Asian dust storms can increase the level of atmospheric pollution over regions downwind of dust storms and may have adverse health effects on residents along the sandstorm transmission route. This study was the first to report the concentration levels, properties and possible sources of environmentally persistent free radicals (EPFRs) and oxidative potential in atmospheric PM2.5 at the three sites of Erenhot, Zhangbei, and Jinan along the transport route of Asian dust storms during the occurrence of Asian dust storms in the spring of 2016. Under non-sandstorm weather conditions, the average EPFR concentrations at the three sites were Zhangbei>Jinan>Erenhot, while the PM-induced oxidative potential levels were Erenhot>Jinan>Zhangbei. The PM2.5 concentration increased significantly during dust storm events, and the total atmospheric concentration of EPFRs (spins/m3) and total oxidation potential (a.u./m3) of PM2.5 simultaneously increased. However, the EPFR concentration in PM2.5 (spins/g) and the unit mass of the PM oxidation potential (a.u./g) were significantly reduced. Electron paramagnetic resonance analysis combined with backward trajectory analysis and MODIS products showed that Asian dust storms can carry EPFRs over long distances. Correlation analysis showed that the atmospheric concentrations of EPFRs were positively correlated with elemental carbon (EC) for the Zhangbei and Jinan samples but were not significantly correlated with EC for the Erenhot samples, indicating that combustion may be an important source of EPFRs for the Zhangbei and Jinan samples. In contrast, the EPFRs in the Erenhot samples were more affected by dust/sand. The EPFR concentration levels showed a significant positive correlation with the oxidation potentials for the Erenhot and Zhangbei samples and showed negative correlations for the Jinan samples, suggesting that the EPFRs in the Erenhot and Zhangbei samples may provide an important contribution to the oxidative stress in PM2.5. In contrast, the oxidation potential for the Jinan samples was mainly caused by substances other than EPFRs. This study presents a basic understanding of the potential health effects of Asian dust storms, and this information can be used to assess the health risks of Asian dust storms in future studies.

Dust aerosols play key roles in affecting regional and global climate through their direct, indirect, and semi-direct effects. Dust events have decreased rapidly since the 1980s in East Asia, particularly over northern China, primarily because of changes in meteorological parameters (e.g. surface wind speed and precipitation). In this study, we found that winter (December–January–February) Arctic amplification associated with weakened temperature gradients along with decreased zonal winds is primarily responsible for the large decline in following spring (March–April–May) dust event occurrences over northern China since the mid-1980s. A dust index was developed for northern China by combining the daily frequency of three types of dust event (dust storm, blowing dust, and floating dust). Using the empirical orthogonal function (EOF) analysis, the first pattern of dust events was obtained for spring dust index anomalies, which accounts for 56.2% of the variability during 1961–2014. Moreover, the enhanced Arctic amplification and stronger Northern Hemisphere annular mode (NAM) in winter can result in the anticyclonic anomalies over Siberia and Mongolia, while cyclonic anomalies over East Europe in spring. These results are significantly correlated with the weakened temperature gradients, increased precipitation and soil moisture, and decreased snow cover extent in the mid-latitude over Northern Hemisphere. Based on the future predictions obtained from the Fifth Climate Models Intercomparison Project (CMIP5), we found that the dust event occurrences may continually decrease over northern China due to the enhanced Arctic amplification in future climate.

Mineral dust interacts with radiation and cloud microphysics in East Asia can affect local and regional climate. In this study, we found that the occurrences of dust storms, blowing dust, and floating dust over northern China has decreased 76.7%, 68.5%, and 64.5% considerably since the beginning of this century. Based on a multi-dimensional ensemble empirical mode decomposition (MEEMD) method, a steady decrease in zonal maximum wind speed (up to −0.95 m/s) in the Northern Hemisphere was largely responsible for this recent decline in dust event occurrences. Then, a new detection technique that combines multi-satellite datasets with surface observations of dust events is developed to estimate the contribution of anthropogenic dust column burden from disturbed soils to the observed total dust. It is found that the percentage of the anthropogenic dust column burdens to total mineral dust is up to 76.8% by human activities during 2007–2014 in eastern China, but only less than 9.2% near desert source regions in northwestern China. However, we note that the anthropogenic effects on the dust loading for both regions are non-negligible.

A snow survey was carried out to collect 13 surface snow samples (10 for fresh snow, and 3 for aged snow) and 79 subsurface snow samples in seasonal snow at 13 sites across northeastern China in January 2014. A spectrophotometer combined with chemical analysis was used to quantify snow particulate absorption by insoluble light-absorbing particles (ILAPs, e.g., black carbon, BC; mineral dust, MD; and organic carbon, OC) in snow. Snow albedo was measured using a field spectroradiometer. A new radiative transfer model (Spectral Albedo Model for Dirty Snow, or SAMDS) was then developed to simulate the spectral albedo of snow based on the asymptotic radiative transfer theory. A comparison between SAMDS and an existing model – the Snow, Ice, and Aerosol Radiation (SNICAR) – indicates good agreements in the model-simulated spectral albedos of pure snow. However, the SNICAR model values tended to be slightly lower than those of SAMDS when BC and MD were considered. Given the measured BC, MD, and OC mixing ratios of 100–5000, 2000–6000, and 1000–30 000 ng g⁻¹, respectively, in surface snow across northeastern China, the SAMDS model produced a snow albedo in the range of 0.95–0.75 for fresh snow at 550 nm, with a snow grain optical effective radius (R_eff) of 100 µm. The snow albedo reduction due to spherical snow grains assumed to be aged snow is larger than fresh snow such as fractal snow grains and hexagonal plate or column snow grains associated with the increased BC in snow. For typical BC mixing ratios of 100 ng g⁻¹ in remote areas and 3000 ng g⁻¹ in heavy industrial areas across northern China, the snow albedo for internal mixing of BC and snow is lower by 0.005 and 0.036 than that of external mixing for hexagonal plate or column snow grains with R_eff of 100 µm. These results also show that the simulated snow albedos by both SAMDS and SNICAR agree well with the observed values at low ILAP mixing ratios but tend to be higher than surface observations at high ILAP mixing ratios.