Long-Term Variation of Black Carbon Absorption Aerosol Optical Depth from AERONET Data over East Asia

Absorption aerosol optical depth induced by black carbon (AAODBC) was retrieved using the depolarization ratio and single scattering albedo provided by the Aerosol Robotic Network (AERONET) inversion products over East Asia. Our analysis considered AERONET data from six sites in East Asia that are mostly affected by anthropogenic pollution, black carbon (BC) emissions, and natural mineral dust, during the period 2001–2018. We identified a rapid reduction in total aerosol optical depth (AODT) of −0.0106 yr−1 over Beijing, whereas no considerable trend was observed at the Korean and Japanese sites. The long-term data for AAODBC showed decreasing trends at all sites. We conclude that successful emission control policies were the major underlying driver of AODT and AAODBC reductions over East Asia, particularly in China, during the study period. Values of the AAODBC/AODT ratio revealed that, although these policies were successful, the Chinese government needs to undertake stricter measures toward reducing BC emissions. We found that AAODBC follows seasonal trends, peaking in the colder months. This suggests that in East Asia, particularly in China, domestic coal burning is still of concern.

The spatially heterogeneous response of aerosol properties to anthropogenic activities and meteorology changes in China during 1980-2018 based on the singular value decomposition method

The unsustainable and rapid economy development brings air pollution prominently in China. In the last decade, the haze weather and its influencing mechanism across China have received increasingly attention. Although previous research has extensively focused on the characteristics of aerosols, better understanding of long-term variation in aerosols and their determinants since the Reform and Opening-up still lack in China. Furthermore, the previous studies exploring the influencing mechanism behind haze episodes by using statistical method only reflect correlation between pollutant concentration and indicators at single station, which cannot consider the remote influences resulting from atmosphere transport. In this research, we investigated the spatiotemporal pattern of aerosol optical depth (AOD) and aerosol species in China during 1980-2018 and explored the spatially heterogeneous response of AOD and aerosol component to meteorological conditions and urbanization based on singular value decomposition (SVD) method. The results indicated that AOD exhibited an upward trend in nearly 40 years, especially in eastern China with the fastest growth of sulfate aerosol. The heterogeneity of determinants revealed a great gap in anthropogenic activities and meteorological influences on aerosol varing regions. In eastern China, anthropogenic activities should be closely monitored. Besides, scientific desert governance and urban construction exert positive impact on air pollution in Xinjiang province.

Microscopic comparison of aerosol particles collected at an urban site in North China and a coastal site in Japan

In order to understand the physicochemical properties of aerosol particles in Japan and China, transmission electron microscopy was used to analyze individual aerosol particles collected at two very different environmental sites, i.e., a continental site (T1) in North China and a coastal site (T2) in Japan in springtime. The average PM_2.5 concentration (52μg/m³) at T1 was much higher than T2 (20μg/m³) from 20 to 23 March 2014. Our study shows that sulfur-organic matter (S-OM) particles were the most abundant at both T1 and T2, and individual spherical primary organic matter (POM) particles were only observed at T1. More anthropogenic fly ash and metal particles were observed at T1, consistent with the heavier air pollution at T1 than T2, and the overall complexity of aerosol composition at T1 exceeded that at T2, due to the influence of regional industrial emissions. Further examination of S-OM particles suggest that S-OM coated particles accounted for 29.6% of total observed particles at T2 but only 8.6% at T1. However, the average thickness of OM coating was larger at T2 than at T1, indicating that the particles at T2 had aged longer than those at T1. These comparisons suggest that the OM coating thickness on sulfate depends on the transport distance of the air mass and on the concentration of atmospheric oxidants but should not be used to represent pollution levels. Compared with the coastal air in Japan, we know that urban aerosol particles in North China not only attain high concentrations but also have more complex aerosol components.

Sources of atmospheric black carbon and related carbonaceous components at Rishiri Island, Japan: The roles of Siberian wildfires and of crop residue burning in China

A field study was conducted to clarify sources of atmospheric black carbon and related carbonaceous components at Rishiri Island, Japan. We quantified equivalent black carbon (eBC) particle mass and the absorption Ångström exponent (AAE), atmospheric CO and CH₄, in addition to levoglucosan in total suspended particles, a typical tracer of biomass burning. Sixteen high eBC events were identified attributable to either anthropogenic sources or biomass burning in Siberia/China. These events were often accompanied by increases of co-emitted gases such as CH₄ and CO. Specifically, we observed pollution events with elevated eBC, AAE, levoglucosan, and CH₄CO slope in late July 2014, which were attributed to forest fires in Siberia by reference to the FLEXPART model footprint and fire hotspots. In autumn, drastic increases of eBC, AAE, and levoglucosan were observed, accompanied by an eBC-CO slope of >15 ng m^-3/ppb, resulting from long-range transport of emissions from extensive burning of crop residue on the Northeast China Plain. Other than the sources of fossil fuel combustion in China and forest fires in Siberia, we report for the first time that pollution events in northern Japan are caused by crop residue burning in China. This study elucidated valuable information that will improve understanding of the effects of biomass burning in East Asia on atmospheric carbonaceous components.

Spatial and Temporal Variations in Characteristic Ratios of Elemental Carbon to Carbon Monoxide and Nitrogen Oxides across the United States

A ratio-based method is used to characterize anthropogenic elemental carbon (EC_a) using in situ measurements and emissions of carbon monoxide (CO) and nitrogen oxides (NO_x). We use long-term records of ground-based measurements from the U.S. Environmental Protection Agency (EPA) Air Quality System and Interagency Monitoring of Protected Visual Environments to assess the patterns in anthropogenic combustion ratios (ΔEC_a/ΔCO and ΔEC_a/ΔNO_x) across the U.S. Petroleum Administration for Defense Districts (PADD) regions for the years 2000-2015. We investigate the change in these ratios between the periods 2000-2007 and 2008-2015. Overall, ΔEC_a/ΔCO ratios increase by 0.7-82% and ΔEC_a/ΔNO_x by 6.8-104% across the East and West PADD regions. The urban West showed the largest increase relative to other regions. This is mainly attributed to a 13-23% increase in ΔEC_a during the winter and fall seasons and significant reductions in urban ΔNO_x (except in winter). We also find that emission ratios derived from the EPA's National Emission Inventory (NEI) overestimate (underestimate) the increase in the observed enhancement ratios in the East (West). Analyses of changes in NEI emissions in the West reveal (a) smaller reductions in NEI emissions for NO_x from the off-road sector and (b) an increase in PM_2.5 (particulate matter 2.5 μm or less in diameter) emissions from commercial/residential combustion and smaller reductions in nonroad emissions.

Quantifying sources of elemental carbon over the Guanzhong Basin of China: A consistent network of measurements and WRF-Chem modeling

We conducted a year-long WRF-Chem (Weather Research and Forecasting Chemical) model simulation of elemental carbon (EC) aerosol and compared the modeling results to the surface EC measurements in the Guanzhong (GZ) Basin of China. The main goals of this study were to quantify the individual contributions of different EC sources to EC pollution, and to find the major cause of the EC pollution in this region. The EC measurements were simultaneously conducted at 10 urban, rural, and background sites over the GZ Basin from May 2013 to April 2014, and provided a good base against which to evaluate model simulation. The model evaluation showed that the calculated annual mean EC concentration was 5.1 μgC m(-3), which was consistent with the observed value of 5.3 μgC m(-3). Moreover, the model result also reproduced the magnitude of measured EC in all seasons (regression slope = 0.98-1.03), as well as the spatial and temporal variations (r = 0.55-0.78). We conducted several sensitivity studies to quantify the individual contributions of EC sources to EC pollution. The sensitivity simulations showed that the local and outside sources contributed about 60% and 40% to the annual mean EC concentration, respectively, implying that local sources were the major EC pollution contributors in the GZ Basin. Among the local sources, residential sources contributed the most, followed by industry and transportation sources. A further analysis suggested that a 50% reduction of industry or transportation emissions only caused a 6% decrease in the annual mean EC concentration, while a 50% reduction of residential emissions reduced the winter surface EC concentration by up to 25%. In respect to the serious air pollution problems (including EC pollution) in the GZ Basin, our findings can provide an insightful view on local air pollution control strategies.

Interprovincial Reliance for Improving Air Quality in China: A Case Study on Black Carbon Aerosol

Black carbon (BC) is of global concern because of its adverse effects on climate and human health. It can travel long distances via atmospheric movement and can be geographically relocated through trade. Here, we explored the integrated patterns of BC transport within 30 provinces in China from the perspective of meteorology and interprovincial trade using the Weather Research and Forecasting with Chemistry (WRF/Chem) model and multiregional input-output analysis. In general, cross-border BC transport, which accounts for more than 30% of the surface concentration, occurs mainly between neighboring provinces. Specifically, Hebei contributes 1.2 μg·m(-3) BC concentration in Tianjin. By contrast, trade typically drives virtual BC flows from developed provinces to heavily industrial provinces, with the largest net flow from Beijing to Hebei (4.2 Gg). Shanghai is most vulnerable to domestic consumption with an average interprovincial consumption influence efficiency of 1.5 × 10(-4) (μg·m(-3))/(billion Yuan·yr(-1)). High efficiencies (∼8 × 10(-5) (μg·m(-3))/(billion Yuan·yr(-1))) are also found from regions including Beijing, Jiangsu, and Shanghai to regions including Hebei, Shandong, and Henan. The above source-receptor relationship indicates two control zones: Huabei and Huadong. Both mitigating end-of-pipe emissions and rationalizing the demand for pollution-intense products are important within the two control zones to reduce BC and other pollutants.

Are emissions of black carbon from gasoline vehicles overestimated? Real-time, in situ measurement of black carbon emission factors

Accurately quantifying black carbon (BC) emission factors (EFs) is a prerequisite for estimation of BC emission inventory. BC EFs determined by measuring BC at the roadside or chasing a vehicle on-road may introduce large uncertainty for low emission vehicles. In this study, BC concentrations were measured inside the tailpipe of gasoline vehicles with different engine sizes under different driving modes to determine the respective EFs. BC EFs ranged from 0.005-7.14 mg/kg-fuel under the speeds of 20-70 km/h, 0.05-28.95 mg/kg-fuel under the accelerations of 0.5-1.5m/s(2). Although the water vapor in the sampling stream could result in an average of 12% negative bias, the BC EFs are significantly lower than the published results obtained with roadside or chasing vehicle measurement. It is suggested to conduct measurement at the tailpipe of gasoline vehicles instead of in the atmosphere behind the vehicles to reduce the uncertainty from fluctuation in ambient BC concentration.

Trends of the sunshine duration and diffuse radiation percentage on sunny days in urban agglomerations of China during 1960-2005

The long-term observational data of sunshine duration (SD) and diffuse radiation percentage (defined as diffuse solar radiation/total solar radiation, DRP) on sunny days during 1960-2005 were analyzed in 7 urban agglomerations and the whole of China. The results show that the sunny sunshine duration (SSD) has decreased significantly except at a few stations over northwestern China in the past 46 years. An obvious decrease of the SSD is found in eastern China, with the trend coefficients lower than -0.8. Accompanied by the SSD decline, the sunny diffuse radiation percentage (SDRP) in most stations shows obvious increasing trends during the 46 years. The averaged SDRP over China has increased 2.33% per decade, while the averaged SSD shows a decrease of -0.13 hr/day per decade. The correlation coefficient between SDRP and SSD is -0.88. SSD decreased over urban agglomerations (small to large city clusters) in the past 46 years, especially in large cities and medium cities, due to the strong anthropogenic activities and air pollution represented by aerosol option depth (AOD) and tropospheric column NO2 (TroNO2). On the regional scale, SSD has an opposite trend from SDRP during 1960 to 2005, and the variation trends of regional mean values of SSD and SDRP in southeastern China are more pronounced than those in northwestern China.

Using Bayesian optimization method and FLEXPART tracer model to evaluate CO emission in East China in springtime

Carbon monoxide (CO) is of great interest as a restriction factor for pollutants related to incomplete combustions. This study attempted to evaluate CO emission in East China using the analytical Bayesian inverse method and observations at Mount Hua in springtime. The mixing ratio of CO at the receptor was calculated using 5-day source-receptor relationship (SRR) simulated by a Lagrangian Particle Dispersion Model (FLEXPART) and CO emission flux. The stability of the inversion solution was evaluated on the basis of repeated random sampling simulations. The inversion results demonstrated that there were two city cluster regions (the Beijing-Tianjin-Hebei region and the low reaches of the Yangtze River Delta) where the difference between a priori (Intercontinental Chemical Transport Experiment-Phase B, INTEX-B) and a posteriori was statistically significant and the a priori might underestimate the CO emission flux by 37 %. A correction factor (a posteriori/a priori) of 1.26 was suggested for CO emission in China in spring. The spatial distribution and magnitude of the CO emission flux were comparable to the latest regional emission inventory in Asia (REAS2.0). Nevertheless, further evaluation is still necessary in view of the larger uncertainties for both the analytical inversion and the bottom-up statistical approaches.