Offline aerosol mass spectrometer (AMS) measurements can provide valuable information about ambient organic aerosols in areas and periods in which online AMS measurements are not available. However, these offline measurements have a low temporal resolution, as they are based on filter samples usually collected over 24 h. In this study, we examine whether and how this low time resolution affects source apportionment results. We used a five-month period (November 2016–March 2017) of online measurements in Athens, Greece, and performed positive matrix factorization (PMF) analysis to both the original dataset, which consists of 30 min measurements, and to time averages from 1 up to 24 h. The 30 min results indicated that five factors were able to represent the ambient organic aerosol (OA): a biomass burning organic aerosol factor (BBOA), which contributed 16 % of the total OA; hydrocarbon-like OA (HOA) (29 %); cooking OA (COA) (20 %); more-oxygenated OA (MO-OOA) (18 %); and less-oxygenated OA (LO-OOA) (17 %). Use of the daily averages resulted in estimated average contributions that were within 8 % of the total OA compared with the high-resolution analysis for the five-month period. The most important difference was for the BBOA contribution, which was overestimated (25 % for low resolution versus 17 % for high resolution) when daily averages were used. The estimated secondary OA varied from 35 % to 28 % when the averaging interval varied between 30 min and 24 h. The high-resolution results are expected to be more accurate, both because they are based on much larger datasets and because they are based on additional information about the temporal source variability. The error for the low-resolution analysis was much higher for individual days, and its results for high-concentration days in particular are quite uncertain. The low-resolution analysis introduces errors in the determined AMS profiles for the BBOA and LO-OOA factors but determines the rest relatively accurately (theta angle around 10^∘ or less).

中文翻译：

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离线应用期间气溶胶质谱仪测量的 PMF 分析平均周期的影响

离线气溶胶质谱仪 (AMS) 测量可以提供有关无法进行在线 AMS 测量的区域和时期的环境有机气溶胶的有价值信息。然而，这些离线测量具有较低的时间分辨率，因为它们基于通常在 24 小时内收集的过滤器样本。在这项研究中，我们研究了这种低时间分辨率是否以及如何影响源分配结果。我们在希腊雅典使用了为期五个月（2016 年 11 月至 2017 年 3 月）的在线测量，并对包含 30 分钟测量的原始数据集和从 1长达 24 小时。30 分钟的结果表明，五个因子能够代表环境有机气溶胶 (OA)：生物质燃烧有机气溶胶因子 (BBOA)，占总 OA 的 16%；类烃 OA (HOA) (29 %)；烹饪 OA (COA) (20 %); 含氧量更高的 OA (MO-OOA) (18 %)；和低氧 OA (LO-OOA) (17 %)。与五个月期间的高分辨率分析相比，使用每日平均值导致估计的平均贡献在总 OA 的 8% 以内。最重要的区别在于 BBOA 的贡献，当使用每日平均值时，它被高估了（低分辨率为 25%，高分辨率为 17%）。当平均间隔在 30 分钟到 24 小时之间变化时，估计的继发性 OA 从 35% 到 28% 不等。高分辨率结果预计会更准确，因为它们基于更大的数据集，并且因为它们基于有关时间源可变性的附加信息。个别天的低分辨率分析误差要大得多，尤其是高浓度天的结果非常不确定。低分辨率分析在确定的 AMS 剖面中引入了 BBOA 和 LO-OOA 因子的误差，但相对准确地确定了其余部分（θ 角约为 10^∘或更少）。