Sathish Mohan
Botsa
*,
Tara
DLLM
,
N. S.
Magesh
and
Anoop Kumar
Tiwari
*
National Centre for Polar and Ocean Research, Ministry of Earth Sciences, Vasco Da Gama, Goa-403804, India. E-mail: anooptiwari@ncpor.res.in
First published on 31st July 2021
With the advent of industrialization, aerosol pollutants have gained global attention for being a formidable threat to the human health and climate change. These pollutants travel via long range transportation to the far reaches of the Earth, wreaking havoc. Black carbon (BC) depositories have repercussions in snow and ice profiles such as alterations in ablation and albedo processes leading to accelerated ice melting rates. In the present study, atmospheric BC aerosol concentrations were measured at ‘Maitri’, the Indian Polar research station situated in Schirmacher Hills, East Antarctica during the austral summer of December 2018 to February 2019 on behalf of the XXXVIII Indian Scientific Expedition to Antarctica (ISEA). For that, an AE42 Aethalometer was used and found a maximum concentration of 82 ng m−3 for BC aerosol between a timeline of 09.00 and 13.00 LT in the month of February, 2019 whereas a minimum concentration of 37 ng m−3 in the timeline of 21.00–22.00 LT, Dec 2018, with the mean of 60 ng m−3 being observed throughout the study period. The potential source areas (Patagonia, Australia, New Zealand and South Africa) were examined to study the source of long-range transport of BC to Maitri by backward and forward trajectory analyses. The trajectory analysis confirmed that Patagonia is a definitive BC origin in addition to the day-to-day station related activities. The influence of meteorological parameters on BC aerosols at Maitri was also studied and correlation analysis stated that BC has a negative alliance with RH, temperature and pressure except wind speed denoting meteorological conditions as a driver of spatio-temporal variation of BC.
Environmental significanceThis peer-reviewed literature includes black carbon studies and its health effects. This study discusses the atmospheric BC aerosol concentrations measured at ‘Maitri’, the Indian Polar research station in East Antarctica during the austral summer of December 2018 to February 2019 in the part of XXXVIII Indian Scientific Expedition to Antarctica. This study reveals a new path to identify the potential source areas for BC aerosols to the East Antarctica. The authors have not used any hazardous chemicals or substances to assessing air quality and their potential sources. Hence, in support of study on environment and pollution level due to BC aerosols at Antarctica, this work has significance and can contribute some knowledge to science. |
Antarctica is a no-man's land with pristine environment, entirely encompassed by snow and ice. The nominal but gradual pollution of Antarctica is attributed to the rapid increase in anthropogenic activities and tourism. Environmental protection of Antarctica is globally recognized and documented in the Antarctica Treaty.13 The treaty and its corresponding annexure set the guidelines for international responsibilities to save and maintain the mint condition of Antarctica. The Madrid Protocol on Environmental Protection was held to enhance and clarify the treaty's environmental protection practices.14
In the recent past, researchers have reported the presence of BC within Antarctica's environmental matrices.15 Bulk producers steering from long range transportation of BC to Antarctica are surrounding continents of South America, Africa and Australia.16 Short and long-term climate variations could affect the local transport of BC from the biomass burning on Antarctica, within the southern hemisphere. Therefore, a scientific program was designed to study the environmental impact assessment through BC emissions and their sources at the Maitri station during the austral summer period of December 2018 to February 2019 to assess the BC variations and long-range transport predictions via the HYSPLIT trajectory analysis (backward/forward) under the influence of meteorological properties. This work presents the study on the long-term observations that predict the reliable sources of BC to East Antarctica.
Two diesel generators were continually operated at the station, which generated ∼62–120 kVA (maximum) of electricity for maintenance and scientific activities.17 The transportation of goods and personnel to airport and other stations was dependent on the use of diesel powered vehicles. Local activities may have contributed to the air pollution that may have travelled via advection to the Maitri station. Meteorological parameters at the Maitri station were recorded by the Indian Meteorological Department (IMD) using an Automatic Weather Station (AWS, Dynalab Weathertech-WL1002) at an interval of 1 min. This collected data points such as relative humidity (RH), air temperature (T), wind direction (WD), wind speed (WS) and pressure (P) at the Maitri station.
bATN (corrected) = (1 + k × ATN) × bATN (Aethalometer) | (1) |
BC (corrected) = bATN (corrected)/σATN = (1 + k × ATN) × BC (Aethalometer) | (2) |
The potential distant sources were assessed from the backward/forward trajectory analysis with the help of HYSPLIT4 model developed by NOAA's Air Resource Laboratory. The location coordinates were set for 120 hour runs at 6 hour intervals for backward projection and 240 hour runs at 6 hour interval for the forward trajectory analysis. In HYSPLIT settings, the precipitation was enabled and a single trajectory protocol was run for trajectories at three different heights (100, 500 and 1000 m) over the observation period of 19th December 2018 to 20th February 2019 for the identification of trajectory patterns or dispersion variability. Trajectory analysis results were saved as a “.kmz’’ file format with end plot using coordinates of the location. The trajectories were overlaid in one coordinate file using ArcGIS 10.3.
It can be found that the daily mean BC concentration varied from 37 to 82 ng m−3 with a mean of 60 ng m−3 during the observation period. Also, large intra-day variation in the BC concentration was noticed and confirmed by standard deviations, as shown by the vertical bars in Fi. S1 (ESI†). The sampling site was selected as Tirumala Hut, upwind from the station distanced around 300 meters away from the power generators and about 100 m from the electrical incinerators. The obtained BC concentrations exhibit variability as weak and strong based on a 100 ng m−3 benchmark, above which reflected a robust-local influence.24 Remarkably, the observed concentrations were mostly weak (73%), suggesting that the regional impact is dominant. The mean BC concentration (<60 ng m−3) fell under 59.8% of total BC. Although, the higher concentrations were recorded amidst high wind owing to ablation of snow and its BC scavenging ability acting as a long-range transport barrier of BC from the other continents.17
High mean BC concentration (82 ng m−3) was observed throughout the monitoring period due to emissions; direct influence of local emissions from the local station combustion activities are associated with winds emanating from the direction of the station, which result in high mean value. The BC flux calculated as a product of wind speed and BC concentration showed a clear directionality.24 BC emission from anthropogenic activities at each station is likely to be negligible or very low in BC source strength in other regions in Antarctic. It was hypothesized that the BC point sources originated from beyond the Antarctic Circle as no proximal source was strong enough to maintain ambient BC concentrations within the area of interest. In other words, BC can be used as a tracer of long-range transport of aerosols to Antarctic regions. Moreover, other sources of BC at any Antarctic station could be emissions from the nearby research stations.17
The average BC mass concentration measured at Maitri is different from various sites in Antarctica (Table 1), which is attributed to the accumulation of BC aerosols from regional, local anthropogenic activities at the station and distant repositories.25,26Table 1 represents the comparison of the BC concentration at the present site with other sites reported in Antarctica. In an earlier study, our group had reported Maitri station BC concentration to be 75 ng m−3, which was now increased to 82 ng m−3 due to the variations of the movement of air parcels with time infused by local and global activities. However, day-average of the BC aerosols are highest in February (63.4 ± 11 ng m−3), followed by January (56.6 ± 12.4 ng m−3) and December (51.6 ± 6.8 ng m−3). Even though the scope of this comparison is narrow, it encapsulates the nature of contrast in the BC concentrations in diverse environments across Antarctica. Copious stations reported ambiguous BC concentrations due to the choice of fuel based tasks.27,28
Sampling Site | Lat/long | Elevation (m.s.l) or(a.s.l) | Study period (Year) | Approx. BC concentration (ng m−3) | References |
---|---|---|---|---|---|
McMurdo station | 77°51′S, 166°41′E | — | 1995–1996 | 300 | 24 |
Larsemann Hills of coastal Antarctic (Bharati) | 69.73°S, 76.19°E | 48 m (msl) | January–March 2009 | 13 | 17 |
Maitri | 70.77°S, 11.73°E | 123 m (msl) | 75 | ||
Halley station | 75 35′S, 26 14′W | — | February 1992–1995 | 0.3–2 (mean) | 29 |
Neumayer station | 70°39′S, 8°15′W | — | 1999–2009 | 2.6 | 30 |
2006–2022 | |||||
Ferraz, King George Island | 62°05′S, 58°23.5′W | — | 1993, 1997, 1998 | 8.3 | 31 |
Maitri | 70.77°S, 11.73°E | 123 m (msl) | Dec 2018–Feb 2019 | 37–82 (mean 60) | Current study |
Fig. 3a shows the backward trajectory to determine the BC source range variation and signifies the degree of impact on the long range transport. BC transport is different with great variation in the source range of the air-mass particulate backward trajectory. The yellow circle represents the sampling location at the Maitri station. An ice-sheet in Antarctica occupies a large surface area with different multiple altitudes. In Antarctica, the elevation ranges from 3500 m (asl) to a few meters in coastal regions.33 Accordingly, the selected initial point is calculated as air parcel heights from ground level. Hence, the studies on aerosol parcels crossing at 100 (red), 500 (blue) and 1000 m (green) of agl were conducted in this study and compared with the aerosol transport at the observatory site five days prior. The results revealed that the BC aerosol transportation is mainly of oceanic origin perhaps because of the high altitude and elevated precipitation levels, therefore resulting in variability in the BC concentrations during the summer time.34
Fig. 3 (a) Back-trajectory analysis for the source of BC to the observatory site. (b) Forward trajectory analysis of PSA sources for BC sources. |
On the other hand, a unique maximum BC aerosol concentration was observed during the window of 22–26 January 2019. This discrepancy was explained by the HYSPLIT forward analysis in which ten days forward trajectories were employed at the height of 100 m, 500 m and 1000 m agl. A primary input of Antarctic dust deposition was estimated from two dominant potential source areas (PSAs) namely Australia and southern South America.35,36 Neff and Bertler (2015) have reported that four PSAs, which contributed more BC to Antarctica.
They are (i) Patagonia: 44° S, 67° W, (ii) Australia: 29° S, 137.5° E, (iii) New Zealand: 43.5° S, 172° E and (iv) South Africa: 28° S, 21° E. Fig. 3b displays the weighed ten-day forward trajectory for the above four PSAs and confirmed that the source of BC aerosols for the study area is Patagonia at 100 m agl for the observed maximum BC concentration period. Thereafter, ten days forward trajectories were initiated from Patagonia, which contributed 15.5% of BC to the station (Fig. S2 in ESI†) in two sets of days (6 Jan 2019 and 26 Jan 2019) during the observatory period (19th December 2018 to 20th February 2019) due to proximity and efficient transport. These air parcels ultimately get incorporated into the Antarctic Circumpolar Vortex (ACV) before mass compensation by the anticyclonic polar easterlies in the East Antarctic region.37
Fig. 4 (i) Diurnal variations of (a) temperature, (b) RH, (c) pressure and (d) wind speed at station. (ii) Correlation of the BC concentration with pressure, temperature, RH and wind speed. |
Fig. 4i(b) illustrates the RH mean values for the observational period at Maitri, indicating that the minimum and maximum percentages of humidity were 37.3 and 80.4, respectively, with an average of 53.1 ± 10.7%. The BC aerosol concentration is also strongly influenced by wind speed and direction. The wind speed exhibits a better correlation with the BC mass, as depicted in Fig. 4ii. The sampling location was upwind, and the dominant wind direction over Maitri was Southwestern (SW), and the prevailing wind speed was 18–20 m s−1, as shown in Fig. 4i(d). A lower wind speed (4.12 m s−1) and low BC mass (42 ng m−3) were observed on 14th January, 2019, whereas the highest wind speed (27.7 m s−1) with an average concentration of 13.5 ± 5.9 (BC was 37 ng m−3) was recorded on 10th February, 2019 and the reason could be due to the sample inlet placement in the upwind direction.
In context to experimental cross-contamination from local point sources, placement in the upwind direction was taken into consideration to prevent emissions from the station-related activities. Although during calm conditions or change in wind direction, the short term contamination stood far above the normal values. Fig. S3 in ESI† implies the comparison of BC with (a) wind speed, (b) temperature, (c) RH and (d) pressure; among all, good trend occurred with the wind speed.
Footnote |
† Electronic supplementary information (ESI) available. See DOI: 10.1039/d1ea00024a |
This journal is © The Royal Society of Chemistry 2021 |