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Volume 15, issue 2
Atmos. Chem. Phys., 15, 951–972, 2015
https://doi.org/10.5194/acp-15-951-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Special issue: Atmospheric impacts of Eastern Asia megacities

Atmos. Chem. Phys., 15, 951–972, 2015
https://doi.org/10.5194/acp-15-951-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 28 Jan 2015

Research article | 28 Jan 2015

Atmospheric wet and dry deposition of trace elements at 10 sites in Northern China

Y. P. Pan and Y. S. Wang Y. P. Pan and Y. S. Wang
  • State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry (LAPC), Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China

Abstract. Atmospheric deposition is considered to be a major process that removes pollutants from the atmosphere and an important source of nutrients and contaminants for ecosystems. Trace elements (TEs), especially toxic metals deposited on plants and into soil or water, can cause substantial damage to the environment and human health due to their transfer and accumulation in food chains. Despite public concerns, quantitative knowledge of metal deposition from the atmosphere to ecosystems remains scarce. To advance our understanding of the spatiotemporal variations in the magnitudes, pathways, compositions and impacts of atmospherically deposited TEs, precipitation (rain and snow) and dry-deposited particles were collected simultaneously at 10 sites in Northern China from December 2007 to November 2010.

The measurements showed that the wet and dry depositions of TEs in the target areas were orders of magnitude higher than previous observations within and outside China, generating great concern over the potential risks. The spatial distribution of the total (wet plus dry) deposition flux was consistent with that of the dry deposition, with a significant decrease from industrial and urban areas to suburban, agricultural and rural sites, while the wet deposition exhibited less spatial variation. In addition, the seasonal variation of wet deposition was also different from that of dry deposition, although they were both governed by the precipitation and emission patterns.

For the majority of TEs that exist as coarse particles, dry deposition dominated the total flux at each site. This was not the case for potassium, nickel, arsenic, lead, zinc, cadmium, selenium, silver and thallium, for which the relative importance between wet and dry deposition fluxes varied by site. Whether wet deposition is the major atmospheric cleansing mechanism for the TEs depends on the size distribution of the particles.

We found that atmospheric inputs of copper, lead, zinc, cadmium, arsenic and selenium were of the same magnitude as their increases in the topsoil of agricultural systems. At a background forest site in Northern China, the total deposition flux of lead observed in this study (14.1 mg m−2 yr−1) was twice that of the critical load calculated for temperate forest ecosystems in Europe. These findings provide baseline data needed for future targeting policies to protect various ecosystems from long-term heavy metal input via atmospheric deposition.

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This paper presents the first concurrent measurements of wet and dry deposition of various trace elements in Northern China, covering an extensive area over 3 years in a global hotspot of air pollution. The unique field data can serve as a sound basis for the validation of regional emission inventories and biogeochemical or atmospheric chemistry models. The findings are very important for policy makers to create legislation to reduce the emissions and protect soil and water from air pollution.
This paper presents the first concurrent measurements of wet and dry deposition of various trace...
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