ABSTRACT

On-road remote sensing measurements of light and medium-duty gasoline vehicles collected within California’s South Coast Air Basin since 1999 generally fall within the range of observed summer ambient molar NO_x/CO measurements collected during morning rush hours. Compared with ambient and on-road emissions, the California Air Resources Board EMFAC model underpredicts 2018 gasoline vehicle NO_x emission factors by more than a factor of 2.6. Contributing to these differences is that vehicles older than model year 2006 have NO_x emission deterioration rates that are up to four times higher on-road than predicted by the EMFAC model. A fuel-based inventory using the 2018 on-road gasoline emission factors for CO and NO_x results in total CO emissions similar to the basin inventory but NO_x emissions that are 74% higher than the inventory. The higher NO_x emission estimates from on-road gasoline vehicle measurements make their contribution to the inventory slightly larger than heavy-duty diesel vehicles. We have found LEV I (1994–2003) gasoline vehicles are a major source of these on-road emissions and that significant NO_x reductions in the South Coast Air Basin are being overlooked by not targeting the high emitters for removal.

Implications: A comparison of ambient and on-road vehicle molar NO_x/CO ratios collected in California’s South Coast Air Basin with those predicted by California’s EMFAC2017 vehicle emissions model shows that the model significantly underpredicts NO_x emission factors for gasoline vehicles. This results in a 74% underestimate of the contribution of gasoline vehicles to the basin’s NO_x inventory, with the contribution from gasoline vehicles comparable to that from heavy-duty diesel trucks. This likely means that current projections for future NO_x emission reductions from mobile sources in the basin will not be realized unless additional NO_x reductions are obtained from older gasoline vehicles.

摘要

自 1999 年以来在加利福尼亚州南海岸空气盆地内收集的轻型和中型汽油车辆的道路遥感测量值通常属于在早高峰时段收集的夏季环境摩尔 NO _x /CO 测量值的范围内。随着环境和道路上的排放相比，加州空气资源委员会EMFAC模型underpredicts 2018汽油车NO _X超过2.6倍的排放因子。导致这些差异比模型大一岁，是2006年的车辆有没有_X排放恶化率较高是高达四倍的公路不是由EMFAC模型预测。使用 2018 年道路汽油排放因子的 CO 和 NO _x的基于燃料的清单导致 CO 总排放量与流域清单相似，但 NO _x排放量比清单高 74%。来自公路汽油车测量的较高 NO _x排放估计使其对库存的贡献略大于重型柴油车。我们发现 LEV I (1994-2003) 汽油车是这些道路排放的主要来源，南海岸空气盆地的NO _x显着减少被忽视，因为没有针对高排放者进行去除。

影响：在加利福尼亚州南海岸空气盆地收集的环境和道路车辆 NO _x /CO摩尔比与加利福尼亚州 EMFAC2017 车辆排放模型预测的比较表明，该模型显着低估了汽油车辆的NO _x排放因子。这导致了汽油车的贡献盆地的NO的74％低估_X库存，以汽油车的贡献相媲美，从重型柴油卡车。这可能意味着，对于未来的NO目前的预测_X从在盆移动源排放减少量将无法实现，除非另外NO _X的减少被从旧汽油车获得。