Indeed, as seen in the last blog entry, when compared to shipping of goods by air, land, and rail, the shipping of goods by sea is a relatively cleaner form of transport. In this week’s blog entry, we will reveal how emissions from the shipping industry significantly contribute to air pollution. 

Emissions from shipping produce pollutants in the form of exhaust gases and particles. These include carbon dioxide (CO2), nitrogen oxides (NOx), sulfur dioxide (SO2), carbon monoxide (CO), volatile organic compounds (VOCs), particulate sulfate (SO4), black carbon (BC), particulate organic matter (OM) (Geels et al., 2021; Gong et al., 2018). 

Globally, these emissions are significant. For a start, the collective shipping industry contributes to around 940 million tonnes of CO2 annually (UKRI, 2021). This renders the industry to be a significant source of greenhouse gas emissions, accounting for around 2.5% of the world’s total CO2 emissions. In addition to CO2, shipping contributes to around 15% of global anthropogenic NOx and 5-8% of global SOx emissions (Eyring et al., 2005; Corbett et al., 2007).

Locally, many studies have also found shipping emissions to also contribute greatly to air pollution in coastal regions. In a review of research on shipping emissions in Europe by Viana et al. (2014), they found shipping to contribute to between 7-24% of NO2 levels (Figure 1), 1-7% of ambient air PM10 levels,, 1-14% of PM2.5, and at least 11% of PM1 (Figure 2). Similarly, Zhang et al. (2017) review of research on shipping emissions in China has found ship emissions at ports to significantly contribute to air pollution in coastal areas (Figures 3 & 4). 

Figure 1: Contribution from shipping emissions to air quality (NO2 and SO2 across Europe). (Source: Viana et al., 2014).

Figure 2: Contribution from shipping emissions to air quality (PM10, PM2.5 and PM1) across Europe. (Source: Viana et al., 2014).

Figure 3: Ship emission in ports in China reported in literature. (Source: Zhang et al., 2017).

Figure 4: Map representation of ship emissions of ports in China–Based on figures from the above table. (Source: Zhang et al., 2017).

These air pollutants can negatively affect the environment in three main ways : 

  1. The formation of ozone (O3),  SO4 particles from ship emissions, together with the direct emission of CO2 and BC, are climate-forcing agents, which subsequently impact the radiative balance of the earth, therefore contributing to global warming (Gong et al., 2018). 
  2. The release of SO2 and NOx also reacts with water vapour in the air, transforming into sulfuric acid (H2SO4) and nitric acid (HNO3). The subsequent formation of acid rain has negative impacts on the environment, such as on forests and marine ecosystems. (Streets et al., 1997). 
  3. Formation of ozone (O3) and fine particulate matter (e.g. PM2.5)— through the oxidation of SO2 and the formation and production of SO4 particles, degrading air quality and rendering subsequent negative impacts on human health (Yau et al., 2013). For instance, Lin et al’s (2018) have found emissions from shipping pollution to be positively associated with increased cardiovascular mortality in Guangzhou, China. 

However, while it seems obvious that a reduction in shipping emissions would bring benefits to both the environment, and to human health, a solution that seeks to downsize the shipping industry is not feasible. This is because of the continued reliance on the shipping industry for the transportation of goods and resources around the world. 

Furthermore, the growth of the shipping industry is unlikely to slow down anytime soon. One contributing factor is the increasing retreat of Arctic sea ice, which has increased the prospect of the formation of new transit routes (e.g. Northern Sea Route, Northwest Passage, and Transpolar Sea Route). These would likely result in an increase in shipping activities in the Arctic region in the future (Gong et al., 2018). This is evident in Jing et al’s (2021) projection of CO2 emission from shipping activity in the Arctic, where they have projected CO2 emissions to increase by 1.76 times by 2050, under business as usual (BAU) scenarios. This increase in CO2 emissions would not only aggravate the warming and melting of Arctic sea ice, but the emission of accompanying air pollutants would also negatively harm the surrounding environment. 

References: 

Corbett, J. J., Winebrake, J. J., Green, E. H., Kasibhatla, P., Eyring, V., & Lauer, A. (2007). Mortality from ship emissions: A global assessment. Environmental Science & Technology, 41(24), 8512–8518. https://doi.org/10.1021/es071686z

Eyring, V., Isaksen, I. S. A., Berntsen, T., Collins, W. J., Corbett, J. J., Endresen, O., Grainger, R. G., Moldanova, J., Schlager, H., & Stevenson, D. S. (2010). Transport impacts on atmosphere and climate: Shipping. Atmospheric Environment, 44(37), 4735–4771. https://doi.org/10.1016/j.atmosenv.2009.04.059

Geels, C., Winther, M., Andersson, C., Jalkanen, J.-P., Brandt, J., Frohn, L. M., Im, U., Leung, W., & Christensen, J. H. (2021). Projections of shipping emissions and the related impact on air pollution and human health in the Nordic region. Atmospheric Chemistry and Physics, 21(16), 12495–12519. https://doi.org/10.5194/acp-21-12495-2021

Gong, W., Beagley, S. R., Cousineau, S., Sassi, M., Munoz-Alpizar, R., Ménard, S., Racine, J., Zhang, J., Chen, J., Morrison, H., Sharma, S., Huang, L., Bellavance, P., Ly, J., Izdebski, P., Lyons, L., & Holt, R. (2018). Assessing the impact of shipping emissions on air pollution in the Canadian Arctic and northern regions: Current and future modelled scenarios. Atmospheric Chemistry and Physics, 18(22), 16653–16687. https://doi.org/10.5194/acp-18-16653-2018

Jing, D., Dai, L., Hu, H., Ding, W., Wang, Y., & Zhou, X. (2021). CO2 emission projection for Arctic shipping: A system dynamics approach. Ocean & Coastal Management, 205, 105531. https://doi.org/10.1016/j.ocecoaman.2021.105531

Lin, H., Tao, J., Qian, Z. (Min), Ruan, Z., Xu, Y., Hang, J., Xu, X., Liu, T., Guo, Y., Zeng, W., Xiao, J., Guo, L., Li, X., & Ma, W. (2018). Shipping pollution emission associated with increased cardiovascular mortality: A time series study in Guangzhou, China. Environmental Pollution, 241, 862–868. https://doi.org/10.1016/j.envpol.2018.06.027

Streets, D. G., Carmichael, G. R., & Arndt, R. L. (1997). Sulfur dioxide emissions and sulfur deposition from international shipping in Asian waters. Atmospheric Environment, 31(10), 1573–1582. https://doi.org/10.1016/S1352-2310(96)00204-X

UK Research and Innovation. (2021, August 10). Shipping industry reduces carbon emissions with space technology. UKRI. https://www.ukri.org/news/shipping-industry-reduces-carbon-emissions-with-space-technology/

Viana, M., Hammingh, P., Colette, A., Querol, X., Degraeuwe, B., Vlieger, I. de, & van Aardenne, J. (2014). Impact of maritime transport emissions on coastal air quality in Europe. Atmospheric Environment, 90, 96–105. https://doi.org/10.1016/j.atmosenv.2014.03.046

Yau, P. S., Lee, S. C., Cheng, Y., Huang, Y., Lai, S. C., & Xu, X. H. (2013). Contribution of ship emissions to the fine particulate in the community near an international port in Hong Kong. Atmospheric Research, 124, 61–72. https://doi.org/10.1016/j.atmosres.2012.12.009

Zhang, Y., Yang, X., Brown, R., Yang, L., Morawska, L., Ristovski, Z., Fu, Q., & Huang, C. (2017). Shipping emissions and their impacts on air quality in China. Science of The Total Environment, 581–582, 186–198. https://doi.org/10.1016/j.scitotenv.2016.12.098