Anna Ripoll

Intercomparisons of Mobility Size Spectrometers and Condensation Particle Counters in the Frame of the Spanish Atmospheric Observational Aerosol Network

Red Española de DMAs Ambientales (REDMAAS), the Spanish network of environmental differential mobility analyzers (DMAs), currently comprises six research groups involved in the measurement of atmospheric aerosol size distributions by means of DMAs. The aim of this network is to guarantee the good quality and comparability of the routine measurements carried out at each location and in diverse environments across Spain. In order to achieve this objective, one of its main activities is the annual intercomparison of mobility size spectrometers used within the network (five units of scanning mobility particle sizers [SMPS] and one ultrafine particle monitor [UFPM]). Here we report the 2main results obtained during the 2010–2012 campaigns, including a study on particle deposition in dryers used in ambient air sampling systems. In general, all instruments showed good performance with deviations in accepted tolerance. The intercomparisons have been proved to be a useful exercise to detect instrument problems, such as incorrect calibrations. DMA calibration checks were performed with polystyrene latex reference particles. Deviations of less than 1% were observed during the first year, which increased 4.7% during the last campaign. Some differences among the responses of different condensation particle counter (CPC) models were encountered, being mainly connected to the intrinsic characteristics of each counter. The comparison of UFPM with CPCs has given good results. The SMPS intercomparisons, especially for particles above 20 nm, have been within +/−15% tolerance. Regarding particle deposition in dryers used in sampling systems, particle penetration was lower than predicted by the recommended model. This result was probably due to the fact that not all the possible mechanisms were considered in the model. Copyright 2015 American Association for Aerosol Research

Testing the performance of sensors for ozone pollution monitoring in a citizen science approach

Tropospheric ozone (O3) is an environmental pollutant of growing concern, especially in suburban and rural areas where the density of air quality monitoring stations is not high. In this type of areas citizen science strategies can be useful tools for awareness raising, but sensor technologies must be validated before sensor data are communicated to the public. In this work, the performance under field conditions of two custom-made types of ozone sensing devices, based on metal-oxide and electrochemical sensors, was tested. A large array of 132 metal-oxide (Sensortech MICS 2614) and 11 electrochemical (Alphasense) ozone sensors, built into 44 sensing devices, was co-located at reference stations in Italy (4 stations) and Spain (5). Mean R2 between sensor and reference data was 0.88 (0.78-0.96) and 0.89 (0.73-0.96) for Captor (metal-oxide) and Raptor (electrochemical) nodes. The metal-oxide sensors showed an upper limit (approximately 170 μg/m3) implying that these sensors may be useful to communicate mean ozone concentrations but not peak episodes. The uncertainty of the nodes was 10% between 100 and 150 μg/m3 and 20% between 150 and 200 μg/m3, for Captors, and 10% for >100 μg/m3 for Raptors. Operating both types of nodes up to 5 months did not evidence any clear influence of drifts. The use of these sensors in citizen science can be a useful tool for awareness raising. However, significant data processing efforts are required to ensure high data quality, and thus machine learning strategies are advisable. Relative uncertainties should always be reported when communicating ozone concentration data from sensing nodes.