In China From May, 2013 To December, 2016. An Empirical Model Of Solar Global Radiation Has Been Developed For Different Atmospheric Conditions And The Calculated Solar Global Radiation Is In Agreement With The Observed. This Empirical Model Was Used To Calculate The Attenuation Of Solar Global Irradiance In The Atmosphere Caused By Absorbing And Scattering Substances. Sensitivity Analysis Shows That Solar Global Radiation Is More Sensitive To Changes In Water Vapor Absorption Than To Changes In Scattering Factors, S/Q (S And Q Are Solar Direct And Global Radiation, Respectively). Aerosol Optical Depth (AOD) Is An Important Parameter To Improve The Understanding Of The Scattering Of Solar Radiation. The Relationship Between The Attenuation Factor (AF) And AOD Was Determined And Used To Estimate AOD.

Key Words: Solar Global Radiation, Absorbing And Scattering Factors, Energy, AOD, Climate.

Sentinel 5 Precursor (S5P) satellite was launched into a polar orbit in October 2017, carrying the
TROPOMI instrument. S5P has sun synchronous orbit with an equator crossing time of 13:30 LT.
TROPOMI achieves an almost daily coverage, due to the wide swath width of 2600 km.
The near-real-time (NRTI) ozone total column is based on the two step DOAS approach, consisting of a
slant column retrieval and an iterative AMF-calculation. In this study we present tropospheric ozone
columns based on total column from S5P and stratospheric column based on 4D-Var assimilation of
Aura MLS ozone profiles. To avoid potential errors we use d only cloud free TROPOMI data.
After a brief introduction of the methods the data will be compared to other tropospheric data
satellite data i.e. HCHO and NO2 S5P. The study will focus be on the first year of TROPOMI
observation over East Asia.

Dose-Response Functions (DRFs) are a very important model tool for estimating the deterioration – degradation of structural materials used in both modern constructions and cultural heritage monuments due to atmospheric pollution and climatological parameters. In current international literature, available DRFs use ground-based air pollution and climatological data to model materials’ deterioration. This limits DRFs use only to areas where the necessary ground based data, is available. In a previous study were presented the results of the attempt to develop a new type of DRFs that modeled the deterioration – degradation of materials, especially carbon steel and limestone, using only satellite data. The term “Satellite Sensed Data-Dose Response Functions (SSD-DRFs)” was proposed for this new kind of DRFs. This study presents the preliminary results of the attempt on the development of SSD-DRFs to assess the deterioration – degradation of zinc and modern glass materials. Modern glass is used to monitor materials surface soiling rather than as structural material. The development of SSD-DRFs provides the opportunity to monitor cultural heritage monuments in areas where ground-based data are not available, extends the use of satellite data by introducing a completely new field of implementation and is largely in line with the European Commission’s effort supporting the Cultural Heritage preservation and management by using Copernicus data and services.

Analysis of PM_2.5 readings taken at the US embassy in Beijing since 2009 reveals that winter haze over North China Plain (NCP) peaked in 2012 and 2013 and there was an improvement in air quality until 2016. The variation of wintertime PM_2.5 from 2009 to 2016 is influenced by both emission changes and meteorology conditions, and in this study we quantified the relative contributions from these two aspects. The sensitivity simulation by the GEOS-Chem model suggested that the emission reductions over NCP in 2013-2017 caused a 10% decrease of the regional mean PM_2.5 concentration in 2016 winter compared to the 2012 winter level. We removed the emission influence on PM_2.5 concentration to get the PM_2.5 that influenced by meteorology (met-influenced PM_2.5). For the met-influenced PM_2.5, compared to the original observation, the percentage of clean days (daily PM_2.5 concentration less than 75 μg/m³) decreases while that of the polluted (daily PM_2.5 concentration between 75 μg/m³ and150 μg/m³) and heavily polluted (daily PM_2.5 concentration between 150 μg/m³and250 μg/m³) days increases. However, proportion of the extremely polluted (daily PM_2.5 concentration exceeds 250 μg/m³) days stays unchanged, even if the emission reduction is doubled, indicating that the extremely polluted situation over NCP is dominated by the meteorological conditions, and the emission control from 2013 to 2017 has little effects on the extremely polluted days. We developed an effective haze day index (HDI) to represent the weather conditions conducive to haze days. HDI is constructed based on the normalized near surface meridional wind (V850), temperature difference (δT) between near surface (850hPa) and upper atmosphere (250hPa), and the relative humidity on 1000hPa (RH1000). HDI correlates well with daily PM_2.5 with the correlation coefficient of 0.65, and is skillful to detect 72% of the severe haze days (daily PM_2.5 concentration exceeds 150 μg/m³), ranging 48% in 2014 winter to 94% in 2012 winter. The components of HDI can also reveal the relative importance of the three meteorological variables in haze days. On average, the anomalously high meridional winds is the main cause of severe haze these years, while in 2012 winter, the relative humidity favorable for secondary aerosols formation is the largest contributor to haze.

In this poster, we present ground based remote sensing activities at Hefei, China. It includes site report for both TCCON and NDACC-IRWG observations and some research activities based on these observations.

Abstract: A ground-based low-resolution (0.5 cm⁻¹) Fourier Transform Spectrometer (FTS), the EM27/SUN, is used for determining the total column XCO2 and XCH4 of the atmosphere by analysing direct solar radiation. A ground-based high-resolution Fourier transform spectrometer (FTS) station has been established in Hefei, China to remotely measure CO2, CO and other greenhouse gases based on near-infrared solar absorption spectra. The observations of low-resolution FTS were compared with the temporally coinciding on-site measurements taken with a high-resolution FTIR spectrometer. EM27 captures the seasonal variation of CO2 and CH4.Also, there is a offset between the values of EM27 and FTS, ranging from about 1.35ppm to 1.55ppm for XCO2, and about 7.01ppb to 9.74ppb for XCH4, respectively. The observation results demonstrate the ability of the portable EM27 spectrometer as a promising addition to the TCCON FTIR sites, suitable for remote areas with low infrastructure.

In this poster, the seasonal evolution of O3 and its photochemical production regime in a polluted region of eastern China between 2014 and 2017 has been investigated. We used tropospheric ozone (O3), carbon monoxide (CO) and formaldehyde (HCHO, a marker of VOCs (volatile organic compounds)) partial columns derived from high resolution Fourier transform spectrometry (FTS), tropospheric nitrogen dioxide (NO2, a marker of NOx (nitrogen oxides)) partial column deduced from Ozone Monitoring Instrument (OMI), surface meteorological data, and a back trajectory cluster analysis technique.

The multi-field-of-view solar photometer was developed by Anhui Institute of Optics and Fine Mechanics, Hefei Institutes of Physical Science, Chinese Academy of Sciences which consists of three wavelengths (442 nm, 670 nm, 880 nm) and three fields of view (0.8°, 2°, 5°) for direct sunlight. In this paper, we explores the possibility to retrieve the cloud optical thickness and effective particle radius of thin cirrus clouds by using forward scatter radiation in small angles in terms of model simulation. The radiant fluxes of different wavelengths in different fields of view are calculated based on the ice cloud characters of scattering phase function and single scattering albedo of nine ice crystal particles provided by Yang (2013) by using libRadtran software and their trends varying with the cloud optical thickness and the effective particle radius are analyzed. It is obvious that the radiant fluxes change with the cloud optical thickness for larger cloud optical thickness means longer the ice water path and more portion of the radiation is scattered. They change much more slowly with the effective particle radius and only at a small cloud optical thickness they increase with the increasing of the effective particle radius. Therefore, it is possible to retrieve the cloud optical thickness and the effective particle radius of the thin cirrus (namely the cloud optical thickness is small) simultaneously by using small angle scattering. At the same time, we calculate the difference of the radiant flux between two different fields of view, no matter which two field of view are used, the radiance flux difference is not sensitive to the effective particle radius, but sensitive to the cloud optical thickness. With the increasing of cloud optical thickness, the radiant flux difference becomes smaller gradually. This feature can also be used to retrieve the cloud optical thickness. The radiant flux ratios for arbitrary different fields of view show a good tendency to decrease gradually for droxtal particles as the effective particle radius increases,but it is not sensitive to other particle habits. Fortunately there will be a significant improvement with the effective particle radius when we find the ratio of the radiant flux difference, especially for plates. The ratios of the radiant flux difference increase gradually with the increasing of the effective particle radius. It can be seen that the inversion of the effective particle radius needs to be used several values in combination with each other. In summary, the radiant flux difference between two field of view to retrieve the cloud optical thickness and the ratio or difference ratio to retrieve the effective particle radius can be useful to ensure that it is not sensitive to another factor while doing retrievals of one factor. But this is only the analysis result of theoretical simulation calculation and We still need to do a lot of work for experimental observation and combine them together for more detailed analysis in the future.

Over a decade of OMI observations provide insight into the rapidly changing air quality levels in China. Global documentation of key atmospheric pollutant gases such as nitrogen dioxide (NO₂) and sulfur dioxide (SO₂) allow the study of anthropogenic and natural emissions on different spatial scales.

Based on bottom-up emissions inventories, Chinese SO₂ emissions were the world’s largest, particularly over the North China Plain. SO₂ sources are related to major coal-fired power plants and industrial activities such as oil and gas refining, and metal smelting. Similarly, the highest NOx emissions are observed over the world’s most populated (increased mobile sources), highly urbanized and industrialized regions.

Despite the growth of the economy in the rapidly developing China over the past two decades, a substantial overall decrease in the SO₂ and NOx emissions has been observed with different patterns between the species. We investigate the spatial variability of these trends and we identity their origin. The differences between the spatial distributions of SO₂ and NOx emissions over the Chinese domain are related to differences in economic and technological activity, and regional environmental policies.

Government efforts to restrain emissions from power plants and industrial sectors (e.g. installation of de-sulfurization devices) have resulted in decreasing SO₂ and NOx emissions since approximately 2007 and 2011, respectively. We use the SO₂/NOx ratio to locate and characterize the emissions sources since, to some extent, it reflects the level of the regional modernization and helps us identify the source sector. For instance, the megacity of Shanghai and the areas around it are highly populated with cleaner power plants compared to other regions, therefore a relatively low SO₂/NOx ratio is observed.

Tropospheric ozone plays an important role in atmospheric processes. Hence, the acquisition of tropospheric ozone content from satellite observations is a crucial challenge for atmospheric pollution research. In this study, tropospheric ozone columns over China were retrieved from total ozone columns measured by the Ozone Monitoring Instrument (OMI) and ozone profile of the Microwave Limb Scanner (MLS). Inversion results were then compared and validated with Electrochemical Concentration Cell (ECC) ozonesonde observations, ground-based surface ozone measurements, and simulation results from the Regional Atmospheric Modeling System – Community Multiscale Air Quality Model (RAMS-CMAQ). Validation results in China during 2005–2014 showed a correlation coefficient of 0.67 between the OMI-MLS tropospheric ozone and ozonesonde data, although lower correlations (~0.36) were found over northeastern China, which were attributed to satellite observation errors at high latitudes. Comparisons between ground-based surface data and RAMS-CMAQ simulated results also demonstrated high correlations. Except for in Northeast and South China, the OMI-MLS tropospheric ozone correlates well with ground-based data (0.63) and RAMS-CMAQ simulated results (0.71). The weak correlation in South China was likely caused by the presence of ozone-generating mechanisms or sources in the upper troposphere, in addition to anthropogenic surface emissions of ozone precursors. Moreover, long-term seasonal and spatial distribution characteristics of tropospheric ozone over China were also determined, and the results show that the OMI-MLS tropospheric ozone has a trend consistent with that of ground-based and model data, accurately reflecting the seasonal changes of tropospheric ozone in China. Thus, this study demonstrates that OMI-MLS tropospheric ozone can accurately indicate changes of surface ozone concentrations. Satellite remote sensing can compensate for ground-based surface ozone observation shortages and improve the spatiotemporal coverage of near-surface ozone monitoring.