ATMOSPHERIC PARTICULATE MATTER WITH DIAMETERS SMALLER THAN 2.5 UM (PM2.5) IS A POLLUTANT THAT CONTRIBUTES TO THE DEVELOPMENT OF HUMAN DISEASE. SATELLITE-DERIVED ESTIMATES OF SURFACE-LEVEL PM2.5 CONCENTRATIONS CAN CONTRIBUTE GREATLY TO OUR UNDERSTANDING OF HOW PARTICULATE MATTER AFFECTS HEALTH. HOWEVER THESE SATELLITE-DERIVED PM2.5 ESTIMATES ARE OFTEN UNCERTAIN DUE TO A LACK OF INFORMATION ABOUT THE RATIO OF AEROSOL OPTICAL DEPTH (AOD) WHICH THE PRIMARY AEROSOL RETRIEVAL MADE BY SATELLITE INSTRUMENTS AND SURFACE-LEVEL PM2.5. SURFACE MONITORING NETWORKS FOR CO-INCIDENT PM2.5 AND AOD MEASUREMENTS ARE EXTREMELY RARE EVEN IN THE NORTH AMERICA. THIS PROPOSAL AIMS TO ADDRESS THE PM2.5:AOD CHARACTERIZATION PROBLEM BY DEPLOYING A CITIZEN-BASED MONITORING NETWORK FOR PM2.5 AND AOD AT SPATIAL AND TEMPORAL SCALES NEVER-BEFORE ACHIEVED AND IN REGIONS WITH LARGE EXPECTED GRADIENTS IN PM2.5 (CITIZEN-ENABLED AEROSOL MEASUREMENTS FOR SATELLITES [CEAMS]). CEAMS WILL LEVERAGE NOVEL LOW-COST MEASUREMENT TECHNOLOGY THAT CAN BE DEPLOYED AT SCALES OF 100S TO POTENTIALLY 1000S OF UNITS. WE WILL LEVERAGE SUPPORT FROM EXISTING SUCCESSFUL CITIZEN-SCIENCE NETWORKS TO DEVELOP BEST-PRACTICES THAT ENSURE SUSTAINABILITY AND SUCCESS OF CEAMS. THE PROJECT HAS THREE PRIMARY AIMS: AIM 1 (PROTOTYPE PHASE): CONDUCT A PILOT STUDY OF A LOW-COST SENSOR FOR PM2.5 AND AOD IN A PANEL OF COLORADO CITIZEN-SCIENTISTS. VALIDATE THESE DATA AGAINST STANDARD PM2.5 AND AOD MEASUREMENTS. ALL PROTOTYPE PHASE OBJECTIVES WERE COMPLETED SUCCESSFULLY. TWENTY-THREE CEAMS SAMPLERS WERE CONSTRUCTED AND VALIDATED AGAINST STANDARD REFERENCE INSTRUMENTS. THE FILTER-BASED PM2.5 MEASUREMENT GAVE STRONG CORRELATION WITH AN EPA FEDERAL REFERENCE MONITOR (R = 0.93) AND AN AVERAGE ERROR OF LESS THAN 10%. VALIDATION OF THE AOD MEASUREMENT AGAINST IN-USE AERONET MONITORS GAVE A MEAN ABSOLUTE ERROR OF LESS THAN 0.01 AOD UNITS AND AN AVERAGE BIAS OF 3%. A PROJECT WEBSITE SOCIAL MEDIA ACCOUNTS AND TRAINING MATERIALS WERE DEVELOPED. A PANEL OF 30 CITIZEN SCIENTISTS WERE RECRUITED TO PARTICIPATE IN THE CEAMS PILOT. FOLLOWING TRAINING MORE THAN 150 SUCCESSFUL AOD MEASUREMENTS AND 50 PM2.5 MEASUREMENTS WERE COLLECTED BY THE CITIZEN SCIENTISTS WITH RELATIVELY HIGH COMPLIANCE AND GOOD AGREEMENT BETWEEN MEASUREMENTS. DATA FROM CEAMS DEMONSTRATED SUBSTANTIAL VARIABILITY IN MEASURED PM2.5:AOD RATIOS WITHIN A SINGLE 10X10 KM GRID PIXEL (MORE THAN CAN BE EXPLAINED BY MEASUREMENT ERROR ALONE); THESE RESULTS DEMONSTRATE THE NEED FOR MORE SPATIALLY AND TEMPORALLY RESOLVED MEASUREMENTS OF THIS RATIO TO IMPROVE SATELLITE-DERIVED ESTIMATES. HANDS-ON TRAININGS (VS. WEB-BASED TRAINING) SUBSTANTIALLY IMPROVED PARTICIPANT PERFORMANCE RELATED TO INSTRUMENT SET-UP CALIBRATION MEASUREMENT AND DATA TRANSFER. AIM 2 (IMPLEMENTATION PHASE): EXPAND THE CEAMS NETWORK TO HUNDREDS OF STATIONS ACROSS TWO URBAN AREAS AND ONE RURAL SMOKE-PRONE AREA. AIM 3 (IMPLEMENTATION PHASE): USE THE DATA FROM CEAMS TO CONSTRAIN SPATIAL AND TEMPORAL VARIABILITY IN SURFACE PM2.5 AND TO VALIDATE SATELLITE-DERIVED PM2.5 ESTIMATES AT HIGH-RESOLUTION. DEVELOP PARAMETERIZATIONS OF SPATIAL/TEMPORAL PM2.5:AOD VARIABILITY BASED ON HIGH-RESOLUTION EMISSIONS FIELDS METEOROLOGY AND LAND SURFACE FEATURES.