In this study, we investigated the intra-urban variability of fine particle mass (PM) and ultrafine particle number concentration (PNC) in Dhaka (Bangladesh), and Pittsburgh (USA), two cities with vastly different pollution sources and levels. We collected measurements of PNC and PM at a wide range of sites spanning a variety of urban land use attributes (35 sites in Dhaka and 30 sites in Pittsburgh). We found that PNC levels exhibited a 3-4-fold variability between sites in each city, ranging from 20,000–100,000 # cm in Dhaka and 7,000–28,000 # cm in Pittsburgh. PM levels varied within 50% of the urban background level, ranging from 80 to 110 μg m in Dhaka and 6–12 μg m in Pittsburgh. We observed a moderate level of spatial correlation between PNC and PM measurements in both cities (R 0.3 in Dhaka, and 0.4 in Pittsburgh), and consistent within-city spatial patterns in different meteorological seasons. Compared to the Pittsburgh levels, both PNC and PM levels in Dhaka were significantly higher, however, PM was disproportionately higher (10–12 times higher) than PNC (3–4 times higher). The slope of PNC versus PM varied significantly between the two cities, suggesting that the sources and size distribution of particles that make up the majority of the PM were different in the two cities. The results found in Dhaka indicate that aerosol particles are influenced by solid fuel combustion, including solid biomass burning, waste burning, and road dust, which have a greater impact on particle mass concentration due to their larger size. Contrary, in Pittsburgh, traffic (gasoline and diesel combustion) particles, relatively smaller in size compared to solid fuel combustion particles, play a dominant role in determining the within-city variability of PNC and PM. Our findings suggest that while controlling traffic emissions can contribute to reducing PNC, substantial efforts will be required to mitigate accumulation mode particles from various region-specific sources in order to decrease PM mass concentrations in Dhaka.

中文翻译：

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孟加拉国达卡和美国匹兹堡的城市内超细颗粒数量和细颗粒质量浓度变化对比

在这项研究中，我们调查了达卡（孟加拉国）和匹兹堡（美国）这两个污染源和水平截然不同的城市的细颗粒物质量 (PM) 和超细颗粒物数量浓度 (PNC) 的城市内变异性。我们收集了涵盖各种城市土地利用属性的多个地点（达卡的 35 个地点和匹兹堡的 30 个地点）的 PNC 和 PM 测量值。我们发现每个城市的地点之间的 PNC 水平存在 3-4 倍的变异性，达卡的范围为 20,000-100,000 # cm，匹兹堡的范围为 7,000-28,000 # cm。 PM 水平在城市背景水平的 50% 范围内变化，达卡为 80 至 110 微克/立方米，匹兹堡为 6-12 微克/立方米。我们观察到两个城市的 PNC 和 PM 测量之间存在中等水平的空间相关性（达卡的 R 为 0.3，匹兹堡的 R 为 0.4），并且不同气象季节的城市内空间模式一致。与匹兹堡的水平相比，达卡的 PNC 和 PM 水平均显着较高，但 PM 的水平不成比例地高于 PNC（高出 3-4 倍）（高出 10-12 倍）。两个城市之间 PNC 与 PM 的斜率差异很大，这表明两个城市中构成 PM 大部分的颗粒物的来源和粒径分布不同。达卡的结果表明，气溶胶颗粒受到固体燃料燃烧的影响，包括固体生物质燃烧、废物燃烧和道路灰尘，由于其尺寸较大，对颗粒质量浓度的影响更大。相反，在匹兹堡，与固体燃料燃烧颗粒相比，交通（汽油和柴油燃烧）颗粒的尺寸相对较小，在确定 PNC 和 PM 的城市内变异性方面发挥着主导作用。我们的研究结果表明，虽然控制交通排放有助于减少 PNC，但仍需要做出大量努力来减少来自不同地区特定来源的累积模式颗粒物，以降低达卡的 PM 质量浓度。