Insights to the formation of secondary inorganic PM_(2.5):Current knowledge and future needs

As a criteria pollutant,fine particulate matter(fine PM,i.e.PM_(2.5))adversely affects public health and environment,contributes to visibility degradation and regional haze.Atmospheric fine PM includes primary and secondary PM_(2.5).While the primary PM_(2.5) is from direct emissions,the secondary PM_(2.5) is formed in the atmosphere through photochemical reaction,condensation and other atmospheric processes.Although it is well known that ammonia(NH3)may react with acidic gas species to form secondary inorganic PM_(2.5)(iPM_(2.5))as ammonium salts,limited research has been done to quantify the impacts of NH_(3) emissions of animal feeding operations(AFOs)on the dynamics of such chemical reactions and gas-particle phases partitioning.This paper is to provide comprehensive review of existing research on AFO PM chemical speciation and on the formation of secondary iPM_(2.5) as impacted by AFO air emissions.Research gaps and future studies in characterizing AFO PM and assessing impacts of AFO air emissions on atmospheric PM are discussed.