Smoke and NO x emission characteristics of in-use construction machinery base on substantial field measurement: A case study in Beijing, China

To understand the smoke level and NO emission characteristics of in-use construction machinery in Beijing, we selected 905 construction machines in Beijing from August 2022 to April 2023 to monitor the emission level of smoke and NO . The exhaust smoke level and excessive emission situation of different machinery types were identified, and their NO emission levels were monitored according to the free acceleration method. We investigated the correlation of NO and smoke emission, and proposed suggestions for controlling pollution discharge from construction machinery in the future. The results show that the exhaust smoke level was 0-2.62 m , followed a log-normal distribution (μ = -1.73, δ = 1.09, R = 0.99), with a 5.64% exceedance rate. Differences were observed among machinery types, with low-power engine forklifts showing higher smoke levels. The NO emission range was 71-1516 ppm, followed a normal distribution (μ = 565.54, δ = 309.51, R = 0.83). Differences among machinery types were relatively small. Engine rated net power had the most significant impact on NO emissions. Thus, NO emissions from construction machinery need further attention. Furthermore, we found a weak negative correlation (p < 0.05) between the emission level of smoke and NO , that is the synergic emission reduction effect is poor, emphasizing the need for NO emission limits. In the future, the oversight in Beijing should prioritize phasing out China Ⅰ and China Ⅱ machinery, and monitor emissions from high-power engine China Ⅲ machinery.