<p>A comprehensive study characterizing the extensive (scattering (<InlineEquation ID="IEq1"> <EquationSource Format="TEX">${\sigma}_{sca}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>σ</mi> <mrow> <mi mathvariant="italic">sca</mi> </mrow> </msub> </math></EquationSource> </InlineEquation>) and absorption (<InlineEquation ID="IEq2"> <EquationSource Format="TEX">${\sigma}_{abs}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>σ</mi> <mrow> <mi mathvariant="italic">abs</mi> </mrow> </msub> </math></EquationSource> </InlineEquation>) coefficients) and intensive (scattering Ångström exponent (SAE), absorption Ångström exponent (AAE), and single scattering albedo (SSA)) optical properties of near-surface aerosols, was conducted at a tropical coastal site adjoining the Eastern Arabian Sea (Goa, India) for the period from December 2019 to November 2020. Temporal (seasonal/diurnal) variations in aerosol extensive and intensive properties, and the roles of continental/marine air masses (long-range transport and land–sea-breeze circulation), boundary-layer evolution, and emission patterns in modulating the aerosol population have been examined. This is the first study at a coastal site in India to probe the SAE–AAE relationship for aerosol-type classification. Distinct seasonal variability was observed in <InlineEquation ID="IEq3"> <EquationSource Format="TEX">${\sigma}_{sca}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>σ</mi> <mrow> <mi mathvariant="italic">sca</mi> </mrow> </msub> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq4"> <EquationSource Format="TEX">${\sigma}_{abs}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>σ</mi> <mrow> <mi mathvariant="italic">abs</mi> </mrow> </msub> </math></EquationSource> </InlineEquation>, with elevated aerosol concentrations during winter and post-monsoon, attributable to the influence of continental air masses and stagnant meteorological conditions, and reduced aerosol concentrations during monsoon owing to wet scavenging and marine air intrusion. Bimodal peaks in <InlineEquation ID="IEq5"> <EquationSource Format="TEX">${\sigma}_{sca}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>σ</mi> <mrow> <mi mathvariant="italic">sca</mi> </mrow> </msub> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq6"> <EquationSource Format="TEX">${\sigma}_{abs}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>σ</mi> <mrow> <mi mathvariant="italic">abs</mi> </mrow> </msub> </math></EquationSource> </InlineEquation> during morning (08:00–09:00 h) and evening (20:00–22:00 h) indicated diurnal variations in aerosol concentrations driven by boundary-layer evolution and anthropogenic emissions, particularly during winter. Intensive optical properties revealed a seasonal transition from fine-mode, absorbing aerosols, associated with urban pollution during winter (SAE = 1.19 ± 0.15, AAE = 1.02 ± 0.18, SSA = 0.86 ± 0.04) and post-monsoon (SAE = 1.30 ± 0.19, AAE = 0.99 ± 0.19, SSA = 0.90 ± 0.04), to coarse-mode, scattering types in monsoon (SAE = 0.40 ± 0.43, AAE = 0.94 ± 0.26, SSA = 0.93 ± 0.04). The aerosol-type classification revealed low-absorbing small particles (SPLA), black carbon-dominated (BC-dominated), large particles and BC mixture (LP/BC mix), and low-absorbing large particles (LPLA) as the dominant near-surface aerosol types across seasons. Their seasonal distributions reflected a shift from continental to marine influence, with SPLA + BC-dominated aerosol types prevalent during post-monsoon (92.2%) and winter (65.6%), and LPLA + LP/BC mix (89.3%) during monsoon. The lowest mean SSA was observed for the BC-dominated aerosol type during winter (0.84), and the highest for LPLA (0.94) during monsoon. Diurnal variations were consistent across all seasons, with fine-mode (coarse-mode) aerosol types dominating during cooler nocturnal (warmer daytime) hours, indicating land–sea-breeze circulation as the primary driver. These findings underscore the complex interplay among local and upwind emission sources and atmospheric processes in shaping the aerosol regimes over tropical coastal environments.</p>

Seasonal variations in the optical properties of near-surface aerosols and the delineation of aerosol types at a tropical coastal site, Goa, adjoining the Eastern Arabian Sea

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发表日期：

2026年5月11日

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Avirup Sen,
Atiba A. Shaikh,
Harilal B. Menon

摘要

A comprehensive study characterizing the extensive (scattering ( ${\sigma}_{sca}$ $σ_{sca}$ ) and absorption ( ${\sigma}_{abs}$ $σ_{abs}$ ) coefficients) and intensive (scattering Ångström exponent (SAE), absorption Ångström exponent (AAE), and single scattering albedo (SSA)) optical properties of near-surface aerosols, was conducted at a tropical coastal site adjoining the Eastern Arabian Sea (Goa, India) for the period from December 2019 to November 2020. Temporal (seasonal/diurnal) variations in aerosol extensive and intensive properties, and the roles of continental/marine air masses (long-range transport and land–sea-breeze circulation), boundary-layer evolution, and emission patterns in modulating the aerosol population have been examined. This is the first study at a coastal site in India to probe the SAE–AAE relationship for aerosol-type classification. Distinct seasonal variability was observed in ${\sigma}_{sca}$ $σ_{sca}$ and ${\sigma}_{abs}$ $σ_{abs}$ , with elevated aerosol concentrations during winter and post-monsoon, attributable to the influence of continental air masses and stagnant meteorological conditions, and reduced aerosol concentrations during monsoon owing to wet scavenging and marine air intrusion. Bimodal peaks in ${\sigma}_{sca}$ $σ_{sca}$ and ${\sigma}_{abs}$ $σ_{abs}$ during morning (08:00–09:00 h) and evening (20:00–22:00 h) indicated diurnal variations in aerosol concentrations driven by boundary-layer evolution and anthropogenic emissions, particularly during winter. Intensive optical properties revealed a seasonal transition from fine-mode, absorbing aerosols, associated with urban pollution during winter (SAE = 1.19 ± 0.15, AAE = 1.02 ± 0.18, SSA = 0.86 ± 0.04) and post-monsoon (SAE = 1.30 ± 0.19, AAE = 0.99 ± 0.19, SSA = 0.90 ± 0.04), to coarse-mode, scattering types in monsoon (SAE = 0.40 ± 0.43, AAE = 0.94 ± 0.26, SSA = 0.93 ± 0.04). The aerosol-type classification revealed low-absorbing small particles (SPLA), black carbon-dominated (BC-dominated), large particles and BC mixture (LP/BC mix), and low-absorbing large particles (LPLA) as the dominant near-surface aerosol types across seasons. Their seasonal distributions reflected a shift from continental to marine influence, with SPLA + BC-dominated aerosol types prevalent during post-monsoon (92.2%) and winter (65.6%), and LPLA + LP/BC mix (89.3%) during monsoon. The lowest mean SSA was observed for the BC-dominated aerosol type during winter (0.84), and the highest for LPLA (0.94) during monsoon. Diurnal variations were consistent across all seasons, with fine-mode (coarse-mode) aerosol types dominating during cooler nocturnal (warmer daytime) hours, indicating land–sea-breeze circulation as the primary driver. These findings underscore the complex interplay among local and upwind emission sources and atmospheric processes in shaping the aerosol regimes over tropical coastal environments.