SENSITIVE AND ACCURATE MEASUREMENTS OF GAS PHASE AMMONIA WILL BE MADE ON THE NASA DC-8 AIRCRAFT FOR FIRECHEM AND BE INCORPORATED INTO THE NOAA GFDL AM3 MODEL TO BETTER UNDERSTAND THE IMPACT OF BIOMASS BURNING ON THE AMMONIA BUDGET AND AMMONIUM NITRATE FORMATION OVER NORTH AMERICA. AMMONIA IS AN IMPORTANT PRECURSOR SPECIES FOR FINE PARTICULATE MATTER AND AMMONIUM DOMINATES PARTICLE COMPOSITION ON A MOLAR BASIS WHICH IS THE RELEVANT METRIC FOR UNDERSTANDING PARTICLE CHEMISTRY. AMMONIA EMISSIONS ARE POORLY CONSTRAINED AND BIOMASS BURNING IS THOUGHT TO BE A LARGE CONTRIBUTION TO THE FREE TROPOSPHERIC NH3 BUDGET THROUGH CONVECTIVE LOFTING OF RISING PLUMES. AN EXISTING OPEN-PATH QUANTUM CASCADE LASER-BASED AMMONIA SENSOR WILL BE INTEGRATED ONTO THE DC-8 AIRCRAFT TO MAKE THESE MEASUREMENTS. THE OPEN-PATH CONFIGURATION ENSURES FAST RESPONSE TIME AND AVOIDS THE PROBLEMATIC ADSORPTION AND DESORPTION EFFECTS COMMON TO CLOSED PATH SYSTEMS BIASES WHICH ARE DIFFICULT TO QUANTIFY AND ULTIMATELY DETERMINE THE MEASUREMENT ACCURACY. THE SENSOR WILL HAVE HIGH PRECISION (30 PPTV AT 1 HZ) TO DISCERN NARROW FIRE PLUME SIGNATURES. ACCURACY WILL BE (15% + 0.2 PPBV) FOR ONE SECOND INTEGRATION TIMES. THE AMMONIA SENSOR HAS BEEN SUCCESSFULLY FIELD-DEPLOYED IN THE PAST IN A RANGE OF HARSH ENVIRONMENTS ON THE GROUND AND THE DATA HAS ALREADY BEEN USED FOR THE FIRST PIXEL-SCALE VALIDATION OF THE NASA TES SATELLITE. THE OPTOMECHANICAL CONFIGURATION FOR THE DC-8 INTEGRATION WILL BE IDENTICAL TO THE EXISTING SENSOR. SPECIFIC OBJECTIVES OF THIS PROPOSAL INCLUDE THE FOLLOWING: 1. WHAT IS THE VARIABILITY OF AMMONIA EMISSION RATIOS (FACTORS) FROM FRESH NORTH AMERICAN FIRES? 2. WHAT IS THE EFFICIENCY OF NH3 CONVERSION TO NHX AS PLUMES AGE DOWNWIND OF THE FIRE? 3. HOW WELL DO SATELLITES MEASURE NH3 FROM BIOMASS BURNING? 4. HOW DOES BIOMASS BURNING CONTRIBUTE TO TROPOSPHERIC NH3 AND NH4NO3 OVER NORTH AMERICA THESE OBJECTIVES WILL BE ACHIEVED BY INTEGRATING THE AMMONIA SENSOR ONTO THE DC-8 PERFORMING CALIBRATIONS BEFORE DURING AND AFTER THE FIELD PHASES AND ARCHIVING THE DATA PER SCIENCE TEAM PROTOCOLS. THE AIRCRAFT DATA WILL BE SYNTHESIZED WITH OTHER AIRCRAFT-BASED AND SATELLITE MEASUREMENTS. THE IN-SITU DATA WILL HELP WITH SATELLITE VALIDATION OF IASI CRIS AND AIRS BOTH IN TERMS OF UNDERSTANDING THE REPRESENTATIVENESS OF SATELLITE MEASUREMENTS OF EMISSION RATIOS COMPARED TO AIRCRAFT-BASED MEASUREMENTS AND IN TERMS OF QUANTIFYING THE FREE TROPOSPHERIC AMMONIA BURDEN (A SIGNIFICANT SOURCE OF UNCERTAINTY WHEN VALIDATING SATELLITE NH3 PRODUCTS). THE IN-SITU AND SATELLITE MEASUREMENTS WILL BE INCORPORATED INTO THE NOAA GFDL AM3 MODEL TO BETTER UNDERSTAND THE SOURCES OF PARTICULATE MATTER IN NORTH AMERICA.