The purpose of this report is to provide specific guidance for collection of ozone and precursor data, where, needed to define upwind transport into cities. Certain requirements or recommendations for upwind monitoring have been made in connection with the Level 111 modeling analysis recommend as the minimum modeling requirement in the development of 1982 ozone SIPs. In addition, some states and localities may wish to perform more sophisticated modeling. This supplementary, specific guidance for upwind monitoring is needed because several changes have been made in the monitoring system and strategies. This report attempts to describe the above circumstances more completely and provides guidance in effectively carrying out an upwind monitoring program. The guidance is based primarily on the results of a special field study conducted in the Philadelphia area during the summer of 1978 for the purpose of evaluating approaches for measuring ozone and its precursors upwind of an urban area. Five approaches from among those consider possible were field tested, and the findings form a principle basis for the recommendations made in this report. The following sections describe the 1978 field study and its principle findings. The study was performed under contract to EPA by AeroVironment, Inc.