Haze-fog conditions over northern India are associated with visibility degradation and severe attenuation of solar radiation by airborne particles with various chemical compositions. PM2.5 samples have been collected in Delhi, India from December 2011 to November 2012 and analyzed for carbonaceous and inorganic species. PM10 measurements were made simultaneously such that PM10–2.5 could be estimated by difference. This study analyzes the temporal variation of PM2.5 and carbonaceous particles (CP), focusing on identification of the primary and secondary aerosol emissions, estimations of light extinction coefficient (bext) and the contributions by the major PM2.5 chemical components. The annual mean concentrations of PM2.5, organic carbon (OC), elemental carbon (EC) and PM10–2.5 were found to be 153.6 ± 59.8, 33.5 ± 15.9, 6.9 ± 3.9 and 91.1 ± 99.9 μg m−3, respectively. Total CP, secondary organic aerosols and major anions (e.g., SO42− and NO3−) maximize during the post-monsoon and winter due to fossil fuel combustion and biomass burning. PM10–2.5 is more abundant during the pre-monsoon and post-monsoon. The OC/EC varies from 2.45 to 9.26 (mean of 5.18 ± 1.47), indicating the influence of multiple combustion sources. The bext exhibits highest values (910 ± 280 and 1221 ± 371 Mm−1) in post-monsoon and winter and lowest in monsoon (363 ± 110 and 457 ± 133 Mm−1) as estimated via the original and revised IMPROVE algorithms, respectively. Organic matter (OM =1.6 × OC) accounts for ~39 % and ~48 % of the bext, followed by (NH4)2SO4 (~21 % and ~24 %) and EC (~13 % and ~10 %), according to the original and revised algorithms, respectively. The bext estimates via the two IMPROVE versions are highly correlated (R2 = 0.95, root mean square error = 38 % and mean bias error = 28 %) and are strongly related to visibility impairment (r = −0.72), mostly associated with anthropogenic rather than natural PM contributions. Therefore, reduction of CP and precursor gas emissions represents an urgent opportunity for air quality improvement across Delhi.

中文翻译：

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德里 PM2.5 化学成分评估：一次排放与二次排放以及对消光系数和能见度降低的贡献

印度北部的雾霾状况与能见度降低和具有各种化学成分的空气中颗粒对太阳辐射的严重衰减有关。2011 年 12 月至 2012 年 11 月在印度德里收集了 PM2.5 样本，并分析了碳质和无机物种。PM10 测量是同时进行的，这样 PM10-2.5 就可以通过差异来估计。本研究分析了 PM2.5 和碳质颗粒 (CP) 的时间变化，重点是识别初级和次级气溶胶排放、估计消光系数 (bext) 以及 PM2.5 主要化学成分的贡献。PM2.5、有机碳（OC）、元素碳（EC）和PM10-2.5的年平均浓度分别为153.6±59.8、33.5±15.9、6.9±3.9和91.1±99。分别为 9 μg m-3。由于化石燃料燃烧和生物质燃烧，总 CP、二次有机气溶胶和主要阴离子（例如 SO42- 和 NO3-）在季风后和冬季达到最大。PM10-2.5 在季风前和季风后更丰富。OC/EC 在 2.45 到 9.26 之间变化（平均值为 5.18 ± 1.47），表明多个燃烧源的影响。bext 在季风后和冬季表现出最高值（910 ± 280 和 1221 ± 371 Mm-1），在季风中最低（363 ± 110 和 457 ± 133 Mm-1），分别通过原始和修订的 IMPROVE 算法估计. 有机物 (OM = 1.6 × OC) 占 Bext 的 ~39% 和 ~48%，其次是 (NH4)2SO4（~21% 和 ~24%）和 EC（~13% 和 ~10%），根据分别为原始算法和修改后的算法。通过两个 IMPROVE 版本的 Bext 估计高度相关（R2 = 0.95，均方根误差 = 38 % 和平均偏差误差 = 28 %）并且与能见度损害密切相关（r = -0.72），主要与人为而非比自然 PM 贡献。因此，减少 CP 和前体气体排放是德里改善空气质量的紧迫机会。