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Technical note: An improved approach to determining background aerosol concentrations with PILS sampling on aircraft

机译：技术说明：一种改进的方法，可通过飞机上的PILS采样确定背景气溶胶浓度

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Particle-into-Liquid Samplers (PILS) have become a standard aerosol collection technique, and are widely used in both ground and aircraft measurements in conjunction with off-line ion chromatography (IC) measurements. Accurate and precise background samples are essential to account for gas-phase components not efficiently removed and any interference in the instrument lines, collection vials or off-line analysis procedures. For aircraft sampling with PILS, backgrounds are typically taken with in-line filters to remove particles prior to sample collection once or twice per flight with more numerous backgrounds taken on the ground. Here, we use data collected during the Front Range Air Pollution and Photochemistry Experiment (FRAPPE) to demonstrate that not only are multiple background filter samples are essential to attain a representative background, but that the chemical background signals do not follow the Gaussian statistics typically assumed. Instead, the background signals for all chemical components analyzed from 137 background samples (taken from similar to 78 total sampling hours over 18 flights) follow a log-normal distribution, meaning that the typical approaches of averaging background samples and/or assuming a Gaussian distribution cause an over-estimation of background samples and thus an underestimation of sample concentrations. Our approach of deriving backgrounds from the peak of the log-normal distribution results in detection limits of 0.25, 032, 3.9, 0.17, 0.75 and 0.57 mu g m(-3) for sub-micron aerosol nitrate (NO3-), nitrite (NO2-), ammonium (NH4+), sulfate (SO42-), potassium (K+) and calcium (Ca2+), respectively. The difference in backgrounds calculated from assuming a Gaussian distribution versus a log-normal distribution were most extreme for NH4+, resulting in a background that was 1.58x that determined from fitting a log-normal distribution. (C) 2016 Elsevier Ltd. All rights reserved.
机译：颗粒状液体采样器（PILS）已成为一种标准的气溶胶收集技术，并与离线离子色谱（IC）测量结合广泛用于地面和飞机测量中。准确而精确的背景样品对于解决气相成分未被有效去除以及对仪器管线，收集瓶或离线分析程序的任何干扰至关重要。对于使用PILS进行飞机采样，通常在每次飞行采样一次或两次之前，使用在线过滤器采集背景以去除颗粒，而地面上会采集更多的背景。在这里，我们使用在“远距离空气污染和光化学实验”（FRAPPE）期间收集的数据来证明，不仅多个背景过滤器样本对于获得代表性背景至关重要，而且化学背景信号未遵循通常假定的高斯统计。取而代之的是，从137个背景样品中分析的所有化学成分的背景信号（取自18个航班的约78个总采样小时）遵循对数正态分布，这意味着对背景样品取平均值和/或采用高斯分布的典型方法会导致背景样品的高估，从而导致样品浓度的低估。我们从对数正态分布的峰值得出背景的方法导致亚微米气溶胶硝酸盐（NO3-），亚硝酸盐（NO2）的检出限分别为0.25、032、3.9、0.17、0.75和0.57μgm（-3） -），铵（NH4 +），硫酸盐（SO42-），钾（K +）和钙（Ca2 +）。对于NH4 +，假设高斯分布与对数正态分布的背景差异最大，导致背景的1.58倍是通过拟合对数正态分布确定的。 （C）2016 Elsevier Ltd.保留所有权利。

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