The primary sources for inorganic aerosols from biomass burning are rather negligible, but they are predominantly formed chemically following emission of their precursors (e.g., SO2, NH3, HOx, and NOx). The biomass burning contributions to some of the precursors can be considerable. Accordingly, we quantify the impact of the emissions on major inorganic aerosols in April–October 2012–2014 using a regional model simulation verified by extensive surface observations throughout the U.S. Simulated CO enhancements on an hourly basis are used to classify the U.S. into weak‐moderate (5 < COBiomass‐COBase < 20 ppbv) and strongly impacted periods (COBiomass‐COBase > 20 ppbv). This separation not only facilitates the identification of the spatial frequency of the impact but also helps to filter out nonimpacted periods, enabling us to focus on long‐term contributions. Despite the nonlinear responses of several trace gases to emissions, we observe increases (weak‐moderate and strong) in daily surface SO42− (1.16 ± 0.32 and 6.57 ± 4.65 nmol/m3), NO3− (0.36 ± 0.63, 4.70 ± 7.05 nmol/m3), and NH4+ (2.70 ± 0.92 and 17.82 ± 15.17 nmol/m3) on a national scale. These primarily resulted from (i) increases in daily surface SO2 (0.02 ± 0.01 and 0.10 ± 0.07 ppbv), afternoon OH (1.28 ± 4.24 and 12.82 ± 23.76 ppqv), and H2O2 (0.06 ± 0.02 and 0.10 ± 0.08 ppbv), which may have accelerated the conversion of S(IV) to S(VI), and (ii) increases in daily surface NH3 (1.08 ± 0.73 and 8.61 ± 7.73 nmol/m3) and HNO3 (1.44 ± 0.48 and 7.15 ± 4.25 nmol/m3), which could have produced more particle‐phase NH4NO3. In the West, where atmospheric moisture is limited, enhanced SO42− leaves less available water for NH4NO3 to become ions. Our results suggest that the major inorganic aerosol enhancement (mass) can reach to 23% of that of the carbonaceous aerosols.
A number of satellite‐based instruments have become an essential part of monitoring emissions. Despite sound theoretical inversion techniques, the insufficient samples and the footprint size of current observations have introduced an obstacle to narrow the inversion window for regional models. These key limitations can be partially resolved by a set of modest high‐quality measurements from airborne remote sensing. This study illustrates the feasibility of nitrogen dioxide (NO2) columns from the Geostationary Coastal and Air Pollution Events Airborne Simulator (GCAS) to constrain anthropogenic NOx emissions in the Houston‐Galveston‐Brazoria area. We convert slant column densities to vertical columns using a radiative transfer model with (i) NO2 profiles from a high‐resolution regional model (1 × 1 km2) constrained by P‐3B aircraft measurements, (ii) the consideration of aerosol optical thickness impacts on radiance at NO2 absorption line, and (iii) high‐resolution surface albedo constrained by ground‐based spectrometers. We characterize errors in the GCAS NO2 columns by comparing them to Pandora measurements and find a striking correlation (r > 0.74) with an uncertainty of 3.5 × 1015 molecules cm−2. On 9 of 10 total days, the constrained anthropogenic emissions by a Kalman filter yield an overall 2–50% reduction in polluted areas, partly counterbalancing the well‐documented positive bias of the model. The inversion, however, boosts emissions by 94% in the same areas on a day when an unprecedented local emissions event potentially occurred, significantly mitigating the bias of the model. The capability of GCAS at detecting such an event ensures the significance of forthcoming geostationary satellites for timely estimates of top‐down emissions.
Abstract. Accurate meteorological fields are imperative for correct chemical transport modeling. Observation nudging, along with objective analysis, is generally considered a lowcost and effective technique to improve meteorological simulations. However, the meteorological impact of observation nudging on chemistry has not been well characterized. This study involved two simulations to analyze the impact of observation nudging on simulated meteorology and ozone concentrations during the 2013 Deriving Information on Surface conditions from Column and Vertically Resolved Observations Relevant to Air Quality (DISCOVER-AQ) Texas campaign period, using the Weather Research and Forecasting (WRF) and Community Multiscale Air Quality (CMAQ) models. The results showed improved correlations between observed and simulated parameters. For example, the index of agreement (IOA) improved by about 9 % for surface temperature and 6-11 % for surface zonal (U-WIND) and meridional (V-WIND) winds when observation nudging was employed. Analysis of a cold front event indicated that nudging improved the timing of wind transition during the front passage. Observation nudging also reduced the model biases for the planetary boundary layer height predictions. Additionally, the IOA for CMAQ simulated surface ozone improved by 6 % during the simulation period. The high-ozone episode on 25 September was a post-front ozone event in Houston. The small-scale morning wind shifts near the Houston Ship Channel combined with higher aloft ozone early morning likely caused the day's ozone exceedance. While observation nudging did not recreate the wind shifts on that day and failed to reproduce the observed high ozone, analyses of surface and aircraft data found that observation nudging helped the model yield improved ozone predictions. In a 2 h period during the event, substantially better winds in the sensitivity case noticeably improved the ozone. The average IOA for ozone in the period increased from just over 0.4 to near 0.7. Further work on improving the capability of nudging to reproduce local meteorological events such as stagnations and wind reversals could enhance a chemical transport model's skill for predicting high-ozone events.
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