Evaluation of optical particulate matter sensors under realistic conditions of strong and mild urban pollution

In this paper we evaluate characteristics of three optical particulate matter sensors/sizers (OPS): high-end spectrometer 11-D (Grimm, Germany), low-cost sensor OPC-N2 (Alphasense, United Kingdom) and in-house developed MAQS which is based on another low-cost sensor - PMS5003 (Plantower, China), under realistic conditions of strong and mild urban pollution. Results were compared against a reference gravimetric system, based on Gemini (Dadolab, Italy), 2.3 m3/h air sampler, with two channels (simultaneously measuring PM2.5 and PM10 concentrations). The measurements were performed in Sarajevo, the capital of Bosnia-Herzegovina, from December 2019 until May 2020. This interval is divided into period 1 - strong pollution (December 2019 - March 2020) and period 2 - mild pollution (March 2020 - May 2020). The city of Sarajevo is one of the most polluted cities in Europe in terms of aerosols: the average concentration of PM2.5 during the period 1 was 83 ug/m3, with daily aveverage values exceeding 500 ug/m3. During period 2, the average concentration of PM2.5 was 20 ug/m3. These conditions represent a good opportunity to
test optical devices against reference instrument in a wide range of ambient particulate matter (PM) concentrations. The effect of an in-house developed diffusion dryer for 11-D is discussed as well. In order to analyze the mass distribution of aerosols, a scanning mobility particle sizer (SMPS) spectrometer, which together with the 11-D spectrometer gives the full spectrum from nanoparticles of diameter 10 nm to coarse particles of diameter 35 um, was used. All tested devices showed excellent correlation with the reference instrument in period 1, with R^2 values between 0.90 and 0.99 for daily average PM concentrations. However, in period 2, where the range of concentrations was much narrower, R^2 values decreased significantly, to values from 0.28 to 0.92. We have also included results of a 13.5 month long-term comparison of our MAQS sensor with a nearby beta attenuation monitor (BAM) 1020 (Met One Instruments, USA) operated by the United States Environmental Protection Agency (US EPA), which showed similar correlation and no observable change of performance over time.

This dataset contains:
1. preliminary.csv - hourly average PM2.5 and PM10 values for 8 MAQS sensors during the preliminary test period
2. meteo.csv - ambient air temperature and relative humidity, hourly average values
3. PM_reference_timeseries.csv - timeseries of data from reference air sampler, including PM2.5, PM10, average air temperature, average air pressure, actual air volume and mass difference (loaded-blank) of each filter
4. main.csv - comparisons of 11-D, OPC-N2 and MAQS sensor against the reference during the campaign
5. dryer_effect.csv - hourly average data of ambient air vs 11-D internal, temperature and relative humidity. Dryer was installed on 03/12/2020 15:30
6. SMPS.zip (4 files) - wide-range spectrometer (SMPS with 11-D) csv files for density plots: time, Log(Dp) and concentration values (both absolute and normalized), based on hourly average data
7. histograms.zip (8 files) - selected wide-range histograms, based on hourly average data from SMPS and 11-D
8. BAM.zip (5 files) - long-term comparisons of MAQS sensor with a nearby BAM. Hourly (BAM1.csv), daily (BAM2.csv) and monthly (BAM3.csv) average values and comaparison of two MAQS sensors 300 meters apart, hourly (BAM4.csv) and daily (BAM5.csv) values