Influence of Monsoonal Driving Factors on the Secondary Inorganic Aerosol over Ambient Air in Dhaka

Abstract

Secondary inorganic components significantly contribute to the modification of ambient aerosol properties by forming haze or reducing visibility. This study characterizes the water-soluble components in PM2.5 and explores secondary inorganic aerosol (SIA) over the air in Dhaka, Bangladesh, throughout 2019. PM2.5 samples were collected on a 24 h basis using a high-volume air sampler, and water-soluble inorganic compositions were measured using an ion chromatograph (IC). The observed PM2.5 may pose potential health risks given that their 24 h mean exceeds the ambient air quality guidelines proposed by the World Health Organization (WHO) and the Department of Environment (DoE) of Bangladesh. Among the ions, SO4 2–, Ca2+, and NO3 – were identified as the predominant species that account for 51, 20, and 11% of all soluble components, respectively. The soluble ions in PM2.5 were relatively higher in the summer monsoon (13.26 ± 6.12 μg/m3), possibly due to a combination of rampant anthropogenic activities and the pre-monsoonal meteorology. Humid summer plays a significant role in increasing the amount of SIA through the liquid-phase oxidation of precursor gases. Therefore, scavenging of ions may potentially occur (23% from the overall mean of ions) during the long rainy monsoon season over Dhaka. The anthropogenic origins of PM2.5, such as transportation, industry, and construction dust, are widely present in natural sources all over Dhaka. Dust was more sensitive to enriched PM2.5 than ions from a seawater origin. Excluding winter data, K+ may significantly resuspend from urban dust over Dhaka. The elements and molecular tracer technique reveal that the potential reactive ions (e.g., Cl–, SO4 2–, and NO3 –) were more sensitive to anthropogenic human activities in Dhaka air than to seawater and terrestrial soil. The influence of converting vehicle fleets into compressed natural gas (CNG) run and upgrading kiln technology on increasing SO4 2– aerosol in Dhaka is yet to be investigated.

Source and respiratory deposition of trace elements in PM2.5 at an urban location in Dhaka city

“…The modes of transportation in the city include rickshaws, cycles, vans, petrol-run cars, CNG-run vehicles, motorcycles, buses, pick-up trucks, and diesel-run trucks [ 21 ]. According to the Bangladesh Road Transport Authority (BRTA), 158,417 new vehicles were registered in Dhaka in 2019 [ 22 ]. Some common industries in Bangladesh are those manufacturing bricks, sugar, pulp and paper, tanneries, pharmaceuticals, textiles, garments, chemicals, tobacco, and food and beverage [ 23 ], where petrol, diesel, octane, biomass, and natural gases are commonly used as fuel.…”

“…Dry soil, low relative humidity, little precipitation, and weak northwest wind conditions are characteristics of the winter season. During the monsoon, the chemical composition of PM 2.5 is affected by moist air and marine sea salt delivered by the air mass from the Bay of Bengal [ 22 ].…”

Wintertime Air Quality in Megacity Dhaka, Bangladesh Strongly Affected by Influx of Black Carbon Aerosols from Regional Biomass Burning

“…Fine particulate matter (PM 2.5 ) was collected with a high-volume (30 m 3 h –1 ) sampler with a PM 2.5 inlet (Digitel DH-77, Switzerland) from November 6, 2013 to February 1, 2014 including several lockdown (hartal) events. The winter sampling period (Nov 2013–Feb 2014) was chosen, as it represents the highest pollution episode of the year among four seasons in Bangladesh contribution from IGP haze on top of the local pollutions already reported by some earlier studies. , However, we collected 20 filter samples, with a 24 h collection time. During periods of strong societal lockdown/hartal, the number of motor vehicles was reduced to 10%, while most of the industries and shopping malls were shut down.…”

“…The World Health Organization (WHO) 24 h average standard for fine particulate matter (PM 2.5 ) health recommendation of 25 μg m –3 is frequently surpassed in South Asia, which hosts 14 of the world’s 15 most polluted cities . With high population density and poorly regulated emissions, Bangladesh is the country with the largest frequency of premature deaths (on average 96,000/year due to air pollution). , In addition to this grim record, the largest city, capital Dhaka, is among the most polluted cities in the world. , During the winter period, PM 2.5 concentrations may increase 4–5 times compared to the rainy season, due to the combined effects of anthropogenic activities and meteorology. − The annual average PM 2.5 concentration in Dhaka is about 90 μg m –3 with strong seasonal variations. The seasonal average PM 2.5 concentrations were 169 ± 55 (winter), 87 ± 41 (pre-monsoon), 33 ± 13 (monsoon), and 65 ± 32 μg m –3 (post-monsoon) in Dhaka. , Local sources include motor vehicles, brick kilns, metal smelters, two-stroke engines, road dust and compressed natural gas, and fugitive lead. , Long-range transported air mass also significantly contributed to the very high PM 2.5 concentrations in Dhaka especially during the winter period …”

“…The seasonal average PM 2.5 concentrations were 169 ± 55 (winter), 87 ± 41 (pre-monsoon), 33 ± 13 (monsoon), and 65 ± 32 μg m −3 (post-monsoon) in Dhaka. 8,9 Local sources include motor vehicles, brick kilns, metal smelters, two-stroke engines, road dust and compressed natural gas, and fugitive lead. 10,11 Longrange transported air mass also significantly contributed to the very high PM 2.5 concentrations in Dhaka especially during the winter period.…”