4 research outputs found
Transport of Asian ozone pollution into surface air over the western United States in spring
Many prior studies clearly document episodic Asian pollution in the western U.S. free troposphere. Here, we examine the mechanisms involved in the transport of Asian pollution plumes into western U.S. surface air through an integrated analysis of in situ and satellite measurements in May–June 2010 with a new global high-resolution (∼50 × 50 km2) chemistry-climate model (GFDL AM3). We find that AM3 with full stratosphere-troposphere chemistry nudged to reanalysis winds successfully reproduces observed sharp ozone gradients above California, including the interleaving and mixing of Asian pollution and stratospheric air associated with complex interactions of midlatitude cyclone air streams. Asian pollution descends isentropically behind cold fronts; at ∼800 hPa a maximum enhancement to ozone occurs over the southwestern U.S., including the densely populated Los Angeles Basin. During strong episodes, Asian emissions can contribute 8–15 ppbv ozone in the model on days when observed daily maximum 8-h average ozone (MDA8 O3) exceeds 60 ppbv. We find that in the absence of Asian anthropogenic emissions, 20% of MDA8 O3 exceedances of 60 ppbv in the model would not have occurred in the southwestern USA. For a 75 ppbv threshold, that statistic increases to 53%. Our analysis indicates the potential for Asian emissions to contribute to high-O3 episodes over the high-elevation western USA, with implications for attaining more stringent ozone standards in this region. We further demonstrate a proof-of-concept approach using satellite CO column measurements as a qualitative early warning indicator to forecast Asian ozone pollution events in the western U.S. with lead times of 1–3 days
Global carbon monoxide products from combined AIRS, TES and MLS measurements on A-train satellites
This study tests a novel methodology to add value to satellite data sets. This
methodology, data fusion, is similar to data assimilation, except that the
background model-based field is replaced by a satellite data set, in this case
AIRS (Atmospheric Infrared Sounder) carbon monoxide (CO) measurements. The
observational information comes from CO measurements with lower spatial
coverage than AIRS, namely, from TES (Tropospheric Emission Spectrometer) and
MLS (Microwave Limb Sounder). We show that combining these data sets with data
fusion uses the higher spectral resolution of TES to extend AIRS CO
observational sensitivity to the lower troposphere, a region especially
important for air quality studies. We also show that combined CO measurements
from AIRS and MLS provide enhanced information in the UTLS (upper
troposphere/lower stratosphere) region compared to each product individually.
The combined AIRS–TES and AIRS–MLS CO products are validated against DACOM
(differential absorption mid-IR diode laser spectrometer) in situ CO
measurements from the INTEX-B (Intercontinental Chemical Transport
Experiment: MILAGRO and Pacific phases) field campaign and in situ data from
HIPPO (HIAPER Pole-to-Pole Observations) flights. The data fusion results
show improved sensitivities in the lower and upper troposphere (20–30%
and above 20%, respectively) as compared with AIRS-only version 5 CO
retrievals, and improved daily coverage compared with TES and MLS CO data