Diverse changes in shipping emissions around the Western Pacific ports under the coeffect of the epidemic and fuel oil policy.

The Western Pacific Ocean (the WPO), as one of the busiest shipping areas in the world, holds a complex water traffic network. In 2020, the International Maritime Organization (IMO) low-sulfur fuel regulations were implemented globally, while the COVID-19 outbreak influenced shipping activities together. This study aimed to assess the combined impact of epidemics and low-sulfur fuel policies on ship emissions, as well as their environmental effects on the WPO. The ship emission model based on the Automatic Identification System (AIS) data was applied to analyze the monthly emission variations during 2018-2020. It was found that the epidemic had obvious diverse influences on the coastal ports in the WPO. Overall, shipping emissions declined by 15 %-30 % in the first half of 2020 compared with those in 2019 due to the COVID-19 lockdown, whereas they rebounded in the second half as a result of trade recovery. The pollutants discharged per unit of cargo by ships rose after the large-range lockdown. China's multiphase domestic emission control areas (DECAs) and the IMO global low-sulfur fuel regulation have greatly reduced SO2 emissions from ships and caused them to "bypass and come back" to save fuel costs around emission control areas from 2018 to 2020. Based on satellite data and land-based measurements, it was found that the air quality over sea water and coastal cities has shown a positive response to changes in ship-emitted NOx and SO2. Our results reveal that changes in shipping emissions during typical periods, depending on their niches in the complex port traffic network, call for further efforts for cleaner fuel oils, optimized ECA and ship lane coordination in the future. Shipping related air pollutions during the later economic recovery also needs to be addressed after international scale standing-by events.

Impact of air emissions from shipping on marine phytoplankton growth.

With the rapid expansion of maritime traffic, increases in air emissions from shipping have exacerbated numerous environmental issues, including air pollution and climate change. However, the effects of such emissions on marine biogeochemistry remain poorly understood. Here, we collected ship-emitted particles (SEPs) from the stack of a heavy-oil-powered vessel using an onboard emission test system and investigated the impact of SEPs on phytoplankton growth over the northwest Pacific Ocean (NWPO). In SEP microcosm experiments conducted in oceanic zones with different trophic statuses, the phytoplankton response, as indicated by chlorophyll a (Chl a), has been shown to increase with the proportion of SEP-derived nitrogen (N) relative to N stocks (PSN) in baseline seawater, suggesting that SEPs generally promote phytoplankton growth via N fertilisation. Simulations using an air quality model combined with a ship emission inventory further showed that oxidised N (NOx) emissions from shipping contributed ~43% of the atmospheric N deposition flux in the NWPO. Air emissions from shipping (e.g. NOx and sulphur dioxide) also indirectly enhanced the deposition of reduced N that existed in the atmosphere, constituting ~15% of the atmospheric N deposition flux. These results suggest that the impact of airborne ship emissions on atmospheric N deposition is comparable to that of land-based emissions in the NWPO. Based on the ship-induced PSN in surface seawater calculated by modeling results and World Ocean Atlas 2013 nutrient dataset, and the well-established quantitative relationship between Chl a and PSN obtained from microcosm experiments, we found a noticeable change in surface Chl a concentrations due to N deposition derived from marine traffic in the NWPO, particularly in the coastal waters of the Yellow Sea and open oceans. This work attempts to establish a direct link between marine productivity and air emissions from shipping.

Modeling the impact of marine DMS emissions on summertime air quality over the coastal East China Seas.

[1] Biogenic emission of dimethyl sulfide (DMS) from seawater is the major natural source of sulfur into the atmosphere. In this study, we use an advanced air quality model (CMAQv5.2) with DMS chemistry to examine the impact of DMS emissions from seawater on summertime air quality over China. A national scale database of DMS concentration in seawater is established based on a five-year observational record in the East China seas including the Bohai Sea, the Yellow Sea and the East China Sea. We employ a commonly used global database and also the newly developed local database of oceanic DMS concentration, calculate DMS emissions using three different parameterization schemes, and perform five different model simulations for July, 2018. Results indicate that in large coastal areas of China, the average DMS emissions flux obtained with the local database is three times higher than that resulting from the global database, with a mean value of 9.1 µmol m-2 d-1 in the Bohai Sea, 8.4 µmol m-2 d-1 in the Yellow Sea and 13.4 µmol m-2 d-1 in the East China Sea. The total DMS emissions flux calculated with the Nightingale scheme is 42% higher than that obtained with the Liss and Merlivat scheme, but is 15% lower than that obtained with the Wanninkhof scheme. Among the three parameterizations, results of the Liss and Merlivat scheme agree better with the ship-based observations over China's coastal waters. DMS emissions with the Liss and Merlivat parametrization increase atmospheric sulfur dioxide (SO2) and sulfate (SO4 2-) concentration over the East China seas by 6.4% and 3.3%, respectively. Our results indicate that although the anthropogenic source is still the dominant contributor of atmospheric sulfur burden in China, biogenic DMS emissions source is nonnegligible.

Impact of dimethylsulfide chemistry on air quality over the Northern Hemisphere.

We implement oceanic dimethylsulfide (DMS) emissions and its atmospheric chemical reactions into the Community Multiscale Air Quality (CMAQv53) model and perform annual simulations without and with DMS chemistry to quantify its impact on tropospheric composition and air quality over the Northern Hemisphere. DMS chemistry enhances both sulfur dioxide (SO2) and sulfate ( S O 4 2 - ) over seawater and coastal areas. It enhances annual mean surface SO2 concentration by +46 pptv and S O 4 2 - by +0.33 µg/m3 and decreases aerosol nitrate concentration by -0.07 µg/m3 over seawater compared to the simulation without DMS chemistry. The changes decrease with altitude and are limited to the lower atmosphere. Impacts of DMS chemistry on S O 4 2 - are largest in the summer and lowest in the fall due to the seasonality of DMS emissions, atmospheric photochemistry and resultant oxidant levels. Hydroxyl and nitrate radical-initiated pathways oxidize 75% of the DMS while halogen-initiated pathways oxidize 25%. DMS chemistry leads to more acidic particles over seawater by decreasing aerosol pH. Increased S O 4 2 - from DMS enhances atmospheric extinction while lower aerosol nitrate reduces the extinction so that the net effect of DMS chemistry on visibility tends to remain unchanged over most of the seawater.

Regional and Urban-Scale Environmental Influences of Oceanic DMS Emissions over Coastal China Seas.

Marine biogenic dimethyl sulfide (DMS) is an important natural source of sulfur in the atmosphere, which may play an important role in air quality. In this study, the WRF-CMAQ model is employed to assess the impact of DMS on the atmospheric environment at the regional scale of eastern coastal China and urban scale of Shanghai in 2017. A national scale database of DMS concentration in seawater is established based on the historical DMS measurements in the Yellow Sea, the Bohai Sea and the East China Sea in different seasons during 2009~2017. Results indicate that the sea-to-air emission flux of DMS varies greatly in different seasons, with the highest in summer, followed by spring and autumn, and the lowest in winter. The annual DMS emissions from the Yellow Sea, the Bohai Sea and the East China Sea are 0.008, 0.059, and 0.15 Tg S a-1, respectively. At the regional scale, DMS emissions increase atmospheric sulfur dioxide (SO2) and sulfate ( SO 4 2 - ) concentrations over the East China seas by a maximum of 8% in summer and a minimum of 2% in winter, respectively. At the urban scale, the addition of DMS emissions increase the SO2 and SO 4 2 - levels by 2% and 5%, respectively, and reduce ozone (O3) in the air of Shanghai by 1.5%~2.5%. DMS emissions increase fine-mode ammonium particle concentration distribution by 4% and 5%, and fine-mode nss- SO 4 2 - concentration distributions by 4% and 9% in the urban and marine air, respectively. Our results indicate that although anthropogenic sources are still the dominant contributor of atmospheric sulfur burden in China, biogenic DMS emissions source cannot be ignored.

Cool Roof and Green Roof Adoption in a Metropolitan Area: Climate Impacts during Summer and Winter.

This study, for the first time, estimates the climate impacts of adopting green roofs and cool roofs on the seasonal urban climate of 16 cities that comprise the Yangtze River Delta metropolitan. We use a suite of regional climate simulation to compare the local climate impacts of the implementation of different roof strategies in summer and winter. The results indicate that in summer, the 2 m surface temperature reduced significantly when these two roof strategies are adopted, with peak reductions of 0.74 and 1.19 K for green roofs and cool roofs, respectively. The cooling impact of cool roofs is more effective than that of green roofs under the scenarios assumed in this study. Besides, rooted in the different mechanisms influencing urban heat flux, significant indirect effects were also observed: adopting cool roofs leads to a decreased precipitation in summer and an apparent reduction in wintertime temperatures in the urban area. Although cool roofs can be an effective way to reduce high temperatures during the summer, green roofs have fewer adverse impacts on other climate conditions. These results underline the need for comprehensive climate change policies that incorporate place-based solutions and extend beyond the nearly exclusive focus on summertime cooling.

Increasing surface ozone and enhanced secondary organic carbon formation at a city junction site: An epitome of the Yangtze River Delta, China (2014-2017).

This study aims to understand the characteristics of surface ozone (O3), search for factors affecting the variations in its concentration, and estimate its impacts on the secondary organic carbon (SOC) levels and atmospheric oxidation capacities in the Yangtze River Delta (YRD). Four years of continuous observations (2014-2017) of the surface O3, organic carbon, elemental carbon, nitrogen oxides, PM2.5 and meteorological factors along with three years of measurements (2015-2017) of the concentrations of 56 volatile organic compounds were conducted at a rural site. Our measurements showed that the total number of O3 pollution days more than doubled over the four-year period, from 28 days in 2014 to 76 days in 2017. The annual mean of the maximum daily 8-h average O3 concentration during the months with the strongest solar radiation (July-September) showed a 6.8% growth rate, from 124.5 (2014) to 149.8 µg m-3 (2017). Regional transport was shown to be the dominant contributor to the high level of O3 based on a process analysis of the O3 variation using the Weather Research and Forecasting-Community Multiscale Air Quality model for this site. The simulation results indicated that the city junction site served well as an epitome of the regional background of the YRD. We also found that the level of SOC, which is a major component of PM2.5 that results from atmospheric oxidizing processes, gradually increased with the increase in the surface O3 level, even though the overall PM2.5 concentration significantly decreased each year. There was an increasingly strong correlation between SOC and Ox (O3 + nitrogen dioxide) during both the daytime and night-time from 2014 to 2017 when the highest annual O3 concentration was observed. These findings imply that the atmospheric oxidation capacity increased and likely contributed to the SOC production in the YRD during 2014-2017.

Projection of ship emissions and their impact on air quality in 2030 in Yangtze River delta, China.

China has been in the implementation phase of Domestic Ship Emission Control Areas (DECAs) regulation to reduce emissions of air pollutants from ships near populated areas since 2016. The Yangtze River Delta (YRD) is one of the busiest port clusters in the world, accounting for 11% of global seaborne cargo throughput, so future improvements in shipping emission controls may still be important in this region. To assess the impact of future ship emissions on air quality of coastal areas, this study evaluates emissions reductions and air quality in 2030 for three scenarios (business as usual, stricter regulations, and aspirational policies) representing increasing levels of control compared with a base year of 2015. We projected ship emissions in the region using a bottom-up approach developed in this study and based on the historical ship automatic identification system (AIS) activity data. We then predicted air quality across the YRD region in 2030 using the Community Multiscale Air Quality (CMAQ) model. The annual average contributions of ship emissions to ambient PM2.5 would decrease by 70.9%, 80.4%, and 86.2% relative to 2015 under the three scenarios, with the largest reductions of more than 4.1 µg/m3 near Shanghai Port under the aspirational scenario. Reductions in ship emissions generally led to lower levels of PM2.5, particularly in most of the coastal cities in the YRD. Compared with a business-as-usual approach the aspirational scenario reduced SO2, NOx and PM2.5 concentrations from shipping by 71.8%, 61.1% and 52.5%, respectively. It was also more effective than the stricter regulation scenario, suggesting that the requirement to use 0.1% sulfur fuel within a 100Nm DECA would have additional benefits to ambient PM2.5 concentrations beyond 12Nm DECA area. This study provides evidence to inform deliberations on the potential air quality benefits of future control policies for ship emissions in China.

Changes in the SO2 Level and PM2.5 Components in Shanghai Driven by Implementing the Ship Emission Control Policy.

This study aims to understand the effect of the Domestic Emission Control Area (DECA) policy on ambient SO2 and particle components in Shanghai. Online single particle analysis and SO2 measurements from 2015 to 2017 were compared to analyze the long-term variations before and after the DECA policy. Our study showed that there was a significant decrease in SO2 by 27-55% after the implementation of the DECA policy. The number fraction of ship-emitted particles increased along with the increase in ship traffic activity, but the particles tended to contain lower-vanadium content. The elemental carbon component decreased, while the organic carbon components increased after switching oil. One thousand and ninety four ship fuel oil samples were collected. The oil sample analysis confirmed the ambient particle results; sulfur content decreased in domestic ship heavy fuel oils from 2013 to 2018; in the low sulfur fuel oils used after the DECA policy, vanadium was still highly correlated with sulfur as it was in high-sulfur fuels. Our results suggested that heavy fuel oil is still a major part of the low-sulfur ship oils in use. The multiple-component control including organic pollutants regarding low sulfur fuel oils may be necessary for preventing air pollution from ship emissions.