Direct identification of total and missing OH reactivities from light-duty gasoline vehicle exhaust in China based on LP-LIF measurement

Considerable efforts have been devoted to characterising the chemical components of vehicle exhaust.However,these components may not accurately reflect the contribution of vehicle exhaust to atmospheric reactivity because of the presence of species not accounted for(“missing species”)given the limitations of analytical instruments.In this study,we improved the laser photolysis–laser-induced fluorescence(LP-LIF)technique and applied it to directly measure the total OH reactivity(TOR)in exhaust gas from light-duty gasoline vehicles in China.The TOR for China Ⅰ to Ⅵ-a vehicles was 15.6,16.3,8.4,2.6,1.5,and 1.6×10^(4) sec^(-1),respectively,reflecting a notable drop as emission standards were upgraded.The TOR was comparable between cold and warm starts.The missing OH reactivity(MOR)values for China Ⅰ to Ⅳ vehicles were close to zero with a cold start but were much higher with a warm start.The variations in oxygenated volatile organic compounds(OVOCs)under different emission standards and for the two start conditions were similar to those of the MOR,indicating that OVOCs and the missing species may have similar production processes.Online measurement revealed that the duration of the stable driving stage was the primary factor leading to the production of OVOCs and missing species.Our findings underscore the importance of direct measurement of TOR from vehicle exhaust and highlight the necessity of adding OVOCs and other organic reactive gases in future upgrades of emission standards,such that the vehicular contribution to atmospheric reactivity can be more effectively controlled.

VOC emission caps constrained by air quality targets based on response surface model:A case study in the Pearl River Delta Region,China

Because of the recent growth in ground-level ozone and increased emission of volatile organic compounds(VOCs),VOC emission control has become a major concern in China.In response,emission caps to control VOC have been stipulated in recent policies,but few of them were constrained by the co-control target of PM_(2.5)and ozone,and discussed the factor that influence the emission cap formulation.Herein,we proposed a framework for quantification of VOC emission caps constrained by targets for PM_(2.5)and ozone via a new response surface modeling(RSM)technique,achieving 50%computational cost savings of the quantification.In the Pearl River Delta(PRD)region,the VOC emission caps constrained by air quality targets varied greatly with the NOxemission reduction level.If control measures in the surrounding areas of the PRD region were not considered,there could be two feasible strategies for VOC emission caps to meet air quality targets(160μg/m^(3)for the maximum 8-hr-average 90th-percentile(MDA8-90%)ozone and 25μg/m^(3)for the annual average of PM_(2.5)):a moderate VOC emission cap with<20%NOxemission reductions or a notable VOC emission cap with>60%NOxemission reductions.If the ozone concentration target were reduced to 155μg/m^(3),deep NOxemission reductions is the only feasible ozone control measure in PRD.Optimization of seasonal VOC emission caps based on the Monte Carlo simulation could allow us to gain higher ozone benefits or greater VOC emission reductions.If VOC emissions were further reduced in autumn,MDA8-90%ozone could be lowered by 0.3-1.5μg/m^(3),equaling the ozone benefits of 10%VOC emission reduction measures.The method for VOC emission cap quantification and optimization proposed in this study could provide scientific guidance for coordinated control of regional PM_(2.5)and O_(3)pollution in China.

黑碳气溶胶的稳定和放射性碳同位素研究进展

黑碳(black carbon, BC)气溶胶源自化石燃料和生物质的不完全燃烧,是重要的大气和气候污染物.稳定碳同位素(13C)和放射性碳同位素(14C)是目前进行大气BC来源定量解析最为准确和客观的手段之一.本文重点概述了13C和14C溯源的基本原理和我国大气环境BC源解析的最新进展.从目前13C和14C的分析结果看,我国大气环境BC的最大排放源是化石燃料的不完全燃烧,但生物质燃烧的贡献也可以达到20%~50%,值得进一步重视.化石源对BC的贡献表现出"夏高冬低"季节特征,突显了冬季生物质燃烧对大气环境BC的重要影响.利用14C对左旋葡聚糖的源示踪能力进行了评估,发现左旋葡聚糖在夏季可以发生严重的大气降解,不宜用于定量示踪大气环境BC的排放源.最后,本文总结了目前我国BC排放清单存在的不确定性情况,指出碳同位素技术可以在BC清单准确性提高上发挥重要作用,从而进一步加深目前科学界对BC环境和气候效应的认识.

Characterization of VOC emissions from construction machinery and river ships in the Pearl River Delta of China

Speciated characterization of Volatile Organic Compounds (VOCs),including oxygenated VOCs (OVOCs),from construction machinery and river ships in China is currently lacking.In this regard,we conducted field measurement on speciated VOC (including OVOC) emissions from six construction machinery and five river ships in the Pearl River Delta (PRD) region to identify VOC emission characteristics.We noticed that OVOC emissions from construction machinery and ships accounted for more than 50%of the total VOC emissions,followed by alkenes,aromatics and alkanes.Formaldehyde and acetaldehyde were the most emission species,accounting for 61.8%-83.2%of OVOCs.For construction machinery,the fuel-based emission factors of roller,grader and pile driver were 3.12,3.12 and 7.36 g/kg,respectively.With the rigorous restraint by the national emission standards,VOC emissions of construction machinery had decreased considerably,especially during stageⅢ.Ozone formation potential was also significantly reduced due to the significant decrease in emissions of OVOCs and alkenes with higher reactivity.For river ships,the fuel-based emission factors of cargo ships and speedboat were 1.46 and 0.44 g/kg,respectively.VOC emissions from construction machinery and river ships in Guangdong Province in 2017 were 8851.0 and 4361.0 ton,respectively.This study filled the knowledge gaps of reactive gas emissions from different kinds of non-road mobile sources over the PRD,and more importantly,highlighted the necessity in adding OVOC measurement to give a complete and accurate depiction of reactive gas emissions from non-road mobile sources.

Emission source-based ozone isopleth and isosurface diagrams and their significance in ozone pollution control strategies

In the past decade,ozone(O_(3))pollution has been continuously worsening in most developing countries.The accurate identification of the nonlinear relationship between O_(3) and its precursors is a prerequisite for formulating effective O_(3) control measures.At present,precursor-based O_(3) isopleth diagrams are widely used to infer O_(3) control strategy at a particular location.However,there is frequently a large gap between the O_(3)-precursor nonlinearity delineated by the O_(3) isopleths and the emission source control measures to reduce O_(3) levels.Consequently,we developed an emission source-based O_(3) isopleth diagram that directly illustrates the O_(3) level changes in response to synergistic control on two types of emission sources using a validated numerical modeling system and the latest regional emission inventory.Isopleths can be further upgraded to isosurfaces when co-control on three types of emission sources is investigated.Using Guangzhou and Foshan as examples,we demonstrate that similar precursor-based O_(3) isopleths can be associated with significantly different emission source co-control strategies.In Guangzhou,controlling solvent use emissions was the most effective approach to reduce peak O_(3) levels.In Foshan,co-control of on-road mobile,solvent use,and fixed combustion sources with a ratio of 3:1:2 or 3:1:3 was best to effectively reduce the peak O_(3) levels below 145 ppbv.This study underscores the importance of using emission source-based O_(3) isopleths and isosurface diagrams to guide a precursor emission control strategy that can effectively reduce the peak O_(3) levels in a particular area.

Numerical model to quantify biogenic volatile organic compound emissions:The Pearl River Delta region as a case study

This article compiles the actual knowledge of the biogenic volatile organic compound(BVOC) emissions estimated using model methods in the Pearl River Delta(PRD) region, one of the most developed regions in China. The developed history of BVOC emission models is presented briefly and three typical emission models are introduced and compared. The results from local studies related to BVOC emissions have been summarized. Based on this analysis, it is recommended that local researchers conduct BVOC emission studies systematically, from the assessment of model inputs, to compiling regional emission inventories to quantifying the uncertainties and evaluating the model results. Beyond that,more basic researches should be conducted in the future to close the gaps in knowledge on BVOC emission mechanisms, to develop the emission models and to refine the inventory results. This paper can provide a perspective on these aspects in the broad field of research associated with BVOC emissions in the PRD region.

A meteorologically adjusted ensemble Kalman filter approach for inversing daily emissions:A case study in the Pearl River Delta,China

The conventional Ensemble Kalman filter(EnKF),which is now widely used to calibrate emission inventories and to improve air quality simulations,is susceptible to simulation errors of meteorological inputs,making accurate updates of high temporal-resolution emission inventories challenging.In this study,we developed a novel meteorologically adjusted inversion method(MAEInv)based on the EnKF to improve daily emission estimations.The new method combines sensitivity analysis and bias correction to alleviate the inversion biases caused by errors of meteorological inputs.For demonstration,we used the MAEInv to inverse daily carbon monoxide(CO)emissions in the Pearl River Delta(PRD)region,China.In the case study,60%of the total CO simulation biases were associated with sensitive meteorological inputs,which would lead to the overestimation of daily variations of posterior emissions.Using the new inversion method,daily variations of emissions shrank dramatically,with the percentage change decreased by 30%.Also,the total amount of posterior CO emissions estimated by the MAEInv decreased by 14%,indicating that posterior CO emissions might be overestimated using the conventional EnKF.Model evaluations using independent observations revealed that daily CO emissions estimated by MAEInv better reproduce the magnitude and temporal patterns of ambient CO concentration,with a higher correlation coefficient(R,+37.0%)and lower normalized mean bias(NMB,-17.9%).Since errors of meteorological inputs are major sources of simulation biases for both low-reactive and reactive pollutants,the MAEInv is also applicable to improve the daily emission inversions of reactive pollutants.