Assessing the PM2.5 impact of biomass combustion in megacity Dhaka, Bangladesh

doi:10.1016/j.envpol.2020.114798

Environmental Pollution

Volume 264, September 2020, 114798

https://doi.org/10.1016/j.envpol.2020.114798 Get rights and content

Highlights

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A biomass burning index was derived using potassium (K).
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A fossil fuel index was developed using sulfur (S).
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Biomass associated PM_2.5 and fossil-fuel associated PM_2.5 were estimated.
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Monsoon air pollution was dominated by the local fossil-fuel associated PM_2.5.
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During non-monsoon time both local and transported crop burning aerosol.

Abstract

In Dhaka, Bangladesh, fine particulate matter (PM_2.5) air pollution shows strong seasonal trends, with significantly higher mean concentrations during winter than during the monsoon (winter = 178.1 μg/m³ vs. monsoon = 30.2 μg/m³). Large-scale open burning of post-harvest agricultural waste across the Indo-Gangetic Plain is a major source of PM_2.5 air pollution in northern India during the non-monsoon period. This study evaluates the extent to which the seasonal differences in PM_2.5 pollution concentrations in Dhaka are accounted for by biomass-burning vs. fossil-fuel combustion sources. To assess this, an index was developed based on elemental potassium (K) as a marker for biomass particulate matter, after adjusting for soil-associated K contributions. Alternatively, particulate sulfur was employed as a tracer index for fossil-fuel combustion PM_2.5. By simultaneously regressing total PM_2.5 on S and adjusted K, the PM_2.5 mass for each day was apportioned into: 1) fossil-fuels combustion associated PM_2.5; 2) biomass-burning associated PM_2.5; and, 3) all other PM_2.5. The results indicated that fossil-fuel combustion contributed 21.6% (19.5 μg/m³), while biomass contributed 40.2% (36.3 μg/m³) of overall average PM_2.5 from September 2013 to December 2017. However, the mean source contributions varied by season: PM_2.5 in Dhaka during the monsoon season was dominated by fossil-fuels sources (44.3%), whereas PM_2.5 mass was dominated by biomass-burning (41.4%) during the remainder of the year. The contribution to PM_2.5 and each of its source components by transport of pollution into Dhaka during non-monsoon time was also evaluated by: 1) Conditional bivariate (CBPF) and pollution rose plots; 2) Concentration weighted trajectories (CWT), and; 3) NASA satellite photos to identify aerosol loading and fire locations on high pollution days. The collective evidence indicates that, while the air pollution in Dhaka is contributed to by both local and transboundary sources, the highest pollution days were dominated by biomass-related PM_2.5, during periods of crop-burning in the Indo-Gangetic Plain.

Graphical abstract

Introduction

Ambient air pollution is a complex mixture, originating from both local and distant sources that vary over time. In addition, air pollution concentrations vary substantially across cities in the world, based on their respective geographic locations and dominant pollutant sources (Li et al., 2019). According to a recent Health Effect Institute (HEI) report, the highest population-weighted pollution concentrations are in North Africa and the Middle East, mainly due to windblown dust, followed by South Asia (especially in northern India and Bangladesh) resulting from various combustion sources, including solid fuel burning (coal and biomass), coal-fired power plants, open agricultural crop burning, traffic, and industries (HEI, 2017).

The megacity Dhaka has been ranked as the 2nd most polluted capital city in the world, with a mean fine particulate matter (aerodynamic diameter of particles ≤2.5 μm, PM_2.5) concentration of 97.1 μg/m³ (AirVisual, 2018). The PM_2.5 concentration in Dhaka has a strong seasonal trend, averaging 175 μg/m³ during winter, but only 32 μg/m³ during the summertime monsoon season (Rahman et al., 2018; Mahmood et al., 2019). The weather in Dhaka is dominated by a rainy monsoon in summer, and a dry season in winter. The rainy monsoon plays an important role in shifting seasonal sources of air pollution. For example, coal-burning brick kilns are a major local air pollution sources in Dhaka (Begum et al., 2014; Begum and Hopke, 2019), with some 1000 brick kilns spread across the Dhaka metro region (Guttikunda et al., 2013), but these kilns only operate only during the dry seasons.

Dhaka is located at northeast end of the Indo-Gangetic Plain (IGP). Emissions from open agricultural-waste burning in the Indo-Gangetic Plain are a dominant source of atmospheric PM_2.5 in northern India during November–April (Bikkina et al., 2019; Rajput et al., 2014). These emissions often contribute to visible haze in this region during winter (Dec–Feb). Prior studies reported that dust and agricultural waste burning particles can travel over 1000 km distance (Lall and Thurston, 2006; Niemi et al., 2009; Uranishi et al., 2019). So, the pollution emitted in the IGP can be transported to Dhaka by prevailing westerly winds. This study investigates the extent to which there is an influence of crop-burning pollution in Dhaka during the non-monsoon period of the year.

In this work, we develop and evaluate seasonal concentrations and back-wind trajectories of sulfur-related PM_2.5 and adjusted potassium-related PM_2.5 in Dhaka, which are used, respectively, as tracers for fossil fuel combustion (e.g., from diesel vehicles and coal burning) and biomass-burning (e.g., from rural household cooking and agricultural crop burning) PM_2.5 air pollution. Such an assessment of the contribution of biomass burning versus fossil-fuel combustion sources in the PM_2.5 pollution in the south-Asian region is important for planning future pollution controls, and can also be used as inputs to epidemiological evaluations of their relative health toxicities.

Section snippets

Air pollution and meteorology data

Daily 24-hr average fine particulate matter (PM_2.5) air pollution concentration records were procured from the Department of the Environment (DoE, CASE project) in Dhaka, Bangladesh for the period from September 2013 to December 2017. This period was selected because cardiovascular emergency department visits, hospitalizations, and mortality data were available for subsequent health effects analyses using the outputs of this study. PM_2.5 samples (24-hr) were collected twice per week on

Fossil fuel combustion, biomass burning, and other PM_2.5 mass contribution estimates

During the entire study period, the average concentration of PM_2.5 for all days (1582 obs.) was 87.7 ± 69.0 μg/m³, and the subset of gravimetric sampling days (388 obs.) was similar (mean = 90.2 ± 68.0 μg/m³), indicating that the gravimetric sampling days were representative of the full study period (Table 1). A strong seasonal pattern was detected in PM_2.5 mass during the study period, with highest levels during non-monsoon period, and lowest during the monsoon season (mean PM_2.5

Conclusions

The results of this study indicate that air quality in Dhaka is affected by both local and long-range transport pollution sources, but the highest days occur at times when the city is most affected by the transported crop-burning biomass burning pollution. While Dhaka air pollution is dominated by local sources during lower pollution days, the peak PM_2.5 pollution days in Dhaka were greatly influenced by transboundary biomass burning pollution from the IGP, Himalayan basin, and Nepal.

These

CRediT authorship contribution statement

Md Mostafijur Rahman: Conceptualization, Data curation, Methodology, Formal analysis, Software, Writing - original draft, Writing - review & editing. Bilkis A. Begum: Writing - review & editing. Philip K. Hopke: Methodology, Writing - review & editing. Kamrun Nahar: Data curation, Writing - review & editing. George D. Thurston: Conceptualization, Methodology, Writing - review & editing, Supervision.

Declaration of competing interest

We have no conflicts of interest to disclose.

Acknowledgement

This work was supported in part by the New York University National Institute of Environmental Health Sciences (NIEHS) Center Grant (ES00260). We gratefully acknowledge Department of Environment, Bangladesh, especially CASE project team for providing the air pollution data.

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^☆: This paper has been recommended for acceptance by Pavlos Kassomenos.

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Assessing the PM2.5 impact of biomass combustion in megacity Dhaka, Bangladesh☆

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Air pollution and meteorology data

Fossil fuel combustion, biomass burning, and other PM2.5 mass contribution estimates

Conclusions

CRediT authorship contribution statement

Declaration of competing interest

Acknowledgement

Atmos. Environ.

Chemometr. Intell. Lab. Syst.

Atmos. Environ.

Atmos. Environ.

Atmos. Environ.

Atmos. Pollut. Res.

Atmos. Environ.

Atmos. Environ.

Sci. Total Environ.

Atmos. Environ.

Environ. Pollut.

Environ. Model. Software

Chemosphere

2018 World Air Quality Report Region & City PM2.5

Chemical and optical characterization of aerosols measured in spring 2002 at the ACE-Asia supersite, Zhenbeitai, China

J. Geophys. Res. Atmos.

Long-range transport of mineral dust to the northeast Indian Ocean: regional versus remote sources and the implications

J. Clim.

Air Quality Status and Trends: 2013-2015

Identification of sources from chemical characterization of fine particulate matter and assessment of ambient air quality in Dhaka, Bangladesh

Aerosol Air Qual. Res.

Identification and apportionment of sources from air particulate matter at urban environments in Bangladesh

Br. J. Appl. Sci. Technol.

Crop residue burning in India: policy challenges and potential solutions

Int. J. Environ. Res. Publ. Health

Atmospheric transport of mineral dust from the Indo-Gangetic Plain: temporal variability, acid processing, and iron solubility

Geochem. Geophys. Geosyst. Res.

Air quality in megacity Delhi affected by countryside biomass burning

Nat. Sustain.

Transboundary atmospheric pollution in Southeast Asia: current methods, limitations and future developments

Crit. Rev. Environ. Sci. Technol.

Synergistic effect in absorption properties of brown carbon and elemental carbon over IGP during weak south-west monsoon

Aerosol Sci. Eng.

Influences of winter haze on fog/low cloud over the Indo-Gangetic plains

J. Geophys. Res. Atmos.

Brown clouds over south Asia: biomass or fossil fuel combustion?

Science

Particulate pollution from brick kiln clusters in the Greater Dhaka region, Bangladesh

Air Qual. Atmos. Health

Assessing the PM_2.5 impact of biomass combustion in megacity Dhaka, Bangladesh☆

Fossil fuel combustion, biomass burning, and other PM_2.5 mass contribution estimates