Increasingly severe air pollution over metropolitan regions in China has raised attention in light of its local and regional impacts on health and climate. Computer models can simulate complex interactions between photochemistry and meteorology to inform policy decisions in reducing ground-level pollution. However, models rely on an accurate portrayal of emissions that often possess large uncertainties over regions with evolving pollution characteristics. This work is comprised of a quantitative analysis of air pollutants in the North China Plain that strives to improve such uncertainties by identification of important sources and meteorological conditions for pollution through the combination of observations and models. Measurements used in this dissertation focus on in situ observations from the Spring 2016 Air chemistry Research in Asia (ARIAs) campaign, which sampled atmospheric composition across the heavily populated and industrialized Hebei Province in the North China Plain. High amounts of ozone (O3) precursors were found throughout and even above the planetary boundary layer, continuing to generate O3 at high rates to be potentially transported downwind. Evidence for the importance of anthropogenic VOCs on O3 production is presented. Concentrations of NOx and VOCs even in the rural areas of this highly industrialized province promote widespread O3 production and in order to improve air quality over Hebei, both NOx and VOCs should be regulated. The ARIAs airborne measurements also provide a critical opportunity to characterize chlorofluorocarbons (CFCs) over a suspected CFC-11 source region in China, finding mixing ratios were well above 2016 global background levels. Based on correlations of CFCs with compounds used in their manufacture, I identify likely source regions of new CFCs production and release, in violation of the Montreal Protocol. Finally, I examine the influence of meteorology on surface and aloft measurements during ARIAs. A multiday persistent high pressure episode is presented as a case study to examine the influence of regional transport on air quality measured during ARIAs. This dissertation provides valuable information for understanding one of the most polluted regions in China. Coordinated field and modeling efforts can together provide scientific guidance to inform pollution control measures to meet air quality targets in China.