Biomass burning (BB) is a major source of atmospheric particulate matter (PM), influencing air quality, public health, and climate from local to global scales. Its importance is expected to grow under a changing climate, driven by changes in wildfire frequency and intensity, agricultural burning practices, and residential fuel use. This work explores the contribution and characteristics of biomass burning aerosols across a range of urban environments, drawing on observations from both developing and developed cities, including Delhi (India), Chiang Mai (Thailand), Beijing (China), Dammam (Saudi Arabia), Paris and Grenoble (France), California (USA), and Birmingham (UK). A range of source apportionment approaches, including Positive Matrix Factorisation (PMF), Aethalometer model, molecular tracer measurements, and radiocarbon (14C) analysis, were used to identify biomass burning sources and quantify their contributions to PM. The results show that biomass burning is a widespread source of urban particulate pollution, although its contribution and characteristics vary considerably between regions. Biomass burning contributed between approximately 5% and 60% of PM2.5, with substantially higher impacts during severe haze events and periods of intense agricultural burning. Organic molecular tracers, including levoglucosan, mannosan, galactosan, and resin acids, proved valuable for distinguishing fuel types and combustion sources. Comparisons between developing and developed cities reveal both common aerosol signatures and region-specific characteristics, highlighting the need for targeted mitigation strategies. These findings provide new insights into the role of biomass burning aerosols in urban environments and their implications for future air quality and climate management.