Bias caused by water adsorption in hourly PM measurements

Abstract

Abstract. Beta-attenuation monitors are used worldwide to monitor PM mass concentration with high temporal resolution. Hourly PM10 and PM2. 5 dry mass concentrations are publicly available with the tacit assumption that water is effectively removed prior to the measurement. However, as both the filter material of the monitor and the aerosol particles are capable of retaining a significant amount of water even at low relative humidities, the basic assumption may not be valid, resulting in significant bias in reported PM10 and PM2. 5 concentrations. Here we show that in PM10 measurement, particle-free air can produce apparent hourly average PM concentrations in the range of −13–+21 µg m−3 under conditions of fluctuating relative humidity. Positive and negative apparent readings are observed with increasing and decreasing relative humidities, respectively. Similar phenomena have been observed when the instrument filter was previously loaded with atmospheric aerosol. As a result the potential measurement biases in hourly readings arising from the interaction with water may be in the range of −53… + 69 %.

Characterizing the regional contribution to PM10 pollution over northern France using two complementary approaches: Chemistry transport and trajectory-based receptor models

“…The obtained maps showed non-significant differences with correlation coefficients of around 0.9 and average absolute relative deviations of about 2 % for both the CF and PSCF. These results compare well with the position error of 20 % found by (Kiss et al, 2017) for trajectories computed from analyzed wind fields. Lastly, the influence of the spatial resolution of the gridded domain was also tested within the Zefir package considering grid cells of 1.0 o x 1.0 o , 0.5 o x 0.5 o or 0.1 o x 0.1 o in size and was considered low with a maximum average absolute relative deviations of 24 % since non-significant differences in geographical source area maps were observed.…”

“…In this study, a qualitative uncertainty assessment was performed for the output CF/PSCF maps taking into account the precision of the input data. The uncertainty of the measured tri-hourly concentrations of PM 10 was estimated to be less than 50 % (Kiss et al, 2017). However, because the deterministic CTM approach considers measured PM 10 concentrations as "true" values, here the uncertainty of the measured values will not be considered.…”

A bulk-mass-modeling-based method for retrieving particulate matter pollution using CALIOP observations

“…Using parameters provided in the L2_05kmAPro product, as well as the corresponding Level 2 5 km aerosol layer (L2_05kmALay) product, a robust quality-assurance (QA) procedure for the aerosol observations was implemented (Table 1). Further information on the QA metrics and screening protocol are discussed in detail in previous studies (Kittaka et al, 2011;Campbell et al, 2012;Toth et al, 2013Toth et al, , 2016. Once the QA procedure was applied, the aerosol profiles were linearly re-gridded from 60 m vertical resolution (above mean sea level, a.m.s.l.)…”

The Effects of PM2.5 Concentrations and Relative Humidity on Atmospheric Visibility in Beijing

“…However, as both the filter material of the monitor and the aerosol particles are capable of retaining a significant amount of water even at low RH, the basic assumption may not be valid, resulting in significant bias in reported PM 2.5 concentrations (Chow, 1995;Perrino et al, 2013). Adsorbed water may be partly retained on the filter and particulates even at low RHs (called hysteresis; Kiss et al, 2017). The magnitude of water retention strongly depends on the filter material.…”