A Mid-Tier Approach to Estimating Durban’s Port Marine Mobile Emissions: Gauging Air Quality Impacts in South Durban
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe authors have used AEROMOD to model air quality in Durban's port. They have used mid-tier activity based approach to model the emissions. For the most part the presentation is good. I would like to see that authors explain AEROMOD modeling part well.
1. what are the units of the emissions given in table 1.
2. The authors have give details of AEROMOD sir dispersion model used.
3. Did the authors consider the emission from the OGV as moving source?
4. Meteorological data inputted into the AEROMOD has to explain in gist
5. At what height the annual pollutant plotted in figure 6-9?
6. why are the annual SO2 and NO2 look different qualitatively?
Author Response
- COMMENT 1: what are the units of the emissions given in table 1.
RESPONSE 1: Page 9, Line 386: Expression of Unit of Measurements in Table 1 was changed from the abbreviated “tpy” to “tonnes per year”
- COMMENT 2: The authors have give details of AEROMOD sir dispersion model used.
RESPONSE 2: Page 11, Line 407: The following explanation about AERMOD modelling existed: “AERMOD air dispersion model was used to map the ambient concentration and spatial distribution of pollutants of NO2, SO2, PM10, and HC. The AERMOD uses meteorological data, emissions data, and the terrain data to map the density and the spatial concentration of pollutants in space. A CALPUFF ready PSU/NCAR MM5 (prognostic mesoscale weather model) meteorological file from Lakes Environmental was used to produce meteorology inputs for AERMOD for the GPS coordinates at the centre of Durban Port for the year in focus, 2018.”
- COMMENT 3: Did the authors consider the emission from the OGV as moving source?
RESPONSE 3: YES, the OGVs were considered as moving sources when the calculations of emissions were made. However, As AERMOD models the sources of pollutants as either point, line, or area sources, the location where ships produced their pollutants were regarded as line sources of pollution as the ships travelled along those routes.
- COMMENT 4: Meteorological data inputted into the AEROMOD has to explain in gist
RESPONSE 4: Page 11, Line 414: The following paragraph has been added: “The meteorological data used in AERMOD can be obtained from the lakes environmental (Lakes Software, 2024). The stack height inserted on AERMOD was 30 metres above sea level and the flue gas emission rate estimated to be 30 meters per second (m/s) with the temperature of 350 á´¼C for all ships. The roughness parameters were set at 0.3 metres and mostly urban (Saxe and Larson, 2004).”
The following two sources were added to the list of references:
Page 17, Line 594: Lakes Software. (2024). Order Met Data. Online: Available https://www.weblakes.com/met-data/order-met-data/ [Accessed 29 September 2024].
Page 18, Line 612: Saxe, H. and Larsen, T. (2004). Air pollution from ships in three Danish ports. Atmospheric Environment, 38, 4057-4067.
- COMMENT 5: At what height the annual pollutant plotted in figure 6-9?
RESPONSE 5: Page 11, Line 414: The following paragraph has been added after : “The meteorological data used in AERMOD can be obtained from the lakes environmental (Lakes Software, 2024). The stack height inserted on AERMOD was 30 metres above sea level and the flue gas emission rate estimated to be 30 meters per second (m/s) with the temperature of 350 á´¼C for all ships. The roughness parameters were set at 0.3 metres and mostly urban (Saxe and Larson, 2004).”
- COMMENT 6: why are the annual SO2 and NO2 look different qualitatively?
RESPONSE 6: We agree that this is an interesting observation. However, this is what the AERMOD results produced after the SO2 and the NO2 were modelled. It may be because their dispersion for the same meteorological conditions is different because of their properties.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsThe authors present a study of estimating the emission from ships in the Durban Port of South Africa for the year 2018. Emission from shipping, which not only affects greenhouse gases but also pollutants that affect air quality such as in seaports, is a growing concern. This is a welcome study on shipping emission as part of a emission inventory of a coastal city.
The authors used mid-tier approach (between top-down approach using fuel consumption and detaiingl each vessel emission) based on average of all vessel characteristics. The method is presented clearly and the results of emission of NOx, SO2, PM10, HC are estimated. Modelling using AERMOD was also carried out to determine the spatial distribution of these pollutnats over the port and its vicinities. The annual average ambient concentration of these pollutants are within the permissible air quality sandards of South Africa. SO2 maximum is briefly higher than the maximum allowable standard. My concern is the use of AERMOD which does not have chemiscal transport module to account for the formation of secondary inorganic aerosols (SIA) and secondary organic aerosols (SOA) unlike WRF-Chem which has chemistry mechanism. Do the authors account for onshore emission due to shipping-related activities such as power supplying to ships at berths ?
Overall, I recommend the manuscript to have minor revision before being accepted for publication.
Other minor comments:
(1) Line 72: tons not teu
(2) Figure 1 is difficult to read the legends and labels. Better resolution is required.
Author Response
- COMMENT 1: Line 72: tons not teu
RESPONSE 1: The “teu” used in this sentence stands for “twenty-foot equivalent units”. This sentence therefore has been rephrased to read “The Durban Port is the busiest port in Sub-Saharan Africa in terms of volume of containers passing through the port each year and the third busiest in Africa (after Tanger Med in Morocco and Port Said in Egypt) with container throughput of approximately 3 million twenty-foot equivalent unit (teu) per annum (Larnyoh, 2020; Lloyd’s List Intelligence, 2020).”
- COMMENT 2: Figure 1 is difficult to read the legends and labels. Better resolution is required.
RESPONSE 2: The small size of Figure 1 makes the legends and labels harder to read. However, when the size is expanded, the readability of the legends and labels improves and zooming-in makes the pictures to be much clearer. The picture size has therefore been slightly increased to improve clarity and readability.
Author Response File: Author Response.pdf
