Bingliang Zhuang

Temporal characterization and regional contribution to O3 and NOx at an urban and a suburban site in Nanjing, China.

To improve our understanding of the interplay among local and regional photochemical pollutants in the typical city of the Yangtze River Delta (YRD) region, the concurrent observation of O3 and NOx concentrations at an urban and a suburban site in Nanjing during 2008 is presented. In general, the annual mean O3 concentration is 2.35ppbv lower in the downtown than at suburban due to higher NOx pollution levels correlated with heavy traffic. At both sites, O3 shows a distinct seasonality with the spring maximum and the winter minimum, while the minimum concentration of NOx appears in summertime. Besides the chemical processes of O3 sensitivity in the daytime and the NOx titration at night, meteorological conditions also play an essential role in these monthly and diurnal variations. The ozone weekend effect that can be attributed to the weekly routine of human activities is observed in the urban atmosphere of Nanjing as well, with O3 concentrations 2.09ppbv higher and NOx concentrations 6.20ppbv lower on weekends than on weekdays. The chemical coupling of NO, NO2 and O3 is investigated to show that the OX-component (O3 and NO2) partitioning point occurs at about 35ppbv for NOx, with O3 being the dominant form at lower levels and NO2 dominating at higher levels. And it is also discovered that the level of OX is made up of two contributions, including the regional contribution affected by regional background O3 level and the local contribution correlated with the level of primary pollution. The diurnal peak of regional contribution appears 2-5h after the peak of local contribution, implying that OX in Nanjing might prominently affected by the pollutants from a short distance. The highest regional contribution and the second highest local contribution lead to the spring peak of O3 observed in Nanjing, whereas the highest local contribution and the moderate regional contribution make the O3 concentrations in summer higher than those in autumn and winter. Our results reveal the important environment impacts from meteorological conditions and human activities in the YRD region, and can help to understand O3 pollution in these polluted areas by just using the conventional observations.

Source apportionment of size-fractionated particles during the 2013 Asian Youth Games and the 2014 Youth Olympic Games in Nanjing, China

In this study, samples of size-fractionated particulate matter were collected continuously using a 9-size interval cascade impactor at an urban site in Nanjing, before, during and after the Asian Youth Games (AYG), from July to September of 2013, and the Youth Olympic Games (YOG), from July to September of 2014. First, elemental concentrations, water-soluble ions including Cl-, NO3-, SO42-, NH4+, K+, Na+ and Ca2+, organic carbon (OC) and elemental carbon (EC) were analysed. Then, the source apportionment of the fine and coarse particulate matter was carried out using the chemical mass balance (CMB) model. The average PM10 concentrations were 90.4±20.0μg/m3 during the 2013 AYG and 70.6±25.3μg/m3 during the 2014 YOG. For PM2.1, the average concentrations were 50.0±12.8μg/m3 in 2013 and 34.6±17.0μg/m3 in 2014. Investigations showed that the average concentrations of particles declined significantly from 2013 to 2014, and concentrations were at the lowest levels during the events. Results indicated that OC, EC, sulfate and crustal elements have significant monthly and size-based variations. The major components, including crustal elements, water-soluble ions and carbonaceous aerosol accounted for 75.3-91.9% of the total particulate mass concentrations during the sampling periods. Fugitive dust, coal combustion dust, iron dust, construction dust, soil dust, vehicle exhaust, secondary aerosols and sea salt have been classified as the main emissions in Nanjing. The source apportionment results indicate that the emissions from fugitive dust, which was the most abundance emission source during the 2013 AYG, contributed to 23.0% of the total particle mass. However, fugitive dust decreased to 6.2% of the total particle mass during the 2014 YOG. Construction dust (14.7% versus 7.8% for the AYG and the YOG, respectively) and secondary sulfate aerosol (9.3% versus 8.0% for the AYG and the YOG, respectively) showed the same trend as fugitive dust, suggesting that the mitigation measures of controlling particles from the paved roads, construction and industry worked more efficiently during the YOG.

Impact of aerosols on regional climate in southern and northern China during strong/weak East Asian summer monsoon years

In this work, we mainly simulate the effects of aerosols on regional climate in southern China (SC) and northern China (NC) and compare the differences of aerosol climatic effects in strong/weak summer monsoon years with a modified regional climate model RegCM4. The results show that the total climatic effects of aerosols cause the decline of averaged air temperature and precipitation of SC and NC in summer. In NC, the strength of temperature drop in strong summer monsoon years is higher than that in weak summer monsoon years, indicating the possible impact from the different changes of radiation, circulation, and precipitation. The decrease of precipitation is more significant in NC in weak summer monsoon years, while it is stronger in SC in strong summer monsoon years due to the difference of aerosol distribution as well as the effects on circulation and cloud microphysics processes. Besides, aerosol effects also cause a decrease of zonal wind at 850 hPa in SC and an increase in NC. The cooling center is more northerly and stronger in strong monsoon year, while it is more southerly and weaker in weak summer monsoon years, which results in the differences of vertical circulation anomaly and meridional wind anomaly at 850 hPa. In weak summer monsoon years, meridional wind at 850 hPa is increased in NC, while it is found to be decreased in SC. In strong summer monsoon years, meridional winds at 850 hPa in both NC and SC are weakened. However, the decrease in SC is much more distinct and clear.

Characterization of major natural and anthropogenic source profiles for size-fractionated PM in Yangtze River Delta

Samples of size-fractionated particles were collected from local natural and anthropogenic sources in two industrial cities in the Yangtze River Delta, using either grab/resuspension sampling or ambient air sampling. The chemical characterizations of twenty one source profiles were obtained, based on elements (Al, As, Ca, Cd, Cr, Cu, Fe, K, Mg, Mn, Na, Pb and Zn), soluble ions (Cl-, NO3-, SO42-, NH4+, K+, Na+ and Ca2+) and carbonaceous material such as organic carbon (OC) and elemental carbon (EC). The profiles vary between sources from different areas, as well as between different particulate sizes. Results show that particulate matter that originated as soil dust, construction dust and fugitive dust is typically rich in crustal elements, especially Al, Ca, Fe and Mg, while the presence of calcium is found to be a hallmark of the cement industry and ceramic industry. Dominant compositions of particles from coal-fired power plants are variable, with OC ranging from 2.2%-27%. Garbage-fired power plant and cooking smoke particulate emissions are enriched in Na, Cl-, OC and K due to the presence of salty and organic matter. The element Fe, ranging from 6.1% to 26.0%, is found to be an important marker for steel production dust. Vehicle exhaust profiles are characterized by high abundances of OC (12.1%-53.6%) and EC (3.9%-20.0%). Burning of straw results in K (1.6%-7.2%) and OC (12.4%-25.9%) being the dominant composition. Preliminary work has also been done on establishing local industrial profiles such as textile, ceramic and electroplating industries. This work could be used in receptor model studies to estimate the contributions of different sources to the size-fractionated particulate matter in the Yangtze River Delta.

Modeling of urban heat island and its impacts on thermal circulations in the Beijing–Tianjin–Hebei region, China

Through regulating the land–atmosphere energy balance, urbanization plays an important role in modifying local circulations and cross-border transport of air pollutants. The Beijing–Tianjin–Hebei (BTH) metropolitan area in northern China is frequently influenced by complex atmospheric thermal circulations due to its special topography and geographic position. In this study, the Weather Research and Forecasting (WRF) model combined with remote sensing is used to explore the urbanization impacts on local circulations in the BTH region. The urban heat island (UHI) effect generated around Beijing and Tianjin shows complex interactions with local thermal circulations. Due to the combined effects of UHI and topography, the UHI circulation around Beijing and valley breeze at the southern slopes of Yan Mountain are coupled together to reinforce each other. At the coastal cities, the increased land/sea temperature gradient considerably accelerates the sea breeze along Bohai Bay and moves the sea breeze front further inland to reach as far as Beijing. This study may lay a foundation for the better understanding of air pollutant dispersion on complex terrain.

Assessment of direct radiative forcing due to secondary organic aerosol over China with a regional climate model

Using the regional climate model (RegCM4), optical depth and shortwave (SW) direct radiative forcing (DRF) of secondary organic aerosol (SOA) are investigated over China during the summer period. The biogenic emission and gas phase chemistry modules are updated to investigate α-pinene and limonene emissions and their reactions with atmosphere oxidants. The VBS (volatility basis set) model is implemented into RegCM4 to illustrate gas-particle partition process. During the study period (July 2006), the mean surface concentration and column burden of anthropogenic SOA (ASOA) over China are 1.90 µg m−3 and 4.50 mg m−3, respectively. The ones of biogenic SOA (BSOA) are 2.00 and 3.35 mg m−3, respectively. Monthly mean calculated optical depths (at 550 nm) are 0.020 and 0.013 for ASOA and BSOA. The domain averaged simulated ASOA direct SW radiative forcing at surface and at the top of atmosphere (TOA) are −1.21 and −0.66 W m−2. For BSOA, the surface and TOA SW DRF are −0.75 and −0.46 W m−2. The errors induced by applying optical parameters of primary organic aerosol for SOA DRF modelling are also accessed. For DRF at TOA, it will increase by 156 and 161% for ASOA and BSOA. Though the optical parameters applied in this study are still rough, especially for intermediate SOA, this is a first step to apply explicit optical parameters for both ASOA and BSOA in DRF estimation.

Improved meteorology and ozone air quality simulations using MODIS land surface parameters in the Yangtze River Delta urban cluster, China

Land surface parameters play an important role in the land-atmosphere coupling and thus are critical to the weather and dispersion of pollutants in the atmosphere. This work aims at improving the meteorology and air quality simulations for a high-ozone (O3) event in the Yangtze River Delta urban cluster of China, through incorporation of satellite-derived land surface parameters. Using Moderate Resolution Imaging Spectroradiometer (MODIS) input to specify the land cover type, green vegetation fraction, leaf area index, albedo, emissivity, and deep soil temperature provides a more realistic representation of surface characteristics. Preliminary evaluations reveal clearly improved meteorological simulation with MODIS input compared with that using default parameters, particularly for temperature (from −2.5 to −1.7°C for mean bias) and humidity (from 9.7% to 4.3% for mean bias). The improved meteorology propagates through the air quality system, which results in better estimates for surface NO2 (from 11.5 to 8.0 ppb for mean bias) and nocturnal O3 low-end concentration values (from −18.8 to −13.6 ppb for mean bias). Modifications of the urban land surface parameters are the main reason for model improvement. The deeper urban boundary layer and intense updraft induced by the urban heat island are favorable for pollutant dilution, thus contributing to lower NO2 and elevated nocturnal O3. Furthermore, the intensified sea-land breeze circulation may exacerbate O3 pollution at coastal cities through pollutant recirculation. Improvement of mesoscale meteorology and air quality simulations with satellite-derived land surface parameters will be useful for air pollution monitoring and forecasting in urban areas.

Eddy covariance tilt corrections over a coastal mountain area in South-east China: Significance for near-surface turbulence characteristics

Turbulence characteristics of an atmospheric surface layer over a coastal mountain area were investigated under different coordinate frames. Performances of three methods of coordinate rotation: double rotation (DR), triple rotation (TR), and classic planar-fit rotation (PF) were examined in terms of correction of eddy covariance flux. Using the commonly used DR and TR methods, unreasonable rotation angles are encountered at low wind speeds and cause significant run-to-run errors of some turbulence characteristics. The PF method rotates the coordinate system to an ensemble-averaged plane, and shows large tilt error due to an inaccurate fit plane over variable terrain slopes. In this paper, we propose another coordinate rotation scheme. The observational data were separated into two groups according to wind direction. The PF method was adapted to find an ensemble-averaged streamline plane for each group of hourly runs with wind speed exceeding 1.0 m s−1. Then, the coordinate systems were rotated to their respective best-fit planes for all available hourly observations. We call this the PF10 method. The implications of tilt corrections for the turbulence characteristics are discussed with a focus on integral turbulence characteristics, the spectra of wind-velocity components, and sensible heat and momentum fluxes under various atmospheric stabilities. Our results show that the adapted application of PF provides greatly improved estimates of integral turbulence characteristics in complex terrain and maintains data quality. The comparisons of the sensible heat fluxes for four coordinate rotation methods to fluxes before correction indicate that the PF10 scheme is the best to preserve consistency between fluxes.

The Impacts of Meteorology on the Seasonal and Interannual Variabilities of Ozone Transport From North America to East Asia

The transport of North American (NA) ozone to East Asia is investigated through the analysis of a 20-year simulation (1987-2006) using a global chemical transport model (GEOS-Chem) and forward trajectories during the 1990s at three NA sites. NA ozone mainly influences northern East Asia (> 30 °N), where NA ozone in the free troposphere peaks in spring and fall (~12 ppbv). At the surface, NA ozone ranges from 2 to 7 ppbv and peaks in winter, ~50% of which is from the NA boundary layer. The seasonality of the imported NA ozone reflects the combined effects of meteorology and chemistry. In summer, NA ozone can be diverted from reaching East Asia by strong downdrafts behind the European trough. In winter, the prevailing monsoon climate in East Asia can boost downdrafts of NA ozone to the surface. In spring and fall, the westerlies are stronger and shift further south than in summer, bring more NA ozone to the East Asian (EA) free troposphere than in summer. The imported NA ozone at the EA surface also varies with interannual meteorology. This interannual variation is found to closely correlate to the East Asian winter monsoon (EAWM). The stronger the EAWM in a winter is, the stronger are the downdrafts bringing more NA ozone to the EA surface in that winter and the subsequent spring. Because the anthropogenic NA emissions have decreased since 1999, the year an emission inventory was used in the simulations, the simulated NA influence may serve as an upper limit.

Characteristics of ozone and particles in the near-surface atmosphere in urban area of the Yangtze River Delta, China

11 To improve the understanding of the interactions between particles and trace gases in a typical city 12 of the YRD region, continuous measurements of particles and trace gases were made at an urban 13 site in Nanjing during cold seasons in 2016 in this study. The average of particles, including black 14 carbon (BC), PM2.5, and PM10 are 2.602 1.720 μg/m, 58.2 36.8 μg/m, and 86.3 50.8 μg/m, 15 respectively, while the average of trace gases, which contain CO, O3, NOx, and NOy, are 850.9 16 384.1, 37.7 33.5, 23.5 14.7, and 32.8 22.3 ppb, respectively. Compared to National Ambient 17 Air Quality Standards in China (NAAQS-CN), we found 48 days excess of PM2.5, 14 days excess 18 of PM10, and 40 days excess of O3. The particles, CO, and nitrogen oxide concentrations shared a 19 similar pattern of seasonality and diurnal cycles, which are different from O3. The former ones are 20 all high in DJF and at rush hours, while the latter one had high loadings in the daytime, especially 21 Atmos. Chem. Phys. Discuss., https://doi.org/10.5194/acp-2018-927 Manuscript under review for journal Atmos. Chem. Phys. Discussion started: 15 October 2018 c