Elsevier

Atmospheric Environment

Volume 39, Issue 9, March 2005, Pages 1749-1758
Atmospheric Environment

Chemical characteristics of aerosols transported from Asia to the East China Sea: an evaluation of anthropogenic combined nitrogen deposition in autumn

https://doi.org/10.1016/j.atmosenv.2004.11.037Get rights and content

Abstract

Deposition of terrestrial aerosols is one of the major means of fertilizing the oligotrophic ocean waters. In order to understand the biogeochemical significance of aerosols transported from the Asian continent, and deposited over the East China Sea, we studied their chemical properties by making continuous measurements on board R/V Hakuho Maru in autumn, a season of lower dust events.

Outflows of anthropogenic substances were observed over the East China Sea. The average concentration of non-sea-salt (nss)-SO42− in aerosols was 8.7±6.8 μg m−3, a value typical for polluted atmosphere of a highly industrialized urban area in South China. Fine mode NH4+ mainly occurred as (NH4)2SO4 and/or NH4HSO4 while in coarse mode it was formed from intermodal coagulation of ammonium particles in fine and coarse aeorosols. On the other hand, the mean concentration of NO3 (1.8±1.2 μg m−3) was lower than that in the urban atmosphere. Non-sea-salt SO42− were derived from combustion sources and marine biological processes, the latter accounting to 0–38%. Nitrate in coarse mode was associated with Ca2+ and Na+ perhaps due to replacement reactions.

Our estimates of the annual atmospheric aerosol deposition fluxes of NH4+ and NO3 to the East China Sea were 270 Gg N yr−1 and 160 Gg N yr−1, respectively. These atmospheric inputs are comparable to the riverine inputs of the Changjiang River. The total combined nitrogen deposition could account for a biological fixation of about 2.5 Tg C (approximately 0.1–9% of the new production) in the East China Sea annually, which could actually be larger since the autumn season experience minimal dust storms.

Introduction

Industrial growth is rapid in East Asia. The emission of anthropogenic substances in East Asia has been on the rise due to the use of fossil fuels, industrialization (e.g., Kato and Akimoto, 1992) and due to the lack of waste control practices (Huh and Chen, 1999). In particular, nitrogen oxide (NOx) emissions in East Asia increased by 65% from 1975 to 1987 (Akimoto and Narita, 1994). It is predicted that NOx emissions will increase approximately 5-fold from 1990 to 2020 (van Aardenne et al., 1999; Akimoto, 2003). The increasing industrial emissions have made several ecosystems significant recipients of atmospheric pollutants (Galloway et al., 1995). Sulfate and nitrate are the most common compounds contributing to atmospheric acidity, and their deposition affects the pH of surface water (Lestari et al., 2003). On the other hand, the atmospheric deposition of combined nitrogen, ammonium and nitrate, is an important nutrient supply to the oceans (Duce et al., 1991; Paerl, 1997; Spokes et al., 2000). It has been suggested that these deposits affect productivity and ecosystems in oceanic and coastal areas (e.g., Owens et al., 1992; Uematsu et al., 2004).

The western North Pacific receives a large influx of mineral particles and pollutants from East Asia through atmospheric long-range transport (Uematsu et al., 1983; Tsunogai et al., 1985; Gao et al., 1992). The East China Sea is one of the largest marginal seas in the world and is situated between the east coast of China and the western North Pacific (Lin et al., 2000). High biological activity in the East China Sea is maintained by nutrients supplied from the Changjiang River, one of the largest rivers in the world, and the Kuroshio upwelling (Chen and Chen, 2003).

Several of the previous atmospheric observations were made in spring due to the occurrence of frequent dust events under the influence of strong seasonal westerly winds (e.g., Gao et al., 1992), but only a few studies in autumn (e.g., Hatakeyama et al., 1995). Further, atmospheric nutrients supply to the East China Sea was not considered in the previous studies. The present attempts to investigate the nature and sources of aerosols through the study of their chemical properties, their transports to the study area, the deposition of the combined nitrogen species over the East China Sea and to evaluate their significance to biological fixation of carbon dioxide.

Section snippets

Methods

Fig. 1 shows the track of Leg 2 of the KH02-3 cruise conducted on board the vessel R/V Hakuho-maru between 26 September 2002 and 9 October 2002. A high-volume virtual impactor air sampler (Kimoto Electric Co., Ltd., AS-9) was used to collect atmospheric aerosols on Teflon filter papers (Toyo Roshi Kaisha, Ltd., PF040, 90 mm in diameter). The sampler used an inertial force to separate atmospheric aerosols according to their aerodynamic diameters, which were segregated into fine (<2.5 μm) and

Variations in particle number density

Fig. 2 shows the variations in particle number densities, where peaks in these reflect the times of ship passage through outflow of air masses blown from the continent. Four pronounced peaks were observed. Number densities of particles larger than 0.1 μm frequently exceeded 1000 cm−3 with the highest value of 4000 cm−3. Values below 100 cm−3 were very few. Matsumoto and Uematsu (2004) reported that number densities of particles larger than 0.1 μm were <100 cm−3 over the remote western North Pacific,

Conclusions

We made continuous measurements of atmospheric aerosols over the western North Pacific and the East China Sea. The conclusions of this study are:

  • (1)

    The highest concentration of total nss-SO42− observed over the central East China Sea was close to the highest value in an urban atmosphere in a highly industrialized area. However, the highest concentration of total NO3 was lower than that in polluted air. This is probably because NO3 was removed from the atmosphere faster than nss-SO42− and due to

Acknowledgments

We are thankful to the principal investigator Prof. M. Kawabe, Ocean Research Institute, University of Tokyo, and to the captain and crew of the R/V Hakuho Maru for the KH02-3 Cruise. We are grateful to the two anonymous reviewers for their constructive and encouraging comments on our manuscript. We are also thankful to Dr. M. Dileep Kumar of National Institute of Oceanography of India, for providing critical comments and help in revising the manuscript.

This study was carried out under the

References (41)

  • C.J. Ottley et al.

    The spatial distribution and particle size of some inorganic nitrogen species over the North Sea

    Atmospheric Environment

    (1992)
  • J.A. van Aardenne et al.

    Anthropogenic NOx emissions in Asia in the period 1990–2020

    Atmospheric Environment

    (1999)
  • G.T. Wolff

    On the nature of nitrate in coarse continental aerosols

    Atmospheric Environment

    (1984)
  • S.G. Yeatman et al.

    Comparisons of coarse-mode aerosol nitrate and ammonium at two polluted coastal sites

    Atmospheric Environment

    (2001)
  • J. Zhang

    Nutrient elements in large Chinese estuaries

    Continental Shelf Research

    (1996)
  • H. Zhuang et al.

    Size distributions of particulate sulfate, nitrate, and ammonium at a coastal site in Hong Kong

    Atmospheric Environment

    (1999)
  • H. Akimoto

    Global air quality and pollution

    Science

    (2003)
  • S.T. Bates et al.

    Variations in the methanesulfonate to sulfate molar ratio in submicrometer marine aerosol particles over the South Pacific Ocean

    Journal of Geophysical Research

    (1992)
  • L.Y. Chen et al.

    Nitrate-based new production and its relationship to primary production and chemical hydrography in spring and fall in the East China Sea

    Deep-Sea Research II

    (2003)
  • R.A. Duce et al.

    The atmospheric input of trace species to the world ocean

    Global Biogeochemical Cycles

    (1991)
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