Global modeling of cloudwater acidity, rainwater acidity, and acid inputs to ecosystems

doi:10.5194/acp-2020-485

GSTDTAP > 地球科学

DOI	10.5194/acp-2020-485
	Global modeling of cloudwater acidity, rainwater acidity, and acid inputs to ecosystems
	Viral Shah, Daniel J. Jacob, Jonathan M. Moch, Xuan Wang, and Shixian Zhai
	2020-06-22
发表期刊	Atmospheric Chemistry and Physics
出版年	2020
英文摘要	Cloudwater acidity affects the atmospheric chemistry of sulfate and organic aerosol formation, halogen radical cycling, and trace metal speciation. Rainwater acidity including post-depositional inputs adversely affects soil and freshwater ecosystems. Here we use the GEOS-Chem model of atmospheric chemistry to simulate the global distributions of cloud- and rainwater acidity, and the total acid inputs to ecosystems from wet deposition. The model accounts for strong acids (H₂SO₄, HNO₃, HCl), weak acids (HCOOH, CH₃COOH, CO₂, SO₂), and weak bases (NH₃, dust and sea salt aerosol alkalinity). We compile a global dataset of cloudwater pH measurements for comparison with the model. The global mean observed cloudwater pH is 5.2 ± 0.9, compared to 5.0 ± 0.8 in the model, with a range of 3 to 8 depending on region. The lowest values are over East Asia and the highest values are over deserts. Cloudwater pH over East Asia is low because of large acid inputs (H₂SO₄, HNO₃), despite NH₃ and dust neutralizing 70 % of these inputs. Cloudwater pH is typically 4–5 over the US and Europe. Carboxylic acids account for less than 25 % of cloudwater H⁺ in the northern hemisphere on an annual basis, but 25–50 % in the southern hemisphere and over 50 % in the southern tropical continents where they push the cloudwater pH below 4.5. Anthropogenic emissions of SO₂ and NO_x (precursors of H₂SO₄ and HNO₃) are decreasing at northern mid-latitudes, but the effect on cloudwater pH is strongly buffered by NH₄⁺ and carboxylic acids. The global mean rainwater pH is 5.5 in GEOS-Chem, higher than the cloudwater pH because of dilution and below-cloud scavenging of NH₃ and dust. GEOS-Chem successfully reproduces the rainwater pH observations in North America, Europe, and eastern Asia. Carboxylic acids, which are undetected in routine observations due to biodegradation, lower the annual mean rainwater pH in these areas by 0.2 units. The acid wet deposition flux to terrestrial ecosystems taking into account the acidifying potential of NO₃⁻ and NH₄⁺ in N-saturated ecosystems exceeds 50 meq m⁻² a⁻¹ in East Asia and the Americas, which would affect sensitive ecosystems. NH₄⁺ is the dominant acidifying species in wet deposition, contributing 41 % of the global acid flux to continents under N-saturated conditions.
领域	地球科学
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文献类型	期刊论文
条目标识符	http://119.78.100.173/C666/handle/2XK7JSWQ/278122
专题	地球科学
推荐引用方式 GB/T 7714	Viral Shah, Daniel J. Jacob, Jonathan M. Moch, Xuan Wang, and Shixian Zhai. Global modeling of cloudwater acidity, rainwater acidity, and acid inputs to ecosystems[J]. Atmospheric Chemistry and Physics,2020.
APA	Viral Shah, Daniel J. Jacob, Jonathan M. Moch, Xuan Wang, and Shixian Zhai.(2020).Global modeling of cloudwater acidity, rainwater acidity, and acid inputs to ecosystems.Atmospheric Chemistry and Physics.
MLA	Viral Shah, Daniel J. Jacob, Jonathan M. Moch, Xuan Wang, and Shixian Zhai."Global modeling of cloudwater acidity, rainwater acidity, and acid inputs to ecosystems".Atmospheric Chemistry and Physics (2020).