A comprehensive analysis of the spatio-temporal variation of urban air pollution in China during 2014–2018

The Taklimakan Desert (TD) and Gobi Desert (GD) are two of the most important dust sources in East Asia, and have important impact on energy budgets, ecosystems and water cycles at regional and even global scales. To investigate the contribution of the TD and the GD to dust concentrations in East Asia as a whole, dust emissions, transport, and deposition over the TD and the GD in different seasons from 2007 to 2011 were systematically compared, based on the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem). Dust emissions, uplift, and long-range transport related to these two dust source regions were markedly different due to differences in topography, elevation, thermal conditions, and atmospheric circulation. Specifically, the topography of the GD is relatively flat, and at a high elevation, and the area is under the influence of two jet streams at high altitudes, resulting in high wind speeds in the upper atmosphere. Deep convective mixing enables the descending branch of jet streams to continuously transport momentum downward to the mid-troposphere, leading to enhanced wind speeds in the lower troposphere over the GD which favors the vertical uplift of the GD dust particles. Therefore, the GD dust was very likely to be transported under the effect of strong westerly jets, and thus played the most important role in contributing to dust concentrations in East Asia. Approximately 35% and 31% of dust emitted from the GD transported to remote areas in East Asia in spring and summer, respectively. The TD has the highest dust emission capabilities in East Asia, with emissions of about 70.54 Tg yr−1 in spring, accounting for 42% of the total dust emissions in East Asia. However, the TD is located in the Tarim Basin and surrounded by mountains on three sides. Furthermore, the dominant surface wind direction is eastward and the average wind speed at high altitudes is relatively small over the TD. As a result, the TD dust particles are not easily transported outside the Tarim Basin, such that most of the dust particles are re-deposited after uplift, at a total deposition rate of about 40 g m−2. It is only when the TD dust particles are uplifted above 4 km, and entrained in westerlies that they begin to undergo a long-range transport. Therefore, the contribution of the TD dust to East Asian dust concentrations was relatively small. Only 25% and 23% of the TD dust was transported to remote areas over East Asia in spring and summer, respectively.

Comparison of dust emissions, transport, and deposition between the Taklimakan Desert and Gobi Desert from 2007 to 2011

Spatio-temporal patterns of air pollution in China from 2015 to 2018 and implications for health risks.

Temporal and spatial variations in sand and dust storm events in East Asia from 2007 to 2016: Relationships with surface conditions and climate change

In an environment with many local, remote, persistent, and episodic sources of pollution, meteorology is the primary factor that drives periods of unhealthy air quality and reduced visibility. The 2016 Korea-United States Air Quality (KORUS-AQ) field study provides a unique opportunity to examine the impact of meteorology on the relative influence of local and transboundary pollution. Much of the KORUS-AQ campaign can be grouped into four distinct research periods based on observed synoptic meteorology, including a period of complex aerosol vertical profiles driven by dynamic meteorology, stagnation under a persistent anticyclone, low-level transport and haze development, and a blocking pattern. These episodes are examined using a diverse archive of ground, airborne, and satellite data. While frontal boundaries are recognized as the primary mechanism driving pollution transport in eastern Asia, results show that they are not always related to sustained periods of hazardous air quality and reduced visibility at the surface. Significant long-range transport of pollution and dust was constrained to a few short events, suggesting that the majority of pollutants sampled during KORUS-AQ originated from local sources. A severe regional pollution episode is examined in detail, featuring dense haze and significant secondary particle formation within a shallow moist boundary layer. Observations during KORUS-AQ also highlight a rapid, 40 ppbv increase in ozone pollution as a strong sea breeze front traversed the Seoul Metropolitan Area. Representativeness of meteorology and pollution conditions measured by KORUS-AQ is considered by comparison with climatology. This analysis is an essential step toward improved local and regional forecasting of air quality and visibility.

Meteorology influencing springtime air quality, pollution transport, and visibility in Korea

. The Weather Research and Forecasting Model with chemistry (WRF-Chem model) was used to investigate a typical dust storm event that occurred from 18 to 23 March 2010 and swept across almost all of China, Japan, and Korea. The spatial and temporal variations in dust aerosols and the meteorological conditions over East Asia were well reproduced by the WRF-Chem model. The simulation results were used to further investigate the details of processes related to dust emission, long-range transport, and radiative effects of dust aerosols over the Taklimakan Desert (TD) and Gobi Desert (GD). The results indicated that weather conditions, topography, and surface types in dust source regions may influence dust emission, uplift height, and transport at the regional scale. The GD was located in the warm zone in advance of the cold front in this case. Rapidly warming surface temperatures and cold air advection at high levels caused strong instability in the atmosphere, which strengthened the downward momentum transported from the middle and low troposphere and caused strong surface winds. Moreover, the GD is located in a relatively flat, high-altitude region influenced by the confluence of the northern and southern westerly jets. Therefore, the GD dust particles were easily lofted to 4 km and were the primary contributor to the dust concentration over East Asia. In the dust budget analysis, the dust emission flux over the TD was 27.2 ± 4.1 µg m−2 s−1, which was similar to that over the GD (29 ± 3.6 µg m−2 s−1). However, the transport contribution of the TD dust (up to 0.8 ton d−1) to the dust sink was much smaller than that of the GD dust (up to 3.7 ton d−1) because of the complex terrain and the prevailing wind in the TD. Notably, a small amount of the TD dust (PM2.5 dust concentration of approximately 8.7 µg m−3) was lofted to above 5 km and transported over greater distances under the influence of the westerly jets. Moreover, the direct radiative forcing induced by dust was estimated to be −3 and −7 W m−2 at the top of the atmosphere, −8 and −10 W m−2 at the surface, and +5 and +3 W m−2 in the atmosphere over the TD and GD, respectively. This study provides confidence for further understanding the climate effects of the GD dust.

/pdf/emission-transport-and-radiative-effects-of-mineral-dust-3k4xfytku3.pdf

Emission, transport, and radiative effects of mineral dust from the Taklimakan and Gobi deserts: comparison of measurements and model results

S evere spring to early summer drought over Southwest China (SWC) in 2019 caught the public by surprise with its extreme intensity and damage (Ding and Gao 2020; Lu et al. 2021; Wang et al. 2021). Having still not fully recovered from this event, SWC then encountered one of its worst droughts on record in spring to early summer 2020 (the March–June mean ranks 13th and June ranks first in dryness since records began in 1961). Compared to the 2019 drought, the 2020 drought was episodic, developed rapidly from March to April due to the exceptionally high temperature and low precipitation, was slightly alleviated by sporadic precipitation during late April and May, and strengthened again to the lowest precipitation and highest temperature on record in June. This severe 2020 drought, especially in June, has raised questions about anthropogenic drought influences because of its large-scale damage to the local ecology, agriculture, and economy. Usually a humid region, SWC has suffered more frequent and severe droughts in recent decades (Li et al. 2019; Yan et al. 2017; Ding and Gao 2020). According to previous research on SWC droughts, persistent abnormal sea surface temperature (SST) over the tropical Pacific and Indian Oceans (Ju and Chen 2003; Liu et al. Fu Luo, Shanshan Wang, Yongli He, Yanxin Wang, and Hao Wang

Anthropogenic Warming Has Increased the 2020 Extreme Hot and Dry Conditions over Southwest China

In June‐July 2020, the Middle and Lower Yangtze River Region (MLYR) encountered the most severe precipitation event over the past 60 years. The Indian Ocean Dipole (IOD) in the previous autumn of the unusual precipitation event was the main contributing factor. Nonetheless, not every strong IOD event could bring anomalously high precipitation in the MLYR. This study showed significantly enhanced influence of IOD on East Asia climate since 2000. The IOD's effect on MLYR summer precipitation has strengthened significantly with the correlation coefficient up to 0.55 during 2000–2020. The northward movement of East Asia–Pacific pattern associated with IOD since 2000 (as compared with before) was primarily responsible for the enhanced effect. Since 2000, the MLYR has been controlled by a deep baroclinic instability system with anomalous low pressure in the lower troposphere and anomalous high pressure (completely different from before). Furthermore, the western Pacific subtropical high shifted northward and westerly jets were significantly enhanced with eastward expansion. All of these patterns contributed to the water vapor convergence and precipitation generation in the MLYR, which was not the case in the past. The record‐breaking IOD in 2019 autumn and the enhanced IOD's climatic effect in 2000–2020 contribute to the extreme Meiyu in 2020 jointly. The significant change in the influence of IOD and the enhanced climate effect of IOD highlight exciting new avenues for improving climate predictions in the MLYR.

Strengthened Impacts of Indian Ocean Dipole on the Yangtze Precipitation Contribute to the Extreme Rainfall of 2020 Meiyu Season

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Emission, transport, and radiative effects of mineral dust from the Taklimakan and Gobi deserts: comparison of measurements and model results

Anthropogenic Warming Has Increased the 2020 Extreme Hot and Dry Conditions over Southwest China

Strengthened Impacts of Indian Ocean Dipole on the Yangtze Precipitation Contribute to the Extreme Rainfall of 2020 Meiyu Season