AbstractResidential biomass burning (BB) plays an important role in the generation of household energy in rural China and can contribute to the degradation of regional air quality. Here, unexpectedly strong residential BB emissions were identified during the EXPeriment on the eLucidation of the atmospheric Oxidation capacity and aerosol foRmation, and their Effects in Yangtze River Delta (YRD) campaign in the rural area of the Eastern China based on the early summertime measurements of non‐methane organic gases (NMOGs) by a Proton Transfer Reaction‐Quadruple Time‐of‐Flight Mass Spectrometer. These widespread and long‐lasting residential BB emissions feature high levels of acetonitrile, oxygenated‐aromatics, and naphthalene, and are independent of the characteristic emissions from the open field BB but relate to miscellaneous fuels burning such as combustible wastes. The positive matrix factorization approach was applied to quantitatively appoint sources and understand the role of residential BB on OH reactivity (L_OH) and secondary organic aerosols formation potential (SOAP) in the rural atmosphere of China. We find that residential BB accounts for 24.0% ± 6.4% of all NMOG mixing ratios, compared to 40.1% ± 7.7% of urban emissions. The contribution of these two sources to the total calculated L_OH (23.2% ± 6.2% from BB and 26.4% ± 5.1% from urban) and SOAP (22.0% ± 7.5% from BB and 23.2% ± 6.7% from urban) are comparable during normal days. In addition, biogenic emissions and sporadic field BB are also important sources of NMOGs in the YRD region during the harvest season. This study highlights the critical importance of residential BB emissions in the Eastern China, which were unaccounted for by the past air pollution regulations.