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Recently, oil and natural gas (O&NG) production activities in the Denver-Julesburg Basin have expanded rapidly. Associated nonmethane hydrocarbon (NMHC) emissions contribute to photochemical formation of ground-level ozone and include benzene as well as other hazardous air pollutants. Using positive matrix factorization (PMF) and chemical mass balance (CMB) methods, we estimate how much O&NG activities and other sources contribute to morning NMHC mixing ratios measured from 2013 to mid-2016 at a site in Platteville, CO, in the Denver-Julesburg Basin, and at a contrasting site in downtown Denver. A novel adjoint sensitivity analysis method is then used to estimate corresponding contributions to ozone and ozone-linked mortality in the Denver region. Average 6-9 am NMHC mixing ratios in Platteville were seven times higher than those in Denver in 2013 but four times higher in 2016. CMB estimates that O&NG activities contributed to the Platteville (Denver) site an average of 96% (56%) of NMHC on a carbon basis while PMF indicated 92% (33%). Average vehicle-related contributions of NMHC are estimated as 41% by CMB and 53% by PMF in Denver. Estimates of the fractional contribution to potential ozone and ozone-linked mortality from O&NG activities are smaller while those from vehicles are larger than the NMHC contributions. CMB (PMF) indicate that greater than 78% (40%) of annual average benzene in Denver is attributable to vehicle emissions while greater than 75% (67%) of benzene in Platteville is attributable to O&NG activities. AirWaterGas Sustainability Research Network - National Science Foundation [CBET-1240584] This research was supported in part by the AirWaterGas Sustainability Research Network funded by the National Science Foundation under Grant No. CBET-1240584. Any opinions, findings, and conclusions or recommendations expressed in this paper are those of the author and do not necessarily reflect the views of the National Science Foundation. The authors have declared that no competing interests exist. The CDPHE North Front Range Ozone Precursor Monitoring data are available at https://www.colorado.gov/airquality/tech_doc_repository.aspx.The CMAQ adjoint model and inputs are available upon request from the corresponding author.

The paper presents a version of the 4DVar method, capable of optimizing diurnal time profiles of emissions. It is a generalization of existing inverse methods that optimize emission daily totals. The core of the method is formed by the CMAQ adjoint model with SAPRC99 mechanism. Measurements from both ground–level stations (NO2 and O3), and satellites (retrieved columns of NO2 from GOME2 and OMI and the lowest layer of O3 retrieved from IASI) have been used as a data source for the inverse modeling procedure. The method can be used for detection of bias or errors in the emission model. It also can assist in development of data–driven emission model with location–specific time profiles of emissions. Different aspects of the method are illustrated on simulation experiments. Forecasting performance of the optimized model is evaluated for O3 and NO2 concentrations.