• Measurement and surveillance patterns show methodological consolidation across air quality research, emphasizing standardized sampling, surveillance networks, indoor-outdoor exposure protocols, and high-resolution instrumental analysis (adsorption columns, mass spectrometry) [4], [10], [11], [16].

• Particulate matter structure and urban PM characterization converge on size-resolved sampling, mass concentration, and gas-particle partitioning, linking particulate distributions to chemical composition in Boston and other urban environments [5], [6], [7], [8], [14].

• Sulfur chemistry and photochemical oxidation dominate early air pollution theory, with SO2 oxidation, urban sulfate variability, sulfur emissions, and bioindicator approaches shaping risk assessment [1], [2], [3], [14], [19].

• Source attribution and urban dynamics are advanced via multivariate analyses, elemental balances, and city-scale source discrimination to map pollution origins and pathways [13], [17], [18], [20].

• Organic aerosols and hydrocarbons reveal gas-particle partitioning and organic geochemistry in urban atmospheres, integrating hydrocarbon profiles with inorganic PM to explain composition and formation [7], [8], [9].