OUR OVERARCHING GOAL IS TO INCREASE THE VALUE OF NASA EARTH SCIENCE PRODUCTS FOR MONITORING FINE PARTICULATE MATTER (PM2.5) NEAR THE EARTH S SURFACE. SATELLITE AEROSOL OPTICAL DEPTH (AOD) IS A MEASURE OF THE INTEGRATED AEROSOL LOADING THROUGH THE ENTIRE COLUMN OF THE ATMOSPHERE. SURFACE PM2.5 CAN BE PREDICTED FROM SATELLITE AOD BY INCORPORATING DATA FROM FIXED GROUND MONITORS AND ADDITIONAL A PRIORI ASSUMPTIONS. HOWEVER SATELLITE-DERIVED SURFACE PM2.5 REMAINS HIGHLY UNCERTAIN DUE TO LIMITED HIGH-QUALITY POINT MEASUREMENTS AND UNCERTAINTIES IN AOD-PM2.5 RELATIONSHIPS FOR DIFFERENT REGIONS. TO ADDRESS THESE CHALLENGES WE PROPOSE TO COLLECT SPATIALLY DENSE QUALITY PM2.5 DATA USING LOW-COST SENSORS DEPLOYED BY CITIZEN SCIENTISTS IN THREE REGIONS REPRESENTING LOW (RALEIGH NC) MODERATE (LOS ANGELES CA) AND HIGH (DELHI INDIA) PM2.5 LOADINGS. THE SURFACE PM2.5 GRADIENTS FROM SENSORS CAN BE USED TO VALIDATE GRADIENTS IN SATELLITE-DERIVED PM2.5 AND HELP FINE-TUNE REGION-SPECIFIC INTERPRETATION OF SATELLITE DATA FOR PM2.5 MONITORING. BY LEVERAGING LOCAL CITIZEN SCIENTISTS AND OPEN DATA PLATFORM SUCH EFFORTS CAN BE COST-EFFECTIVE AND SUSTAINABLE WHILE ALSO ENHANCING NASAS MISSION. DURING THE PROTOTYPE PHASE (PHASE 1) WE EVALUATED 20 COMMERCIAL LOW-COST SENSORS IN THE LAB AND FIELD UNDER VARYING CONDITIONS. OF THESE THE PURPLEAIR PA-II SENSOR MET OUR 10-POINT CRITERIA FOR FIELD DEPLOYMENT BY CITIZEN SCIENTISTS IN THE LOS ANGELES BASIN. THE DATA SHOW EXCELLENT PERFORMANCE BY PA-II SENSORS BUT HIGHLIGHT THE NEED FOR IN-FIELD CALIBRATION IN THE REGION OF INTEREST. TO DATE 48 CITIZEN SCIENTISTS (AGED 15 TO 55+) HAVE BEEN RECRUITED FOR SENSOR DEPLOYMENT THROUGH OUTREACH WITH SCHOOLS AND UNIVERSITIES AND WORD-OF-MOUTH. CITIZEN SCIENTISTS WERE ENGAGED IN A 1-DAY WORKSHOP THAT INCLUDED HANDS-ON ACTIVITIES FOLLOWED BY CONTINUAL ENGAGEMENT VIA ONLINE BLOGS SCHOOL PROJECTS ETC. A WEBSITE WITH A PRELIMINARY DATA DISPLAY SYSTEM HAS BEEN DEVELOPED (AQCITIZENSCIENCE.RTI.ORG). IN THE IMPLEMENTATION PHASE (PHASE 2) WE WILL BUILD ON THE KEY LESSONS LEARNED FROM PHASE 1 INCLUDING (A) THE NEED FOR REGION-SPECIFIC SENSOR CALIBRATION; AND (B) DIFFICULTY IN RECRUITING CITIZEN SCIENTISTS FOR EVERY SATELLITE PIXEL OF INTEREST. WE WILL MODIFY RECRUITMENT CRITERIA AND INTENSIFY OUTREACH TO RECRUIT CITIZEN SCIENTISTS. WE WILL EXTEND CITIZEN SCIENCE ACTIVITY AND SENSOR DEPLOYMENT TO A TOTAL OF THREE REGIONS TO BETTER CHARACTERIZE AOD-PM2.5 RELATIONSHIPS IN A VARIETY OF CONDITIONS. THE WIDESPREAD GLOBAL USE OF PURPLEAIR SENSORS (~1 000) AND THEIR EXISTING OPEN DATA TRANSFER FRAMEWORK (WIRELESS REAL-TIME TRANSFER) STRENGTHENS PROJECT SUSTAINABILITY. HENCE WE PROPOSE TO WORK CLOSELY WITH THE PURPLEAIR SENSOR MANUFACTURER (NEW COLLABORATOR) TO EXPAND ACCESS TO THESE DATA THEREBY INCREASING THE POOL OF CITIZEN SCIENTISTS TO CONTRIBUTE TO OUR PROJECT FRAMEWORK. ALL DATA WILL CONTINUALLY FEED TO A FLEXIBLE OPEN-SOURCE WEB PORTAL FOR BIAS-CORRECTION VISUALIZATION ARCHIVE AND ANALYSIS. UPON PROJECT COMPLETION WE PROPOSE TO INVOLVE LOCAL REGULATORY OR CITIZEN SCIENCE GROUPS TO CONTINUE THE PROGRAM USING THE ESTABLISHED FRAMEWORK FOR SUSTAINABILITY OF THE PROJECT. BY COMBINING DATA FROM SURFACE MEASUREMENTS (SENSORS FIXED MONITORS AERONET) SATELLITES (MODIS AOD AT 1- 3- AND 10-KM) AND REGIONAL AIR QUALITY MODEL (CMAQ) WE WILL EXAMINE THE AOD-PM2.5 RELATIONSHIP FOR EACH REGION AND ASSESS THE IMPACT OF SPATIAL RESOLUTION. THE IMPROVED SCIENTIFIC UNDERSTANDING FROM THIS PROJECT WILL IMPROVE THE VALUE OF AIR QUALITY DATASETS FROM NASAS CURRENT (MODIS VIIRS) AND FUTURE (TEMPO MAIA) MISSIONS AS WELL AS OTHER MISSIONS (NOAAS GOES-R; GOES-S; KOREAN GEMS; EUROPEAN SENTINAL-4).