NOx and NO2 were collected using Ogawa passive samplers with triethanolamine (TEA) as an absorbent. Each sampler collected NOx and NO2 over a 24-h period. Absorbed NOx and NO2 were examined colori- metrically (Axiom Spectrophotometer, Germany), per the manufacturer’s protocol (Ogawa & Company, USA, Inc. 2006). Standard solutions were prepared daily and samples were analyzed within 24 h of collection.