Observation and Data Analysis of Fine Particle Concentrations on the Territory of Bulgaria for the Period of 2018-2025

A dataset comprising raw particulate matter (PM) measurements from the METER.AC monitoring network (https://meter.ac), along with comprehensive analysis results covering the territory of Bulgaria for the period 2018–2025, based on data from over 200 monitoring sites. The METER.AC network is a national-scale air quality monitoring system across the territory of Bulgaria, comprising more than 200 sensor nodes strategically distributed to capture spatial and temporal variations in air quality. Each node is equipped with low-cost yet reliable optical particle sensors, as well as temperature and humidity sensors, and microcontrollers for local data acquisition and processing. Data processing pipeline was implemented using a Python-based Ploomber workflow. The source code for the analytical pipeline, along with the corresponding *.yaml configuration files, is available at: https://github.com/PUCompChem/timeseriesutils/tree/main/analysis_workflow File description: meter_ac_raw_data_parsed.zip archive contains the raw data from all METER.AC nodes for the period 2018-2025. It includes individual CSV files for each monitoring location. The data were extracted from the METER.AC platform and converted into the input format required by the Ploomber workflow. The remaining files contain outputs generated by the various Ploomber workflow tasks. The file correlation_profiles_by_we.csv and correlation_profiles_locations_population_by_day.csv contain correlaton profiles for each location, defined by the coefficients of a quadratic regression model of the form PM = a.T^2 + b.T + c, together with the associated coefficient of determination (R^2). The x_histograms_2019-2024_we.zip archive contains histograms of the coefficient b (primary regression slope) values across multiple years. Compliance with European air quality standards under Directive 2008/50/EC was assessed by comparing measured concentrations against maximum permissible values (MPVs) for both annual and daily exposure. The regulation_pm_results.zip archive contains a set of HTML files with visualizations representing MPVs derived from annual mean concentrations over a seven-year period for each monitoring location. Light green and light blue bubbles indicate exceedances of the regulatory limits for PM10 and PM2.5, respectively, as denoted by the threshold lines. Addirionally, MPVs based on daily averaged concentrations are presented on a monthly basis, where red markers indicate days on which PM10 levels exceeded the permissible limits. Several complementary outlier analyses are provided. The PCA_2023.zip archive contains the principal component analysis (PCA) results, while Outlier_detection_2023.zip includes outputs from the z-score–based outlier detection method. The Clustering_2023.zip archive presents dendrograms illustrating clustering results obtained under different methodological settings. Additionally, several sample (demo) PNG files are included to provide a quick preview of the archive contents.