Ammonia: A Trend of Dry Deposition in Vietnam

Abstract

This research used the calculating method of dry deposition to estimate ammonia (NH₃) dry deposition value and evaluate its trend in 5 recent years. The results indicate that NH₃ concentration is from 1.5 to 11ppb and sites in Southern Vietnam have higher NH₃ gas concentration than Northern Vietnam. The high emitted concentration in September is at the Can Tho site in 2019 and in March at the Ha Noi site in 2023. The 2021 year has the highest NH₃ dry deposition with 35.59 kg/ha/ year and the 2023 year has the lowest NH₃ dry deposition with 24.4 kg/ha/year. Hoa Binh site has the highest NH₃ dry deposition and a strong increase in December 2021. The Can Tho site has high NH₃ dry deposition in most of the years from 2019 to 2023. The rural site reveals higher NH₃ dry deposition than other sites due to agricultural activities. Medium NH₃ dry deposition in 2021 is higher than other years with the biggest gap between years of NH₃ dry deposition. The decreasing trend of NH₃ dry deposition occurred from 1999 to 2023 and there is a strong increase in 2021, then it is sharp decrease to 2023. The decreasing trend reveals a perfect signal for improving environmental quality in good monitoring with NH₃ dry deposition.

Introduction

Ammonia (NH₃) is the most abundant alkaline gas in the atmosphere and it is a major component of total reactive nitrogen [1]. Atmosphere NH₃ is mainly derived from agricultural production processes, including fertilizer application in farming and animal waste emissions in animal husbandry [2], which contribute 80%-90% of total NH₃ emissions [1]. Other sources of NH₃ include industrial processes, vehicular emissions, and volatilization from soils and oceans [1]. Increasing NH₃ emissions have a negative influence on the environment, public health, and climate change. Atmospheric deposition contributes significant amounts of nutrients and polluting compounds to natural ecosystems [3].

Atmospheric deposition is one of the serious environmental pollution issues because it is formed in polluted atmospheric conditions due to excessive gas emissions from waste sources. Deposition includes wet and dry deposition, in which wet deposition is collected through rainwater and dry deposition is drawn from the air via monitoring stations. The dry deposition process controls the transfer of pollutants from the atmosphere to the surface [4]. In the dry deposition, substances exist in the gas form or dust particles and they are blown by the wind, then fall to the ground, the trees, and enter the river system. Dry deposition depends so much on wind speed, temperature, humidity, solar radiation, precipitation amount, and cloud cover factors. Dry deposition of N-compounds includes particulate ammonium (NH+₄) and nitrate (NO−₃) and the gaseous compounds: ammonia (NH₃), nitric acid (HNO₃), nitrogen dioxide (NO₂), nitric oxide (NO), peroxyacetyl nitrate (PAN) and nitrous acid (HNO₂) [3].

Deposition monitoring in the air is one of the basic monitoring items of the Acid Deposition Monitoring Network in East Asia (EANET) [5] which includes 13 countries, including Vietnam. Monitoring stations in Vietnam are covered from the North to South of Vietnam whereas dry deposition monitoring includes 5 stations and is monitored frequently with weekly. Origin data is sent to EANET yearly to store and publish on the EANET website. However, publication data have only each year and it has not been revealed a trend of dry deposition in many recent years. Furthermore, the estimation of dry deposition is calculated by multiplying measured concentrations and deposition velocities [6-8] and only focuses on estimating ammonia dry deposition [9] while research about the trend of ammonia dry deposition has not been mentioned yet, especially in many recent years. Therefore, this research estimates ammonia gas dry deposition in 5 recent years and displays the trend of ammonia gas from the 2019-2023 year to understand the changing of ammonia gas dry deposition in 5 years. This research helps planners to develop environmental policies and make plans to reduce gas emissions into the air.

Methodology

Dry acid deposition of gases is more dangerous than wet acid deposition because it is blown by the wind directly affecting human health. To manage dry acid deposition and develop environmental policies, monitoring dry acid deposition is very necessary. Therefore, this study uses the model-based estimation method to estimate ammonia gas dry deposition combined with aerodynamic resistance, quasi-laminar layer resistance, surface resistance parameters, and meteorological factors such as wind speed, temperature, relative humidity, solar radiation, and precipitation based on equation [10,11] as follows:

$F_i=V_d^i\times C_i$

Whereas:

F_i is the dry deposition of NH₃ gas type

V_d is the deposition velocity of NH₃ gas type

C_i is the atmospheric concentration of NH₃ gas type.

The dry deposition velocity is a function of particle size and wind velocity; the dry deposition velocity increases with decreasing particle diameter in the particle size range of < 0.1 μm. Suitable parameterizations to estimate the deposition velocities of the target species were arranged by Matsuda (2008) [12] fundamentally based on Wesely’s parameterization [11] (Wesely, 1989). The parameterizations were arranged taking into account previous field studies performed in East Asia [12-19]. The fundamental theory of deposition velocity parameterizations was introduced in the texts of Erisman and Draaijers (1995) and Seinfeld and Pandis (1998) [20,21]. From that, deposition velocity Vd is applied by the resistance model [6,22] and considering meteorological factors, deposition surface, and land use [10] to estimate deposition velocity. It is represented by the following equation:

$V_d=\frac{1}{r_a+r_b+r_c}$

Whereas:

V_d is the deposition velocity

R_a is the aerodynamic resistance

R_b is the quasi-laminar layer resistance

R_c is the surface resistance

The R_a and R_b parameters are calculated by the parameterizations of Erisman and Draaijers [20]. R_c is estimated by the equation of Wesely [11] and Smith [23] including stomal parameter, mesophyll, and surface resistance parameters. Data for wind speed, temperature, relative humidity, solar radiation, and precipitation are surveyed at the monitoring stations and used in calculating V_d.

Results and discussion

Total NH₃ gas concentration data are collected from monitoring stations and calculated NH₃ dry deposition for all of Vietnam. The trend of NH₃ dry deposition is presented for 5 years, from 2019 to 2023 year.

Concentration of ammonia gas

NH₃ gas concentration is extracted through monitoring stations from North to South of Vietnam for 5 years and indicates that its concentration is from 1.5 to 11ppb with different years, in which NH₃ gas concentration at the Can Tho site has a higher concentration than other sites while Hoa Binh site has the lowest NH₃ gas concentration, than Ha Noi site. That indicates that the sites in Southern Vietnam have higher NH₃ gas concentration than Northern Vietnam, this significance relates to NH₃ gas emission from the decomposition of animal or plant organic components and fertilizer product manufacturers as well as from vaporing sea water, and stations at the South is near sea than stations at the North. Moreover, changes in NH₃ gas concentration monthly at the Can Tho site in 2019 and 2020 year and at the Ha Noi site in 2021 and 2023 year are clearer than other sites, especially in September 2019 and August 2020 at the Can Tho site; in September 2021 and March 2023 at the Ha Noi site. This change is impacted by climate and weather conditions including temperature, precipitation, wind speed, humidity, etc. When considering the fluctuation of medium NH₃ gas concentration in 5 years present in 2020 is more fluctuating than other years. Thus, NH₃ gas emission at sites is high (the highest is 11ppb), and changing of Southern sites monthly is more than in Northern Vietnam. Higher NH₃ gas emissions were recorded in Southern Vietnam because it is released mainly from agricultural activities while Southern Vietnam is the biggest agricultural production zone in Vietnam (Figure 1).

Figure 1: Changing of NH₃ concentration at stations in Vietnam.

Dry deposition of ammonia gas

According to the calculating equation of dry deposition to estimate NH₃ gas dry deposition, high or low NH₃ gas dry deposition depends significantly on wind speed, temperature, humidity, solar radiation, precipitation amount, and cloud cover factors. The table below indicates that total national NH₃ dry deposition in 5 years was 26.95 kg/ha/2019 year; 26.08 kg/ha/2020 year; 35.59 kg/ha/2021 year; 27.68 kg/ha/2022 year; and 24.4 kg/ha/2023 year. Thus, 2021 year has the highest NH₃ dry deposition and 2023 year has the lowest NH₃ dry deposition in 5 recent years. High or low dry deposition value depends on deposition velocity and gas concentration, in which wind speed; temperature; and precipitation are more affected by dry deposition because climate is more and more drying, with high dry deposition value. Moreover, estimating NH₃ gas dry deposition in each year shows that the Hanoi site has NH₃ dry deposition from 3.43 to 6.97 kg/ha/year in 5 years, in which 2021 year has the highest NH₃ dry deposition and 2023 year has the lowest NH₃ dry deposition. Hoa Binh site presents NH₃ dry deposition from 1.97 - 10.86 kg/ha/year with the highest NH₃ dry deposition in the 2021 year. Ho Chi Minh site has an NH₃ dry deposition value from 4.24 - 5.5 kg/ha/year with a similar NH₃ dry deposition value. Next, the Can Tho site has NH₃ dry deposition from 6.69 - 7.87 kg/ha/year with a small gap of NH₃ dry deposition value each year. However, the NH₃ dry deposition value of the Can Tho site is higher than the Ho Chi Minh site from 2019-2023. The final site is Yen Bai with NH₃ dry deposition value from 5.86 - 7.53 kg/ha/year (Table 1).

Thus, changing of NH₃ dry deposition value at sites monthly reveals the highest NH₃ dry deposition at the Hoa Binh site in 2021 year and higher than other sites. However, the rest of the years at the Hoa Binh site present a very low NH₃ dry deposition value of about 2.2 kg/ha/year lower than other sites. Furthermore, the high NH₃ dry deposition value during 5 years belongs to the Can Tho site with 7.47 kg/ha/year of medium NH₃ dry deposition (Table 1).

Figure 2 reveals clearly Can Tho site with the yellow line has higher NH₃ dry deposition than almost of other sites in years except for 2021 year, while the Hoa Binh site has higher NH₃ dry deposition than other sites in the same year (2021 year). When considering monthly NH₃ dry deposition revealed that high NH₃ dry deposition is from July to September at most of the sites, especially at the Can Tho site. Moreover, Southern and rural sites present normally higher NH₃ dry deposition because NH₃ emission comes from most agricultural activities (Figure 2).

Figure 2: Changing of NH₃ gas dry deposition at stations in Vietnam.

In contrast, urban sites have lower NH₃ dry deposition than Ha Noi and Ho Chi Minh sites. NH₃ dry deposition value in 12 months indicates that it has changed from 0.51 - 1.64 kg/ha/month at the Hoa Binh site and is the highest NH₃ dry deposition, especially in 2021, and strongly increasing in December. NH₃ dry deposition of the Can Tho site ranges from 0.31 - 1.08 kg/ha/month and is the highest NH₃ dry deposition in the 2023 year. Yen Bai site has NH₃ dry deposition from 0.4 - 0.89 kg/ha/month and is the highest NH₃ dry deposition in 1999. Ha Noi site is from 0.26 - 1.08 kg/ha/month of NH₃ dry deposition value and is the second rank after the Hoa Binh site. The last is the Ho Chi Minh site with similar NH₃ dry deposition from 0.2 - 0.71 kg/ha/month. If considering medium NH₃ dry deposition, 2021 year has a higher NH₃ dry deposition value than other years and the biggest gap in changing of NH₃ dry deposition (Figure 2).

Trend of ammonia in 5 years

The figure of NH₃ dry deposition trend in 5 years shows a decreasing trend of NH₃ dry deposition from 1999 to 2023 year. Especially, it is strongly increasing in the 2021 year, and then it is a sharp decrease to the 2023 year. Thus, in general, it is a diminishing trend and with this trend, it predicts that NH₃ dry deposition will decrease gradually in the future for all of Vietnam. The decreasing trend reveals that ammonia gas has been managed well in recent years. This significant trend is a good signal for the environment because NH₃ emission in the air is controlled and monitored well, it will make a fresher atmosphere and helpful with human health (Figure 3).

Figure 3: Trend of NH₃ gas dry deposition in 1999-2023 year.

Conclusion

From determining NH₃ emitted concentration via stations in Vietnam and estimating NH₃ dry deposition amount in sites, this research drew some significant results as: NH₃ concentration is recorded at 1.5 to 11ppb at sites in Southern Vietnam and has higher NH₃ gas concentration than Northern Vietnam. The highest emitted concentration in September is at the Can Tho site in the 2019 year and in March at the Ha Noi site in the 2023 year. The 2021 year has the highest NH₃ dry deposition with 35.59 kg/ha/ year and the 2023 year has the lowest NH₃ dry deposition with 24.4 kg/ha/year. Hoa Binh site has the highest NH₃ dry deposition and a strong increase in December of 2021. The Can Tho site has high NH₃ dry deposition in most of the years from 2019 to 2023 year. The rural site reveals higher NH₃ dry deposition than other sites due to agricultural activities. Medium NH₃ dry deposition in 2021 is higher than other years with the biggest gap between years of NH₃ dry deposition. The decreasing trend of NH₃ dry deposition occurred from 1999 to 2023 year and it had a strong increase in 2021, then a sharp decrease to 2023 year. The decreasing trend reveals a perfect signal for improving environmental quality in good monitoring with NH₃ dry deposition.

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Cite this Article

Nguyen MT. Ammonia: A Trend of Dry Deposition in Vietnam. IgMin Res. January 30, 2025; 3(1): 070-075. IgMin ID: igmin285; DOI:10.61927/igmin285; Available at: igmin.link/p285

• DOI10.61927/igmin285

16 Jan, 2025

Received

29 Jan, 2025

Accepted

30 Jan, 2025

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